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1
Li, Yao. "Shear behaviour of sand in bi-directional direct simple shear tests." Thesis, University of Nottingham, 2016. http://eprints.nottingham.ac.uk/37279/.
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In geotechnical engineering, soil is subject to shear stress, as well as normal stress. In many cases, soil is sheared along multiple directions, such as an embankment under earthquake loading and foundation soil of a structure under a complex loading. In recent years, significant research has been devoted to understanding the static and cyclic shear behaviour of sand under complex stress conditions. To investigate the shear behaviours of soils, a few testing devices have been specifically developed. The most commonly used apparatuses are direct shear, direct simple shear, and hollow cylinder apparatuses. While each has its own merits, they share one common limitation. That is the soil specimens are sheared along only one direction in these devices, making it impossible to study the soil responses under multiple shear stresses encountered in many geotechnical engineering problems. It is widely acknowledged that testing stress path has a significant effect on shear stress, so specimens must be examined under a stress path similar to in-situ. In many cases, a simple shear apparatus closely duplicates the stress conditions in soil elements, and a bi-directional direct simple shear apparatus can create complex stress conditions. To investigate the shear behaviour of soils subject to complex loading conditions, several studies of multidirectional simple shear testing were performed on the first commercially available Variable Direction Dynamic Cyclic Simple Shear (VDDCSS) system. In the VDDCSS, the secondary shear actuator acting at 90 degrees to the primary shear actuator enables it to add shear stress in any horizontal direction. Various previously unexplored complex stress paths were tested in this study using the VDDCSS. Sand samples of Leighton Buzzard sand (Fraction B) were first subjected to consolidation shear stresses under drained conditions along different directions (from 0° to 180° to the X direction of the apparatus), followed by monotonic or cyclic secondary shear stresses along 0° until failure occurs. The magnitude and direction of the consolidation shear stress on the static and cyclic secondary shear behaviours of sand were systematically studied. In undrained static tests, soil strength was the lowest when the angles between the two shears stresses were near 90°, and the strength was the highest at 0°. In addition, a smaller angle produced a more brittle response, and a greater angle led to a more ductile response. The effect of stress path (the direction of consolidation shear stresses) was found to be more significant in tests with a greater magnitude of consolidation shear stresses, and the relationship between the angles (between the first shear stresses and secondary shear stresses) and shear behaviours was much more complex when the magnitude of consolidation shear stresses was increased. In drained static tests, the evidence of non-coaxiality was obtained. The non-coaxiality was the greatest at the initial stage of shearing, and it decreased to zero at higher shear strains. The degree of non-coaxiality was affected by the relative density of the specimen, vertical stress, level and direction of consolidation shear stress. In addition, the non-coaxiality was significantly affected by the consolidation shear stress, and the effect increased at a greater magnitude of consolidation shear stresses. The non-coaxiality increased as the angle was increased. In stress-controlled undrained dynamic tests, there was no significant difference in pore water generation rate among samples with consolidation shear stresses in different directions. However, samples with different directions of consolidation shear stresses failed at different numbers of cycles and in different directions. Liquefaction resistance was decreased by the increased magnitude of consolidation shear stress. In most of the tests with consolidation shear stress, the levels of liquefaction resistances were lower than that without consolidation shear stress. In strain-controlled undrained dynamic tests, liquefaction resistance (shear strength) was decreased from 0° to 90°, and increased from 90° to 180°. Liquefaction resistance in tests with consolidation shear stresses were lower than those without consolidation shear stress.
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Hassan, Zehtab Kaveh. "An Assessment Of The Dynamic Properties Of Adapazari Soils By Cyclic Direct Simple Shear Tests." Master's thesis, METU, 2010. http://etd.lib.metu.edu.tr/upload/12612228/index.pdf.
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Among the hard-hit cities during 17 August 1999 Kocaeli Earthquake (Mw 7.4), Adapazari is known for the prominent role of site conditions in damage distribution. Since the strong ground motion during the event was recorded only on a rock site, it is necessary to estimate the response of alluvium basin before any study on the relationship between the damage and the parameters of ground motion. Therefore, a series of site and laboratory tests were done on Adapazari soils in order to decrease the uncertainty in estimation of their dynamic properties. In downtown Adapazari, a 118 m deep borehole was opened in the vicinity of heavily damaged buildings for sample recovery and in-situ testing. The stiffness of the soils in-situ is first investigated by standard penetration tests (SPT) and by velocity measurements with P-S suspension logging technique. Disturbed samples were recovered by core-barrel and split-barrel samplers. 18 Thin-Walled tubes were successively used for recovering undisturbed samples. A series of monotonic and cyclic direct simple shear tests were done on specimens recovered from the Thin-Walled tubes. It is concluded that the secant shear modulus and damping ratio of soils exposed to severe shaking during the 1999 event are significantly smaller than those estimated by using the empirical relationships in literature. It is also observed that the reversed-S shaped hysteresis loops are typical for cyclic response of the samples.
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Babalola, Zainab. "Direct shear and direct simple shear tests: a comparative study of the strength parameters and their dependence on moisture and fines contents." Master's thesis, University of Cape Town, 2016. http://hdl.handle.net/11427/20922.
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Shear strength of soil is characterized by cohesion, angle of internal friction and dilatation. The first two parameters mentioned primarily define the soil's ability to resist shear stress underspecified load. These parameters can be determined by tests conducted either in the laboratory or the field for use in design of geotechnical structures. Some of the tests in the laboratory to determine the shear strength of soil, include triaxial, ring shear, torsional shear, direct shear and direct simple shear. Direct shear test is the most widely used geotechnical shear device due to its simplicity, however, the test suffers from stress inhomogeneity. Direct simple shear apparatus was developed because of the shortcomings in the direct shear test. In these two tests, different shearing conditions are applied to soil samples. For the direct shear test, shearing occurs at a predetermined center of the specimen which may not be the weakest plane of the soil while indirect simple shear, the entire specimen distorts without the formation of single shearing surface. The mode of shearing established in the direct simple shear device is similar to that which occurs around the shaft of a pile. In contrast to the extensive geotechnical application of direct shear test, limited information exists on direct simple shear test. This thesis endeavours to establish the relationship between the two tests by undertaking extensive testing to obtain a better understanding of direct simple shear test as used for testing local soils and to determine a correlation with the results from direct shear tests. A series of shear tests were undertaken on Klipheuwel sand, Kaolin clay and composite of the sand and clay using universal shear device. The soils were mixed with water in percentages of 5,10, 15, 20 and 25%, and the composite with clay percentages of 10, 25, 50 and 75%, to investigate the impact of water and clay on the shear parameters determined from the two tests. The results showed that direct shear test gives higher shear strength when compared to direct simple shear test under the same soil condition. The addition of water, and clay, generally reduced the internal friction angle of sand for both tests. Furthermore, increase in cohesion was observed with the addition of water to Kaolin clay for the direct simple shear test and the reverse was true in the direct shear test. The correlation factors developed in this study for the direct simple shear test could be used to refine the results from the direct shear test.
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Dabeet, Antone. "Discrete element modeling of direct simple shear response of granular soils and model validation using laboratory tests." Thesis, University of British Columbia, 2014. http://hdl.handle.net/2429/48510.
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The direct simple shear (DSS) device is one of the most commonly used laboratory testing tools to characterize the shear behavior of soils. In the Norwegian Geotechnical Institute (NGI) version of the DSS test, where a cylindrical soil specimen is confined by a wire-reinforced membrane, only normal and shear stresses on the horizontal planes are measured. The knowledge of these stresses alone does not provide adequate information to calculate friction angles for use in geotechnical design. Further, the absence of complementary shear stresses at the soil-membrane interface causes stress non-uniformities within DSS specimens, which makes the task of interpreting DSS testing results even more difficult. With the recent advances in computers, it is now possible to model soil in a realistic manner as a collection of particles using the discrete element method (DEM). With this background, a DEM model of a cylindrical DSS specimen was developed to provide insight on the state of stress and strain in DSS specimens. A laboratory DSS testing program was undertaken on glass beads as part of this study. The results of the glass beads tests were used for comparison with the DEM model results. Further, free-form sensors (paper-thin flexible pressure sensors mounted on the reinforced part of the DSS membrane) were used to measure lateral stresses acting on reconstituted Fraser River silt specimens. It was shown that: i) the adopted DEM modeling approach is effective in capturing the salient characteristics of the DSS behavior of the tested glass beads; ii) during the shearing phase, the distribution of shear strains across the specimen is more uniform at lower shear strain levels; iii) significant stress non-uniformities during shearing are limited to a narrow zone of about two particles diameter near the lateral boundaries, while stresses at central specimen locations are relatively more uniform (i.e. most representative of “ideal” simple shear conditions); and iv) at large shear strains, the horizontal plane becomes the plane of maximum obliquity, and the friction angle calculated using the stress state on the horizontal plane is a good approximation to the mobilized friction angle at such strain levels.Applied Science, Faculty of
Civil Engineering, Department of
Graduate
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Persson, Erik. "Empirical correlation between undrained shear strength and preconsolidation pressure in Swedish soft clays." Thesis, KTH, Jord- och bergmekanik, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-213848.
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The undrained shear strength and preconsolidation pressure are key parameters in describing the characteristics of soft clays. The two parameters both reflect the clay’s structure and state of stress, and hence empirical correlations for undrained shear strength normalized with respect to preconsolidation pressure are widely used to assess soil behavior. The empirical correlations given in the literature are typically dependent on liquid limit, or plasticity index, but some studies have questioned the dependency and proposed correlations constant for consistency limits. Data from geotechnical projects often display a considerable scatter and deviate from established empirical correlations. In this thesis, statistical analyses are performed and evaluated qualitatively on direct simple shear, constant rate of strain and fall cone test data from 146 sampling points with a total of 596 soil samples from Stockholm, Gothenburg and Uppsala. The aim is to investigate the correlation between shear strength and the preconsolidation pressure. The thesis evaluates the normalized shear strength’s dependency on liquid limit, how the data corresponds to Hansbo’s (1957) and Swedish Geotechnical Institute’s (2007) linear empirical correlations, and the correction factor applied to shear strength measured by the fall cone test. The results of the study show that the correction factor typically reduces the shear strength from fall cone tests too much with respect to shear strength from direct simple shear tests. The normalized shear strength’s dependency on liquid limit may be rejected for the fall cone test data. The results for direct simple shear test data however, indicates a correlation with liquid limit. The data scatter is considerable, especially for fall cone test data, and the relevance of describing the normalized shear strength from fall cone test with a linear empirical correlation to liquid limit may conclusively be questioned.Skjuvhållfasthet och förkonsolideringstryck är två viktiga jordparametrar för lösa leror. Båda parametrar reflekterar lerans struktur och spänningstillstånd, och empiriska korrelationer för odränerad skjuvhållfasthet, normaliserad mot förkonsolideringstrycket, används därför ofta för att bedöma en leras egenskaper. De empiriska korrelationerna är vanligen kopplade till flytgräns eller plasticitetsindex. Dessa korrelationer har däremot ifrågasatts av studier som i vissa fall istället föreslagit ett konstant förhållande mellan normaliserad odränerad skjuvhållfasthet och plasticitetsgränser. Mätvärden från geotekniska projekt i Sverige visar allmänt stor spridning avseende dessa parametrar och data avviker ofta från etablerade empiriska korrelationer. I examensarbetet har data från direkta skjuvförsök, ödometerförsök och fallkonförsök utvärderats statistiskt och kvalitativt. Totalt omfattar studien 596 jordprover från 146 provtagningspunkter från Stockholm, Göteborg och Uppsala. Syftet med studien är att undersöka korrelationen mellan odränerad skjuvhållfasthet och förkonsolideringstryck. Studien behandlar den normaliserade skjuvhållfashetens flytgränsberoende, Hansbos (1957) och Statens Geotekniska Instituts (2007) empiriska korrelationer, samt den korrektionsfaktor som ska tillämpas på skjuvhållfastheter från fallkonförsök. Resultatet visar att korrektionsfaktorn reducerar skjuvhållfastheten för mycket och att korrigerade skjuvhållfastheter är i sämre samstämmighet med skjuvhållfastheter från direkta skjuvförsök än okorrigerade. Data från fallkonförsök uppvisar inget tydligt flytgränsberoende, medan resultaten från direkta skjuvförsök indikerar ett beroende. Spridningen i data är dock påfallande, särskilt för fallkonförsöket. Relevansen i att tillämpa en linjär empirisk korrelation för odränerad normaliserad från fallkonförsök mot förkonsolideringstryck beroende av flytgräns bör ifrågasättas.
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Arrelucé, Montenegro Sebastian, and Larrauri Grecia Luciana Solís. "Incorporación de fibras de polipropileno como método de reforzamiento de suelos arcillosos en Palian - Huancayo." Bachelor's thesis, Universidad Peruana de Ciencias Aplicadas (UPC), 2021. http://hdl.handle.net/10757/656164.
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Esta tesis tiene como objetivo evaluar un método de reforzamiento propuesto en base a la incorporación de fibras de polipropileno con la finalidad de incrementar la resistencia y mejorar las características mecánicas del suelo arcilloso de Palian – Huancayo.
La arcilla es un suelo cohesivo constituido por partículas finas, estas características determinan la capacidad de deformación y compresión, además poseen baja resistencia al corte y a cargas. Debido a ello se busca reforzar y mejorar el comportamiento mecánico de la arcilla mediante métodos físicos y químicos.
Esta investigación propone la adición fibras de polipropileno como método de reforzamiento para lo cual se analizó el suelo remoldeado con diferentes porcentajes de fibras adicionadas 0.1, 0.2, 0.3, 0.4 y una longitud de fibra de 10 milímetros. Se realizaron ensayos de caracterización física para identificar el suelo natural remoldeado: granulometría por sedimentación, límites de consistencia y gravedad específica de los sólidos. Se sometió el suelo natural remoldeado y las mezclas con diferentes porcentajes de fibras a los siguientes ensayos de caracterización mecánica para determinar las variaciones en el comportamiento: ensayo de compactación estándar, ensayo de corte directo y ensayo de compresión simple.
Los valores obtenidos mediante los ensayos realizados demostraron la mejora de las características mecánicas del suelo siendo la mezcla de 0.4% de fibras de polipropileno la que brinda un mejor resultado en comparación con las mezclas de menor proporción.This thesis aims to evaluate a reinforcement method based on the incorporation of polypropylene fibers to increase the strength and improve the mechanical characteristics of Palian- Huancayo’s clay soil. Clay is a cohesive soil consisting of fine particles, these characteristics determine the capacity of deformation and compression, as well as low resistance to cutting and loads. Therefore, it seeks to strengthen and improve the mechanical behavior of clay through physical and chemical methods. This research proposes the addition of polypropylene fibers as reinforcement method for which the soil under study was analyzed with different percentages of fibers added 0.1, 0.2, 0.3, 0.4 and a fiber length of 10 millimeters. Physical characterization tests were carried out to identify the natural soil: granulometry by sedimentation, limits of consistency and specific gravity of the solids. The natural soil and the mixtures with different percentages of fibers were subjected to the following mechanical characterization tests to determine the variations in behavior: Standard compaction test, unconfined compression test, and shear direct test. The values obtained through the tests demonstrated the improvement of the mechanical characteristics of the soil being the mixture of 0.4% of polypropylene fibers the one that provides a better result compared to the mixtures of a lower proportion.
Tesis
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Laham, Noor. "Episodic DSS tests to measure changing strength for whole-life geotechnical design." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2020.
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Changes in seabed soil strength due to loading events during the life of a structure, affect the response of the structure to any future event. This change in soil strength due to loading events, in particular cyclic loads, was of great concern in the field of offshore geotechnics during the last decades. Allowing for these changes can have a beneficial outcome on the design. Studying the changes occurring in the soil can be mainly done using large scale centrifuge tests or Laboratory element testing, where the latter proved to be able to successfully illustrate soil strength changes during periods of cyclic loads and reconsolidation.
A new approach of life design known as “the whole life design” has been introduced lately to the industry “. Whole life design embraces the time-varying evolution of actions and resistances to create a continuous assessment of conditions of a structure.
This dissertation studies the possibility of one of the most famous element tests which is the “Direct simple shear testing” to capture the changing in strength under cyclic (i.e., episodic in this context) loads and the settlement of subsea layers for the whole life geotechnical design. The outcome of the DSS testing in addition to outcomes from other previous methods (eg T-bar penetrations and Triaxial testing) can form the basis for a new framework to be adopted in the future for demonstrating a whole life design for subsea structures.
In general, the project introduces the concept of whole-life geotechnical design through practical examples and shed lights on Direct simple shear testing ability to simulate specific cyclic loading scenarios. The topic closes with a discussion of next steps to enable whole-life geotechnical design to be more readily adopted in routine practice where appropriate.
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Zhang, Ling. "The behaviour of granular material in pure shear, direct shear and simple shear." Thesis, Aston University, 2003. http://publications.aston.ac.uk/14162/.
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In biaxial compression tests, the stress calculations based on boundary information underestimate the principal stresses leading to a significant overestimation of the shear strength. In direct shear tests, the shear strain becomes highly concentrated in the mid-plane of the sample during the test. Although the stress distribution within the specimen is heterogeneous, the evolution of the stress ratio inside the shear band is similar to that inferred from the boundary force calculations. It is also demonstrated that the dilatancy in the shear band significantly exceeds that implied from the boundary displacements. In simple shear tests, the stresses acting on the wall boundaries do not reflect the internal state of stress but merely provide information about the average mobilised wall friction. It is demonstrated that the results are sensitive to the initial stress state defined by K0 = sh/sv. For all cases, non-coaxiality of the principal stress and strain-rate directions is examined and the corresponding flow rule is identified. Periodic cell simulations have been used to examine biaxial compression for a wide range of initial packing densities. Both constant volume and constant mean stress tests have been simulated. The characteristic behaviour at both the macroscopic and microscopic scales is determined by whether or not the system percolates (enduring connectivity is established in all directions). The transition from non-percolating to percolating systems is characterised by transitional behaviour of internal variables and corresponds to an elastic percolation threshold, which correlates well with the establishment of a mechanical coordination number of ca. 3.0. Strong correlations are found between macroscopic and internal variables at the critical state.
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Wang, Jian. "Mechanical Behaviour of Granular Materials in Simple Shear Test Using DEM." Thesis, University of Nottingham, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.517785.
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DeGroot, Don Johan. "The multidirectional direct simple shear apparatus with application to design of offshore Arctic structures." Thesis, Massachusetts Institute of Technology, 1992. http://hdl.handle.net/1721.1/12834.
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Ahmed, Imtiaz 1955. "Investigation of normalized behavior of resedimented Boston Blue Clay using Geonor direct simple shear apparatus." Thesis, Massachusetts Institute of Technology, 1990. http://hdl.handle.net/1721.1/45698.
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Melin, Hanna. "Controlling parameters for normal and shear behaviour of rock fractures-a study of direct shear test data from SKB." Thesis, KTH, Jord- och bergmekanik, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-93976.
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The deep mining and civil engineering industry need to perform rock stability analyses during excavation projects. The stability is mainly controlled by the shear strength of the rock fractures, which are the weakest point of the rock mass. In turn, the shear strength is governed by the mechanical properties of the fractures. It is both time and cost demanding to determine the properties of the rock fractures in laboratory. Also, the interpretation of the results requires a deep understanding of the normal and shear behaviour of rock fractures. This study aims to investigate if it is possible to determine the peak shear strength of rock fractures by merely estimating fracture parameters during field mapping and core logging. SKB supplied test results on drilled bore cores from site investigations in Forsmark and Laxemar for deep nuclear waste deposits. SKB generated data of high quality and in large quantity, which made it very valuable for the purpose of the study. The study begins with a literature review and an interaction matrix, clarifying the relationships between mechanical properties and affecting parameters of rock fractures. The predicted relationships of the parameters are then tested in an analysis based on the compiled data from SKB. The results show that the peak friction angle, the residual friction angle and the dilation angle are possible to approximate for open granite fractures in deep mining projects. Further on, the study proposes that the joint matching coefficient is included in the field mapping and core logging since it has a strong influence on the mechanical behaviour of the fracture, notably the normal and shear stiffness. Finally, the study questions estimations of JRC on small samples.
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McGillivray, Alexander Vamie. "Enhanced Integration of Shear Wave Velocity Profiling in Direct-Push Site Characterization Systems." Diss., Georgia Institute of Technology, 2007. http://hdl.handle.net/1853/19714.
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Enhanced Integration of Shear Wave Velocity Profiling in Direct-Push Site Characterization Systems
Alexander V. McGillivray
370 Pages
Directed by Dr. Paul W. Mayne
Shear wave velocity (VS) is a fundamental property of soils directly related to the shear stiffness at small-strains. Therefore, VS should be a routine measurement made during everyday site characterization. There are several lab and field methods for measuring VS, but the seismic piezocone penetration test (SCPTu) and the seismic dilatometer test (SDMT) are the most efficient means for profiling the small-strain stiffness in addition to evaluating large-strain strength, as well as providing evaluations of the geostratigraphy, stress state, and permeability, all within a single sounding.
Although the CPT and DMT have been in use for over three decades in the USA, they are only recently becoming commonplace on small-, medium-, and large-size projects as more organizations begin to realize their benefits. Regrettably, the SCPTu and the SDMT are lagging slightly behind their non-seismic counterparts in popularity, in part because the geophysics component of the tests has not been updated during the 25 years since the tests were envisioned. The VS measurement component is inefficient and not cost effective for routine use. The purpose of this research is to remove the barriers to seismic testing during direct-push site characterization with SCPTu and SDMT.
A continuous-push seismic system has been developed to improve the integration of VS measurements with SCPTu and SDMT, allowing VS to be measured during penetration without stopping the progress of the probe. A new type of portable automated seismic source, given the name RotoSeis, was created to generate repeated hammer strikes at regularly spaced time intervals. A true-interval biaxial seismic probe and an automated data acquisition system were also developed to capture the shear waves. By not limiting VS measurement to pauses in penetration during rod breaks, it is possible to make overlapping VS interval measurements. This new method, termed frequent-interval, increases the depth resolution of the VS profile to be more compatible with the depth intervals of the near-continuous non-seismic measurements of the SCPTu and the SDMT.
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Campanini, Davide. "Comparison between Direct Tensile and Single Lap Shear for FRCM/SRG composites." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2018. http://amslaurea.unibo.it/17203/.
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Negli ultimi decenni sono state sviluppati nuovi materiali e tecnologie per il rinforzo e la riabilitazione delle strutture esistenti. I sistemi più recenti per il rinforzo esterno ed il recupero strutturale sono materiali compositi costituiti da fibre raggruppate in forma di tessuto ed impregnate ed immerse in una matrice inorganica. Quando il tessuto è composto da fibre di aramide, vetro, basalto, PBO o carbonio, questi compositi sono comunemente definiti Fabric Reinforced Cementitious Matrix (FRCM), mentre, quando il tessuto è fatto da micro-trefoli di acciaio, sono definiti Steel Reinforced Grout (SRG).
In accordo con le rispettive normative, negli Stati Uniti le proprietà meccaniche dei compositi FRCM/SRG si misurano tramite una prova di tensione diretta su provini caricati utilizzando ancoraggi a forcella (clevis grip). In Europa, invece, si ricorre ad una prova di aderenza o single-lap shear su compositi applicati su un substrato cementizio o in muratura.
L’obiettivo di questa tesi è confrontare i risultati ottenuti mediante i due metodi di caratterizzazione sviluppando una campagna sperimentale su due diversi tipi di compositi: un FRCM con fibra di carbonio (CFRCM) e un composito SRG. L’effetto di tre diverse lunghezze di ancoraggio è stato studiato per il sistema CFRCM. L’influenza del numero di strati di tessuto è stata analizzata sia per il sistema CFRCM che SRG considerando uno o due strati.
I risultati mostrano che le differenti condizioni al contorno influenzano in modo significativo la caratterizzazione dei compositi. Per ottenere una misura rappresentativa delle proprietà meccaniche dei compositi FRCM/SRG, è richiesta una lunghezza di ancoraggio sufficiente. Questo studio contribuisce a sviluppare un database sperimentale che consenta la definizione di affidabili protocolli di caratterizzazione. Inoltre, fornisce informazioni rilevanti ai fini progettuali riguardo la lunghezza di ancoraggio adeguate e all’efficacia di applicazioni multistrato.
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Ulmer, Kristin Jane. "Development of an Energy-based Liquefaction Evaluation Procedure." Diss., Virginia Tech, 2020. http://hdl.handle.net/10919/96522.
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Soil liquefaction during earthquakes is a phenomenon that can cause tremendous damage to structures such as bridges, roads, buildings, and pipelines. The objective of this research is to develop an energy-based approach for evaluating the potential for liquefaction triggering. The current state-of-practice for the evaluation of liquefaction triggering is the "simplified" stressbased framework where resistance to liquefaction is correlated to an in situ test metric (e.g., normalized standard penetration test N-value, N1,60cs, normalized cone penetration tip resistance, qc1Ncs, or normalized small strain shear wave velocity, Vs1). Although rarely used in practice, the strain-based procedure is commonly cited as an attractive alternative to the stress-based framework because excess pore pressure generation (and, in turn, liquefaction triggering) is more directly related to strains than stresses. However, the method has some inherent and potentially fatal limitations in not being able to appropriately define both the amplitude and duration of the induced loading in a total stress framework. The energy-based method proposed herein builds on the merits of both the stress- and strain-based procedures, while circumventing their inherent limitations.
The basis of the proposed energy-based approach is a macro-level, low cycle fatigue theory in which dissipated energy (or work) per unit volume is used as the damage metric. Because dissipated energy is defined by both stress and strain, this energy-based method brings together stress- and strain-based concepts. To develop this approach, a database of liquefaction and nonliquefaction case histories was assembled for multiple in situ test metrics. Dissipated energy per unit volume associated with each case history was estimated and a family of limit-state curves were developed using maximum likelihood regression for different in situ test metrics defining the amount of dissipated energy required to trigger liquefaction. To ensure consistency between these limit-state curves and laboratory data, a series of cyclic tests were performed on samples of sand. These laboratory-based limit-state curves were reconciled with the field-based limit-state curves using a consistent definition of liquefaction.Doctor of Philosophy
Soil liquefaction during earthquakes is a phenomenon that can cause tremendous damage to structures such as bridges, roads, buildings, and pipelines. The objective of this research is to develop an energy-based approach for evaluating the potential for liquefaction triggering. Current procedures to evaluate liquefaction triggering include stress-based and strain-based procedures. However, these procedures have some inherent and potentially fatal limitations. The energy-based method proposed herein builds on the merits of both the stress- and strain-based procedures, while circumventing their inherent limitations. The proposed energy-based approach uses dissipated energy (or work) per unit volume to evaluate the potential for liquefaction. Because dissipated energy is defined by both stress and strain, this energy-based method brings together stress- and strain-based concepts. To develop this approach, a database of case histories in which liquefaction was either observed or not observed was assembled. Dissipated energy per unit volume associated with each case history was estimated and a family of relationships was regressed to define the amount of dissipated energy required to trigger liquefaction. Results from a series of cyclic laboratory tests performed on samples of sand were reconciled with the field-based relationships using a consistent definition of liquefaction. This research proposes a method that is based on a robust mechanistic framework that will make it easier to evaluate liquefaction for circumstances that are not well represented in current liquefaction evaluation procedures. The components of the proposed energy-based procedure are developed consistently and are presented in such a way that this procedure can be readily adopted by practitioners who are already familiar with existing liquefaction evaluation procedures. The broader impacts of this work will help to minimize losses from earthquakes by improving the way engineers evaluate liquefaction.
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Echegaray, Oviedo Javier Andrés. "Upgrading the push-off test to analyze the contribution of steel fiber on shear transfer mechanisms." Doctoral thesis, Universitat Politècnica de València, 2014. http://hdl.handle.net/10251/43723.
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The shear behavior of a specimen made of reinforced concrete is complex. The resisting mechanisms are affected by different factors such as section form, slimness of the specimen, longitudinal and transversal reinforcement arrangement, adhesion between concrete and steel, among others. Addition of steel fibers to the concrete improves the ductility as well as the tensile behavior; providing good control during the cracking process. Fibers also enhance the shear behavior of structural elements, increasing ultimate resistance and ductility.
Push-off tests had been used to study the mechanisms of concrete shear transfer. Shear strength of the specimen depends on the contribution of both concrete and reinforcement. Aggregate interlock has a significant contribution to the concrete shear capacity. In the last decades new kinds of concrete have been developed for industrial use, such as high strength concrete (HSC), self-compacting concrete (SCC) or fiber reinforced concrete (FRC), among others. In these new materials aggregate interlock phenomenon may be different when compared to conventional concrete (CC). There is a lack of information in literature about the mechanisms of shear transfer in fiber reinforced concrete elements.Echegaray Oviedo, JA. (2014). Upgrading the push-off test to analyze the contribution of steel fiber on shear transfer mechanisms [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/43723
TESIS
17
Hajdarwish, Ala' M. "Geologic Controls of Shear Strength Behavior of Mudrocks." Kent State University / OhioLINK, 2006. http://rave.ohiolink.edu/etdc/view?acc_num=kent1162259344.
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18
Maghsoudloo, Arash. "Nonlinearity Of The Residual Shear Strength Envelope In Stiff Clays." Master's thesis, METU, 2013. http://etd.lib.metu.edu.tr/upload/12615551/index.pdf.
Full textAbstract:
During shearing of stiff clays, plate-shaped clay particles are parallel-oriented in the direction of shear reaching the minimum resistance of &ldquoresidual shear strength&rdquo
. The residual shear strength envelopes of stiff clays are curved, but for practical purposes represented by linear envelopes. This study investigates the nonlinearity of the residual shear strength envelope using experimental evidence (i) from laboratory reversal direct shear tests on two stiff clays (Ankara clay and kaolinite) at 25 to 900 kPa effective normal stresses and (ii) from laboratory data collected from literature. To evaluate the importance of nonlinearity of the envelope for geotechnical engineering practice, by limit equilibrium method, (a) case histories of reactivated landslides are analyzed and (b) a parametric study is carried out. Conclusions of this study are: (1) The residual shear strength envelopes of both Ankara clay and kaolinite are nonlinear, and can be represented by a power function (cohesion is zero). (2) At least 3 reversals or cumulative 20 mm shear displacement of direct shear box is recommended to reach residual condition. (3) Empirical relations between plasticity index and residual friction angle can accurately estimate the residual strength of stiff clays. (4) Nonlinearity is especially important for landslides where average effective normal stress on the shear plane is less than 50 kPa, both for translational and rotational failures. For such slopes using a linear strength envelope overestimates the factor of safety (more significantly for the case of high pore pressures). (5) As the plasticity index increases, the power &ldquo
b&rdquo
of the nonlinear shear strength envelope decreases, indicating more significant nonlinearity. For less plastic materials, using linear and nonlinear shear strength envelopes does not affect the factor of safety.
19
Oh, Won Taek. "Simple Techniques for the Implementation of the Mechanics of Unsaturated Soils into Engineering Practice." Thesis, Université d'Ottawa / University of Ottawa, 2012. http://hdl.handle.net/10393/23533.
Full textAbstract:
Over the past 50 years, several advancements have been made in the research area of the mechanics of unsaturated soils. These advancements can be categorized into two groups; (i) development (or improvement) of testing techniques (or apparatus) to determine the mechanical properties of unsaturated soils and (ii) development of (numerical, empirical or semi-empirical) models to estimate the variation of mechanical properties of unsaturated soils with respect to suction based on the experimental results. Implementation of the mechanics of unsaturated soils in conventional geotechnical engineering practice, however, has been rather limited. The key reasons for the limited practical applications may be attributed to the lack of simple and reliable methods for (i) measuring soil suction in the field quickly and reliably and (ii) estimating the variation of mechanical properties of unsaturated soils with respect to suction.
The main objective of this thesis research is to develop simple and reliable techniques, models or approaches that can be used in geotechnical engineering practice to estimate sol suction and the mechanical properties of unsaturated soils. This research can be categorized into three parts.
In the First Part, simple techniques are proposed to estimate the suction values of as-compacted unsaturated fine-grained soils using a pocket penetrometer and a conventional tensiometer. The suction values less than 300 kPa can be estimated using a strong relationship between the compressive strength measured using a pocket penetrometer and matric suction value. The high suction values in the range of 1,200 kPa to 60,000 kPa can be estimated using the unique relationship between the initial tangent of conventional tensiometer response versus time behavior and suction value.
In the Second Part, approaches or semi-empirical models are proposed to estimate the variation of mechanical properties of unsaturated soils with respect to suction, which include:
- Bearing capacity of unsaturated fine-grained soils
- Variation of bearing capacity of unsaturated fine-grained soils with respect to matric suction
- Variation of initial tangent elastic modulus of unsaturated soils below shallow foundations with respect to matric suction
- Variation of maximum shear modulus with respect to matric suction for unsaturated non-plastic sandy soils (i.e. plasticity index, Ip = 0 %)
In the Third Part, approaches (or methodologies) are suggested to simulate the vertically applied stress versus surface settlement behavior of shallow foundations in unsaturated coarse-grained soils assuming elastic-perfectly plastic behavior. These methodologies are extended to simulate the stress versus settlement behavior of both model footings and in-situ plates in unsaturated coarse-grained soils.
The results show that there is a reasonably good comparison between the measured values (i.e. soil suction, bearing capacity, elastic and shear modulus) and those estimated using the techniques or models proposed in this thesis research.
The models (or methodologies) proposed in this thesis research are promising and encouraging for modeling studies and practicing engineers to estimate the variation of mechanical behavior of unsaturated soils with respect to matric suction.
20
Iscimen, Mehmet. "Shearing Behavior Of Curved Interfaces." Thesis, Georgia Institute of Technology, 2004. http://hdl.handle.net/1853/7256.
Full textAbstract:
The frictional behavior of soil-construction material interfaces is of significant importance in geotechnical engineering applications such as retaining structures, pile foundations, geosynthetic liners, and trenchless technologies. Since most failures initiate and develop on the interfaces, special attention is required to predict the capacity of these weak planes in the particular application.
Pipe-jacking and microtunneling technologies are being more widely used over the past decade and there is significant interest to predict the jacking forces and jacking distances achievable in order to achieve more efficient design and construction. This study focuses on the evaluation of the frictional characteristics and factors affecting the shear strength of pipe-soil interfaces. Eight different pipes made from fiber reinforced polymer (FRP), polycrete, steel, concrete, and vitrified clay were tested in the experimental program.
For this purpose, a new apparatus was designed to conduct conventional interface direct shear testing on pipes of different curvature. This device allows coupons cut from actual conduits and pipes to be tested in the laboratory under controlled conditions. The apparatus includes a double-wall shear box, the inner wall of which is interchangeable to allow for testing against surfaces of different curvatures. By considering a narrow width section, the circular interface of pipes was approximated with a surface along the axial direction and the boundary is defined by the inner box.
Roughness tests were performed using a stylus profilometer to quantify the surface characteristics of the individual pipes and relate these to the interface shear behavior. The surface topography showed different degrees of variability for the different pipes. To extend the range of roughness values tested and force the failure to occur in the particulate media adjacent to the interface, two artificial pipe surfaces were created using rough sandpapers.
Interface shear tests were performed using the new apparatus with air-pluviated dense specimens of Ottawa 20/30 sand. Additional tests were performed using Atlanta blasting sand to evaluate the effect of particle angularity. The effect of normal stress and relative density were also examined. The interface strength was shown to increase with surface roughness and finally reach a constant value above a certain critical roughness value, which corresponded to the internal strength of the soil itself. This represented the failure location moving from the interface into the soil adjacent to the interface. Both the strength and the shearing mechanism were thus affected by the surface topography. It was also shown that the interface shear strength was affected by particle angularity, relative density and normal stress.
21
Song, Yongxiang. "Réalisation du système triaxial assisté par ordinateur et étude du cisaillement direct 3D pour joints rocheux." Grenoble 1, 1992. http://www.theses.fr/1992GRE10209.
Full textAbstract:
On presente dans cette these un systeme triaxial assiste par ordinateur et un appareillage de cisaillement direct pour joints rocheux. Ce systeme triaxial de revolution est constitue par une presse electromecanique commerciale et deux controleurs pression-volume, ainsi qu'un micro-ordinateur avec une carte d'acquisition (a/n, n/a et e/s). Ce systeme pilote par l'ordinateur peut realiser tous les essais triaxiaux asservis en deformation ou en contrainte, ainsi que des essais cycliques. Un nouvel essai en escalier, draine ou non draine, est presente. Ce type de chemin trouve son interet dans des simulations de comportement pour connaitre des deformations resultant d'increments de contraintes apportes par des ouvrages. Ce systeme developpe recemment est analyse par les resultats des essais et par une comparaison entre deux modes d'asservissement. Quelques criteres sont presentes pour garantir la qualite d'asservissement ainsi que la reussite des essais. La precision du systeme et les facteurs resultant des erreurs sont aussi discutes. Le cisaillement direct pour joints rocheux est en cours de developpement dans la version 2d et sera transforme ulterieurement dans la version 3d. Il est possible de realiser les essais de cisaillement direct en trois modes de sollicitation (axisymetrique, homogeneite cinematique et homogeneite statique). Le principe du projet et le mode d'asservissement sont presentes avec leur calcul
22
Joodi, Benjamin Michael. "Comparative Assessment of Frequency Dependent Joint Properties Using Direct and Inverse Identification Methods." The Ohio State University, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=osu1417024616.
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23
Nam, Soonkie. "Effects of Reservoir Releases on Slope Stability and Bank Erosion." Diss., Virginia Tech, 2011. http://hdl.handle.net/10919/77114.
Full textAbstract:
Reservoir release patterns are determined by a number of purposes, the most fundamental of which is to manage water resources for human use. Managing our water resources means not only controlling the water in reservoirs but also determining the optimum release rate taking into account factors such as reservoir stability, power generation, water supply for domestic, industrial, and agricultural uses, and the river ecosystem. However, riverbank stability has generally not been considered as a factor, even though release rates may have a significant effect on downstream riverbank stability. Riverbank retreat not only impacts land properties but also damages structures along the river such as roads, bridges and even buildings. Thus, reservoir releases need to also take into account the downstream riverbank stability and erosion issues.
The study presented here investigates the riverbank stability and erosion at five study sites representing straight as well as inside and outside channel meander bends located on the lower Roanoke River near Scotland Neck, North Carolina. Extensive laboratory and field experiments were performed to define the hydraulic and geotechnical properties of the riverbank soils at each site. Specifically, soil water characteristic curves were determined using six different techniques and the results compared to existing mathematical models. Hydraulic conductivity was estimated using both laboratory and in situ tests. Due to the wide range of experimentally obtained values, the values determined by each of the methods was used for transient seepage modeling and the modeling results compared to the actual ground water table measured in the field. The results indicate that although the hydraulic conductivities determined by in situ tests were much larger than those typically reported for the soils by lab tests, numerical predictions of the ground water table using the in situ values provided a good fit for the measured ground water table elevation. Shear strengths of unsaturated soils were determined using multistage suction controlled direct shear tests. The test method was validated, and saturated and unsaturated shear strength parameters determined. These parameters, which were determined on the basis of results from both laboratory and field measurements, and the associated boundary conditions, which took into account representative flow rates and patterns including peaking, drawdown and step-down scenarios, were then utilized for transient seepage analyses and slope stability analyses performed using SLIDE, a software package developed by Rocscience. The analyses confirmed that the riverbanks are stable for all flow conditions, although the presence of lower permeability soils in some areas may create excess pore water pressures, especially during drawdown and step-down events, that result in the slope becoming unstable in those locations. These findings indicate that overall, the current reservoir release patterns do not cause adverse impacts on the downstream riverbanks, although a gradual drawdown after a prolonged high flow event during the wet season would reduce unfavorable conditions that threaten riverbank stability.Ph. D.
24
Toufigh, Vahid. "Testing and Evaluation of Confined Polymer Concrete Pile with Carbon Fiber Sleeve." Diss., The University of Arizona, 2013. http://hdl.handle.net/10150/293492.
Full textAbstract:
The goal of this research is to investigate the behavior of polymer concrete confined with a carbon fiber sleeve used as a pile foundation. To evaluate the behavior of a confined polymer concrete pile in this research, four steps was considered. The first step of this investigation considered the mix design of polymer concrete, polymer concrete is a new material which is a combination of epoxy resin and aggregate. Instead of using a traditional mix of cement and water to make concrete, epoxy resin is used. Three dissimilar varieties of aggregate are mixed with different ratios in order to reach the maximum bulk density to obtain the maximum strength. After discovering the optimum ratio which gives the maximum bulk density, several samples of the aggregate are mixed with different ratios of epoxy resin. Next, the samples are investigated in a compression test to observe which ratios have the maximum strength and this ratio is used for a polymer concrete mix design to create a pile foundation. The pile is a built using a cast in place method and confined with a sleeve of carbon fiber. The second part of this investigation determined the structural mechanical properties of confined polymer concrete pile material. The unconfined and confined polymer concrete was tested in compression to determine compressive strength and stress-strain behavior. Similar tests were conducted on unconfined and confined cement concrete for comparison between these materials. Additional tension tests were conducted on unconfined polymer concrete. Then, a carbon fiber sleeve was tested in compression test to determine tensile strength and tension stress-strain behavior. After these tests, the confined polymer concrete is modeled in the computer program MATTCAD which is used to calculate the theoretical bending moment capacity and load-displacement curve. Finally, the confined polymer concrete is tested with the MTS 311 Load Frame in three point load flexure test to determine the experimentally bending moment capacity, load-displacement curve and compare with theoretical results. Confined polymer concrete was tested in one and two way cyclic loading to observe the ductility behavior of this material as laterally loaded piles and compared with cement concrete results in cyclic loading. The third part of this investigation determined the geotechnical mechanical properties of confined polymer concrete pile material. Cyclic Multi Degree of Freedom (CYMDOF) device was used to determine interface reaction and friction angle between confined polymer concrete and soil with interface shear test theory method. Furthermore, the same device was used to determine the friction angle of soil with direct shear test theory, and compare the friction angle results together. The last part of this investigation considered the behavior of different sized confined polymer concrete pile in different types of soil. A confined polymer concrete pile was modeled into PLAXIS and OPENSEES PL computer software to analysis pile in axial load and lateral load respectively. Furthermore, a cement concrete pile was modeled with similar software and conditions to compare these two materials.
25
Huang, He. "Experimental study of NiTi alloy under shear loading over a large range of strain rates." Thesis, Paris 6, 2016. http://www.theses.fr/2016PA066072.
Full textAbstract:
Ce travail décrit une étude expérimentale sur des tôles en Ni-Ti à température ambiante en cisaillement plan simple, et pour des vitesses de déformation de 10-4 à 103/s. En quasi-statique (10-4-10-2/s), la mesure optique du champ de déplacement est indispensable à cause du faible déplacement (0.3mm). Des essais à vitesse de déformation intermédiaire (10-1-101/s) ont été réalisés avec la Machine MTS modifiée, capable d'aller à 300mm/s. Une caméra rapide est nécessaire pour suivre ces tests. Enfin, des barres de Hopkinson sont utilisées pour les essais à haute vitesse (102-103/s).Les efforts se sont concentrés sur la méthodologie afin d'explorer les limites expérimentales. Au niveau mécanique, des efforts ont été apportés sur la conception des montages des mors pour combiner des exigences contradictoires. Au niveau mesure, des caméras optiques fonctionnant jusqu'à 5M images/s ont été utilisées. La texture des images, la peinture, la lumière, la taille d'élément et l'incertitude sont analysées. De plus, la caméra infrarouge est utilisée pour confirmer l'observation optique sous faibles vitesses de déformation.Finalement, des essais ont été réalisés pour 7 ordres de grandeurs de la vitesse de déformation, avec identification de la relation contrainte-déformation et observation de l'évolution de la bande de transformation. On observe : (i) Une augmentation de la contrainte avec la vitesse de déformation. (ii) Un champ de déformation non homogène, même en faible vitesse, avec une bande à 10 degrés par rapport à la direction de cisaillement. (iii) Deux bandes séparées à haute vitesse (102/s), ce qui indique que la bande de localisation dépend de la vitesse de chargementThis work describes an experimental study on a NiTi alloy at the ambient temperature (Pseudoelastic behavior) under the double in-plane shear loading over strain rates from 10-4 to 103/s. Under quasi-static loadings (10-4-10-2/s), the optical full-field measurement is necessary because of the very small displacement (0.3mm). The intermediate loading rates (10-1-101/s) are realized with a modified MTS machine able to load at 300mm/s. Moreover, a high-speed camera is needed to follow such tests. Finally, the Split Hopkinson bars are used to perform tests at impact loading rates (102-103/s).The main effort has been made on the methodological study to explore the experimental possibility. For the mechanical level, the attention has been paid on the design of the clamping system to cope with the contradictory requirements. For the measuring level, different optical cameras with sampling rate till to 5M frames/second are used. The texture, the painting, the lightening, the element size and the uncertainty are analyzed. Furthermore, an infrared camera was used at lower loading rates to confirm the DIC measurement.The tests are continually performed over 7 decades of the strain rate. The nominal stress-strain curves and the detailed observation of the transformation band evolution are measured. The main findings are as follows: (i) Regular stress increase with the strain rate; (ii) an inhomogeneous strain field under in-plane shear condition, even at very low strain rates, with a band at 10 degrees from the shear direction under lower strain rates. (iii) Two separated bands at the strain rate of 102/s, which suggests that the localized transformation bands are rate dependent
26
Festugato, Lucas. "Comportamento de hidratação e resposta cisalhante cíclica de resíduo de mineração cimentado reforçado com fibras." reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2011. http://hdl.handle.net/10183/35605.
Full textAbstract:
As propriedades do solo cotidianamente podem não ser adequadas às características e às necessidades de projeto. É apresentada, como alternativa, a técnica de reforço com inclusão de elementos fibrosos à matriz de solo cimentado e não cimentado. Ainda, embora comuns, o comportamento do solo frente a solicitações cíclicas não é completamente conhecido. Nesse sentido, o estudo do comportamento de hidratação e da resposta cisalhante cíclica de um resíduo de mineração cimentado reforçado com fibras é objetivado. Para tanto, medidas de retração química, medidas de rigidez ao longo da hidratação e ensaios simple shear monotônicos e cíclicos foram realizados com resíduo de mineração cimentado e não cimentado, reforçado com fibras e não reforçado. O resíduo, oriundo da mineração de ouro, um silte arenoso com traços de argila, foi cimentado com diferentes teores de cimento Portland, entre 0% e 10% em relação à massa de solo seco, e reforçado com 0% e 0,5%, em relação à massa de sólidos secos, de fibras de polipropileno de 50mm de comprimento e 0,1mm de espessura, equivalentes a um índice aspecto de 500. Os resultados demonstraram que as fibras não afetaram o processo de hidratação das misturas de resíduo de mineração cimentadas, que apresentam tendência de atenuação logarítmica da retração química com o tempo. Quanto maiores as relações água/cimento, maior o nível de retração química. A inclusão de fibras a misturas de resíduo de mineração cimentadas, da mesma forma, não afetou a evolução dos valores de rigidez inicial, que crescem com tendência logarítmica em função do tempo e aumentam com o acréscimo do nível de cimentação. Sob condições monotônicas de cisalhamento, a adição de fibras conferiu ao material cimentado e não cimentado comportamento de endurecimento. Sob condições cíclicas de deformação cisalhante controlada, as fibras não afetaram a resposta cisalhante das amostras não cimentadas e provocaram aumento dos valores da tensão cisalhante das amostras cimentadas após sucessivos ciclos de esforços. Sob condições cíclicas de tensão cisalhante controlada, a adição de fibras às misturas não cimentadas proporcionou o aumento da resistência aos ciclos de esforços e às misturas cimentadas provocou aumento dos níveis de deformação cisalhante. A concordância das mesmas envoltórias de resistência tanto às trajetórias de tensões dos ensaios monotonônicos quanto às trajetórias dos ensaios cíclicos sob diferentes condições de carregamento possibilitou a obtenção dos mesmos parâmetros de resistência das misturas analisadas sob diferentes condições de carregamento.The soil properties commonly may not suit the project characteristics and requirements. It is presented, as alternative, the improvement technique of fibrous elements inclusion to the cemented and uncemented soil matrix. Moreover, although common, the behaviour of soil under cyclic loads is not completely known. In this sense, the study of the hydration behaviour and the cyclic shear response of fibre reinforced cemented mine tailings is the main objective of this research. Therefore, chemical shrinkage measurements, stiffness measurements during hydration and monotonic and cyclic simple shear tests were conducted on fibre reinforced and unreinforced cemented and uncemented mine tailings. The tailings, produced from gold mining, are classified as a sandy silt with traces of clay and were cemented with different amounts of Portland cement, ranging from 0% to 10% by dry weigh of soil, and reinforced with 0% and 0.5% by dry weigh of solids of polypropylene fibers 50mm long and 0.1mm thick, equivalent to an aspect ratio of 500. The results showed fibres did not affect the hydration process of cemented mine tailings mixtures, which presents logarithmic attenuation of chemical shrinkage over time. The greater the water / cement ratio, the higher the level of chemical shrinkage. The inclusion of fibers to cemented mine tailings, likewise, did not affect the evolution of initial stiffness values, that raise logarithmic over time and increase with the increase of the cementation level. Under monotonic shear conditions, the addition of fibers confers hardening behaviour to the uncemented and cemented materials. Under shear strain controlled cyclic conditions, fibres did not affect the shear response of uncemented samples and increased shear stress values of cemented samples after successive load cycles. Under shear stress controlled cyclic conditions, the fibres addition to the uncemented mixtures increased the resistance to load cycles and to the cemented mixtures increased levels of shearing strain. The agreement of the same strength envelopes to both monotonic and cyclic stress paths, under different cyclic loading conditions, allows the use of the same strength parameters of mixtures analyzed under different loading conditions.
27
Peri, Elena. "An investigation on the behaviour of a shallow foundation resting on a layered soil near a slope." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2016.
Find full textAbstract:
In questo progetto, portato avanti alla University of Western Australia, viene analizzato il comportamento di una fondazione superficiale su un pendio in sabbia sopra un deposito di argilla.
Dopo avere ricavato sperimentalmente i parametri di resistenza di sabbia e argilla, si è proceduto al calcolo con Plaxis 2D della capacità portante della fondazione a striscia sopra questa stratigrafia. I parametri che sono stati considerati in questi modelli sono sia geometrici che di resistenza.
Dopo l'analisi numerica si è elaborata un'equazione che lega capacità portante e tutti i parametri.
Oltre alla parte 2D si è studiata un'applicazione pratica 3D. Con Plaxis 3D si sono calcolati modelli rappresentanti un bulldozer su un pendio in sabbia sopra un deposito di terreno a grana fine.
Anche per questa applicazione si è elaborata un'equazione per ricavare la capacità portante.
28
Errico, Carmine. "Determination of the influence of SRG anchors on the bond behavior of SRG/FRCM strips bonded to a quasi-brittle substrate." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2019.
Find full textAbstract:
The use of FRCM composites (Fiber Reinforced Cementitious Matrix) is becoming more and more widespread. The inorganic matrix guarantees many advantages, especially when dealing with masonry substrates, including a good compatibility from both a physical and a chemical point of view and the lower sensitivity to debonding phenomena at the interface.
Compared to FRP composites, which presents many data in the literature, FRCM composites must be studied in detail and research in this field has only begun in recent years. This work deals with an important problem: the realization of an anchorage system to improve the strength of composites and allow their use even in the absence of adequate development length.
In this study, the effectiveness of the anchorage system and the interaction with an externally bonded FRCM were studied on masonry columns. The columns were tested until failure condition in the Laboratory of Structural and Geotechnical Engineering (DICAM – LISG) of the University of Bologna, via del Lazzaretto 15/5, Bologna.
Test results demonstrate that the introduction of additional anchorages improves the effectiveness of the FRCM composites in terms of resistance and loading capacity.
29
Stewart, Scott William. "Rock mass strength and deformability of unweathered closely jointed New Zealand greywacke." Thesis, University of Canterbury. Civil Engineering, 2007. http://hdl.handle.net/10092/1224.
Full textAbstract:
Closely jointed greywacke rock masses are widespread throughout both the North and South Islands of New Zealand and much of New Zealand's infrastructure is constructed upon greywacke rock masses. This thesis deals with determining the rock mass strength of unweathered closely jointed New Zealand greywacke rock masses. Currently, the estimation of rock mass strength and deformability is reasonably well predicted through the use of such empirical failure criteria as the Hoek-Brown failure criterion and empirical expressions to predict deformability. However, previous studies upon predicting the strength and deformability of unweathered closely jointed New Zealand greywacke rock masses has shown that existing empirical methods of determining strength and deformability are unsatisfactory. The problem with predicting rock mass strength and deformability moduli of New Zealand greywacke and the lack of adequate data to calibrate a failure criterion was the starting point for this work. The objective of this thesis was to increase the knowledge of intact and defect properties of closely jointed greywacke, develop reliable rock mass data with which to calibrate a failure criterion and improve the ability to estimate the rock mass strength of greywacke rock masses. A review of existing failure criteria for rock masses was conducted and of these criteria, the Hoek-Brown rock mass failure criteria was selected to calibrate to both the intact rock and rock mass failure data, because of its broad acceptance in the rock mechanics community. A database of greywacke properties was developed based on previous studies upon unweathered greywacke around New Zealand and is attached to the thesis as an Appendix. The database included descriptions of greywacke defect properties and mechanical properties of the intact rock and joints. From this database, inputs could be justified for numerical modelling and later analyses of failure criteria. Records from the construction archives of the Benmore and Aviemore hydroelectric power projects in the South Island of New Zealand were reviewed to obtain information and results from a series of shear tests carried out on unweathered closely jointed greywacke in the 1960s. Data on rock mass strength at failure and rock mass deformability were extracted from these records to assess the predictability of the failure criterion and deformability expressions. Problems experienced during the shear tests at the Aviemore dam site created doubt as to the actual rock mass strengths achieved at failure. The behaviour of these tests was studied using the finite difference code FLAC. The work was aimed at investigating the potential for transfer of shear force between the two concrete blocks sheared in each test and the impact shear force transfer had upon the likely normal stresses beneath each block at failure. The numerical modelling results indicated that a combination of preferential failure occurring in one direction, and doubt in the actual normal load applied to the concrete blocks during testing lead to premature failure in the blocks sheared upstream. The blocks sheared in the opposite direction failed at normal stresses that are reflective of the strength of an unweathered greywacke rock mass, but these results could be explained by failure occurring along defects therefore not satisfying the assumptions of homogeneity typically required of a rock mass failure criterion. The Hoek-Brown failure criterion for intact rock was investigated by fitting it to the largest intact greywacke datasets. For a full set of test data (i.e. including tensile data), the Mostyn & Douglas (2000) variant of the Hoek-Brown failure criterion gave the best fit for a full set of rock mass data. A multiple regression method was developed which improved the fitted curve to intact data in the tensile region and gave the best estimate of tensile strength if no existing lab results for tensile strength were available. These results suggest that the Hoek-Brown failure criterion is significantly limited in its applicability to intact NZ greywacke rock. Hoek-Brown input parameters different to those suggested by Hoek et al (2002) are recommended for using the Hoek-Brown failure criterion for intact NZ greywacke. For closely jointed NZ greywacke rock masses, the results from the shear tests at Aviemore and Benmore were separated into different GSI classes and Hoek-Brown envelopes fitted to the datasets by multiple regression. Revised expressions were proposed for each Hoek-Brown input parameter (mb, s, ab) as a function of the GSI. The resulting revised Hoek-Brown failure envelopes for NZ greywacke offer a significant improvement on the existing criterion used to predict the strength of NZ greywacke intact rock and rock masses. The differences in the behaviour of the reaction blocks that failed before the test blocks and the reduction in rock strength due to sliding along defects from that predicted could be reasoned from recorded observations and the behaviour of the concrete blocks during the shear tests. This study has clearly illustrated the need for continued research in this area. This includes (1) a means of assessing the role of defects upon the shear strength of closely jointed greywacke rock mass into a failure criterion, (2) further modelling of the in-situ shear tests by a discrete element procedure to expressly determine the role of the defect on failure, (3) more testing on rock masses to obtain more data to calibrate a rock mass failure criterion, and (4) more studies on predicting the strength of extremely disturbed rock masses.
30
Nouailletas, Olivier. "Comportement d'une discontinuité dans un géomatériau sous sollicitations chemo-mécanique - expérimentations et modélisations." Thesis, Pau, 2013. http://www.theses.fr/2013PAUU3038/document.
Full textAbstract:
Ces travaux de thèse s'intéressent à l'étude du comportement d'une discontinuité dans un géomatériau sous sollicitations chemo-mécaniques à l'échelle du laboratoire. Des essais de traction-compression cyclique étudient la refermeture d'une fissure. Ils indiquent que les déformations inélastiques seraient gouvernées en partie par les frottements générés lors du ré-emboîtement des lèvres de la discontinuité, non correspondantes du fait des contraintes internes. Des joints rocheux altérés chimiquement sous sollicitation tangentielle sont étudiés au travers d'essais de cisaillement direct : le comportement des joints dégradés est profondément modifié du fait de la diminution des propriétés mécaniques du matériau de part et d'autre de la discontinuité et de l'accentuation de la non-correspondance des profils rugueux. Le comportement d'une discontinuité est modélisée par le couplage d'un modèle élasto-plastique endommageable continu avec une résolution discrète du problème de contact/frottement (code calcul aux éléments finis Cast3M). Les résultats numériques confirment les phénomènes constatés expérimentalementThis PhD dissertation presents a study aiming at a better understanding of cracks behavior in a geomaterial. The study focuses on the behavior of discontinuities under chemo-mechanical solicitations at the laboratory scale. The mechanical behavior under normal stress is assessed with cyclic tension-compression tests. Experimental data indicate that the inelastic deformations could be partially governed by the friction generated during the closing of the discontinuity lips, and the asperities mismatch is related to the internal stresses. The shear behavior of a rock joint chemically degraded was studied through direct shear tests. Results pointed out significant modifications for altered joints induced by: 1) the mismatch enhancement of the rough profiles of the discontinuity and, 2) the degradation of the mechanical properties of the material on both sides of the discontinuity due to the chemical attack. These experimental results have been used as input data to model the behavior of a discontinuity by the coupling of a continuous elastic-plastic damaged model with a discrete solving of the contact/friction problem. The simulations performed under Cast3M correctly represent the phenomena observed during the experimental testing program
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Nouailletas, Olivier. "Comportement d'une discontinuité dans un géomatériau sous sollicitation chemo-mécanique : expérimentations et modélisations." Thèse, Université de Sherbrooke, 2014. http://savoirs.usherbrooke.ca/handle/11143/110.
Full textAbstract:
Résumé : Ces travaux de thèse s'intéressent à l'étude du comportement d'une discontinuité dans un géomatériau sous sollicitations chemo-mécaniques à l'échelle du laboratoire. Des essais de traction-compression cyclique étudient la refermeture d'une fissure. Ils indiquent que les déformations inélastiques seraient gouvernées en partie par les frottements générés lors du ré-emboîtement des lèvres de la discontinuité, non correspondantes du fait des contraintes internes. Des joints rocheux altérés chimiquement sous sollicitation tangentielle sont étudiés au travers d'essais de cisaillement direct : le comportement des joints dégradés est profondément modifié du fait de la diminution des propriétés mécaniques du matériau de part et d'autre de la discontinuité et de l'accentuation de la non-correspondance des profils rugueux. Le comportement d'une discontinuité est modélisée par le couplage d'un modèle élasto-plastique endommageable continu avec une résolution discrète du problème de contact/frottement (code calcul aux éléments finis Cast3M). Les résultats numériques confirment les phénomènes constatés expérimentalement.//Abstract: To probate the technology of CO[indice inférieur 2] geological storage, the integrity of the site must be assure over time. This industruial problematic involves the study of the mechanical properties alteration of geomaterials in the presence of CO[indice inférieur 2]. The scenario at the origin of this thesis illustrates the possibility of a CO[indice inférieur 2] leakage on a fault located in the caprock. This geological problem is complicated by the many parameters to consider: in situ temperature and pressure, scale effect, heterogeneities of the geomaterial, geofluide composition, chemical reactions ... These works focus on the behavior of a discontinuity in a geomaterial solicited chemomechanically at the laboratory scale. They were realised in cotutelle between SIAME laboratory at the University of Pau and Pays de l'Adour (France) and the laboratory of rock mechanics and engineering geology from the University of Sherbrooke (Quebec, Canada). The first part of the experimental program was defined to characterize the reclosing of a crack under cyclic uniaxial stress. The second experimental campaign has studied the shear behavior of a rock joint chemically degraded. The data obtained were used to model the behavior of a discontinuity by the finite element method. The mechanical behavior of a crack under normal stress is assessed with cyclic tension-compression tests. Stress curve showed hysteresis during opening and closing cycles of a discontinuity in concrete, it indicated inelastic deformations The analysis of displacement field by image correlation indicated that theses deformations were partially governed by the friction generated during the closing of the discontinuity lips. Frictional phenomena are due to asperities mismatching induced by the internal stresses in the concrete. The shear behavior of a rock joint chemically damaged was studied through direct shear tests. Rough surfaces were immersed in acid solution during 6 hours at constant pH. Digitalization of these surfaces befor and after immesion, with a lase profilometer, indicates little modifications of the geometry induced by dissolution of material. Results of tests pointed out significant modifications for altered joints illustred by a of the peak shear strength and an increased of contractancy. They are induced by: 1) the mismatch enhancement of the rough profiles of the discontinuity and, 2) the degradation of the mechanical properties of the material on both sides of the discontinuity due to the chemical attack. Numerical contribution of the thesis lies in modeling the behavior of a discontinuity by the coupling of an continuous elastic-plastic damaged model with a discrete resolution of the contact/friction problem. The model is developed with the finite element code Cast3M. Geometries lips discontinuities are modeled directly from the roughness profiles from experimental scans. The numerical results correctly represent the friction phenomena observed experimentally. Finally, a model of the shear test altered joints is performed by coupling the mechanical model with chemical damage model.
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Reis, Jeselay Hemetério Cordeiro dos. "Modelo de atrito estático em interfaces de contato entre concreto e areia." Universidade de São Paulo, 2006. http://www.teses.usp.br/teses/disponiveis/18/18132/tde-17072006-111343/.
Full textAbstract:
Esta tese apresenta os princípios e a formulação de um modelo não-linear de atrito estático em interface de concreto areia. A hipótese básica para desenvolvimento das equações consiste na ocorrência do atrito de deslizamento (atrito verdadeiro), do atrito de rolamento (rearranjo das partículas) e da dilatância (variação de volume durante o cisalhamento). A solução analítica do modelo considera o efeito da rugosidade da superfície de contato, da curva granulométrica da areia e do seu estado de compacidade inicial. Foram realizados ensaios de cisalhamento direto com carga normal constante em interface de contato entre concreto e areia com seção de 500 mm x 500 mm com o objetivo de permitir a calibração do modelo proposto. É discutida e sugerida a incorporação da equação constitutiva desse modelo em análises de interação solo-estrutura via método dos elementos finitos. Sua aplicabilidade é demonstrada através da análise 1D e 2D de estacas de atrito executadas em areia e submetidas a carregamentos de compressãoThis thesis presents the principles and formulation underlying a concrete-sand interface nonlinear static friction model. The basic hypothesis employed in the development of the model equation takes into account the interface sliding friction (true friction), a rolling friction (particle rearrangement) and dilatancy(volume variation during shear). The model analytical solution considers the effect of roughness of the contact surface, the grain size distribution and its initial state of compactness of the sand. To calibrate the proposed model, a direct shear stress test under constant load was carried out along a 500mm x 500mm section concrete-sand interface. Furthermore, a discussion and suggestion of the inclusion of the model constitutive equation applied to the analysis of soil-structure interaction using the finite element method are presented. The applicability of the proposed model is proven through the analysis of 1-D and 2-D skin friction piles made of sand mass subjected to compression load
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Nouailletas, Olivier. "Comportement d'une discontinuit?? dans un g??omat??riau sous sollicitation chemo-m??canique : exp??rimentations et mod??lisations." Thèse, Universit?? de Sherbrooke, 2014. http://savoirs.usherbrooke.ca/handle/11143/110.
Full textAbstract:
R??sum?? : Ces travaux de th??se s'int??ressent ?? l'??tude du comportement d'une discontinuit?? dans un g??omat??riau sous sollicitations chemo-m??caniques ?? l'??chelle du laboratoire. Des essais de traction-compression cyclique ??tudient la refermeture d'une fissure. Ils indiquent que les d??formations in??lastiques seraient gouvern??es en partie par les frottements g??n??r??s lors du r??-embo??tement des l??vres de la discontinuit??, non correspondantes du fait des contraintes internes. Des joints rocheux alt??r??s chimiquement sous sollicitation tangentielle sont ??tudi??s au travers d'essais de cisaillement direct : le comportement des joints d??grad??s est profond??ment modifi?? du fait de la diminution des propri??t??s m??caniques du mat??riau de part et d'autre de la discontinuit?? et de l'accentuation de la non-correspondance des profils rugueux. Le comportement d'une discontinuit?? est mod??lis??e par le couplage d'un mod??le ??lasto-plastique endommageable continu avec une r??solution discr??te du probl??me de contact/frottement (code calcul aux ??l??ments finis Cast3M). Les r??sultats num??riques confirment les ph??nom??nes constat??s exp??rimentalement.//Abstract: To probate the technology of CO[indice inf??rieur 2] geological storage, the integrity of the site must be assure over time. This industruial problematic involves the study of the mechanical properties alteration of geomaterials in the presence of CO[indice inf??rieur 2]. The scenario at the origin of this thesis illustrates the possibility of a CO[indice inf??rieur 2] leakage on a fault located in the caprock. This geological problem is complicated by the many parameters to consider: in situ temperature and pressure, scale effect, heterogeneities of the geomaterial, geofluide composition, chemical reactions ... These works focus on the behavior of a discontinuity in a geomaterial solicited chemomechanically at the laboratory scale. They were realised in cotutelle between SIAME laboratory at the University of Pau and Pays de l'Adour (France) and the laboratory of rock mechanics and engineering geology from the University of Sherbrooke (Quebec, Canada). The first part of the experimental program was defined to characterize the reclosing of a crack under cyclic uniaxial stress. The second experimental campaign has studied the shear behavior of a rock joint chemically degraded. The data obtained were used to model the behavior of a discontinuity by the finite element method. The mechanical behavior of a crack under normal stress is assessed with cyclic tension-compression tests. Stress curve showed hysteresis during opening and closing cycles of a discontinuity in concrete, it indicated inelastic deformations The analysis of displacement field by image correlation indicated that theses deformations were partially governed by the friction generated during the closing of the discontinuity lips. Frictional phenomena are due to asperities mismatching induced by the internal stresses in the concrete. The shear behavior of a rock joint chemically damaged was studied through direct shear tests. Rough surfaces were immersed in acid solution during 6 hours at constant pH. Digitalization of these surfaces befor and after immesion, with a lase profilometer, indicates little modifications of the geometry induced by dissolution of material. Results of tests pointed out significant modifications for altered joints illustred by a of the peak shear strength and an increased of contractancy. They are induced by: 1) the mismatch enhancement of the rough profiles of the discontinuity and, 2) the degradation of the mechanical properties of the material on both sides of the discontinuity due to the chemical attack. Numerical contribution of the thesis lies in modeling the behavior of a discontinuity by the coupling of an continuous elastic-plastic damaged model with a discrete resolution of the contact/friction problem. The model is developed with the finite element code Cast3M. Geometries lips discontinuities are modeled directly from the roughness profiles from experimental scans. The numerical results correctly represent the friction phenomena observed experimentally. Finally, a model of the shear test altered joints is performed by coupling the mechanical model with chemical damage model.
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Ourahmoune, Reda El Hak. "Contribution à la compréhension de la fonctionnalisation mécanique de surface des composites à matrice thermoplastique (PEEK) destinés à l'assemblage par collage." Phd thesis, Ecole Centrale de Lyon, 2012. http://tel.archives-ouvertes.fr/tel-00838760.
Full textAbstract:
L'assemblage des matériaux composites thermoplastiques tel que le PEEK est l'une des problématiques majeure de l'industrie aéronautique. Actuellement, différentes techniques sont développées pour assurer l'assemblage structural de ces matériaux, tels que : le soudage, le rivetage, le boulonnage et le collage. Les enjeux industriels majeurs sont principalement, à l'heure actuelle, la conception des structures simplifiées au maximum afin de réduire les coûts de production et la réduction des consommations énergétiques. A cet effet, l'industrie aéronautique fait fréquemment appel à l'assemblage par collage en raison de nombreux avantages qu'il offre (gain de poids, distribution régulière des contraintes, absence de trous) par rapport aux autres techniques existantes. Le PEEK (PolyEtherEtherKetone), est un matériau polymère semi-cristallin thermoplastique, à hautes performances. Ce matériau est souvent utilise dans l'industrie aéronautique principalement renforce par des fibres de carbone ou de verre. Cependant, du fait du niveau élevé de sa résistance chimique l'assemblage par collage du PEEK et de ses composites nécessitent des traitements de surfaces appropries et optimises. Or, afin d'obtenir un system collé à haute performance, la problématique scientifique et technique doit être concentrée sur la jonction entre les éléments à assembler. En effet, la qualité de cette jonction est de la plus haute importance car elle doit permettre un transfert optimal des contraintes thermomécaniques lorsque l'assemblage est soumis a ses conditions d'usage. Cette étude concerne donc, l'amélioration des propriétés mécaniques (monotones et cycliques) de l'assemblage par collage PEEK/PEEK. Dans cette optique, un traitement de surface simple de mise en œuvre est proposé. Ce traitement est le sablage, qui permet la modification topographique (morphologique) de surface. La compréhension des différents phénomènes d'interaction aux interfaces intervenant dans l'amélioration du comportement mécanique du joint de colle et qui s'inscrit dans la triptyque : " Rhéologie, Physico-chimie et topographie ", est l'enjeu scientifique majeur dans cette thèse. Dans un premier temps, l'influence des paramètres du traitement tels que le temps de projection, la taille des particules, sur la morphologie de surface de différents matériaux à base de PEEK a été analysée, permettant ainsi d'établir la corrélation entre les paramètres morphologiques et les mécanismes de modification topographique de surface intervenant pendant le traitement de surface. L'un des facteurs clefs pour la compréhension des mécanismes d'interaction entre l'adhésif liquide et le substrat solide est la mouillabilité. L'analyse du comportement au mouillage en fonction des différents paramètres du traitement a été réalisée. La mouillabilité des surfaces traitées est fortement affectée par la rugosité de surface créée après ce traitement. La relation entre les paramètres morphologiques et la mouillabilité a été discutée. Enfin, l'influence des paramètres du traitement par sablage sur le comportement mécanique monotone et à long terme (essais de fatigue) sur la résistance du joint colle a été étudié à l'aide d'essais de cisaillement sur éprouvettes à simple recouvrement. Ceci a conduit, à la proposition de paramètres morphologiques surfaciques spécifiques pour l'optimisation du comportement mécanique du joint de colle des matériaux composites à matrice PEEK.
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Cocheteau, Natacha. "Caractérisation et modélisation d'une adhérence moléculaire renforcée." Thesis, Aix-Marseille, 2014. http://www.theses.fr/2014AIXM4700/document.
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Le collage par adhérence moléculaire est un collage basé sur la mise en contact de deux surfaces sans l'utilisation de colle ou matériaux additionnels. Ce procédé de collage est utilisé dans de nombreuses applications, notamment dans les domaines de l'optique terrestre et spatiale. Bien qu'un prototype ait déjà passé avec succès l'environnement spatial - où les contraintes d'utilisations sont différentes de celles rencontrées sur Terre - la spatialisation de cette technologie nécessite une caractérisation plus fine du procédé ainsi qu'une amélioration de la tenue mécanique des interfaces adhérées afin de valider les normes de l'Agence spatiale Européenne. Pour répondre à cette problématique de spatialisation de la technologie, des essais mécaniques ainsi que des analyses chimiques ont été réalisés dans le but d'étudier l'influence de certains paramètres du procédé ) sur la tenue mécanique et l'énergie de collage. Ces essais ont également été réalisés afin de comparer les deux matériaux étudiés : le verre de silice et le Zérodur vis-à-vis de l'adhésion. A l'issue de ces essais, les paramètres à appliquer permettant de doubler la tenue mécanique des interfaces adhérées ont été déterminés. Parallèlement, une loi phénoménologique reliant l'énergie de collage aux précédents paramètres du procédé a été développée ainsi qu'un modèle macroscopique visant à décrire l'intensité d'adhésion. Ces deux modèles une fois couplés permettent de modéliser le comportement normal de l'interface en fonction des paramètres du procédé. Enfin, ces deux lois sont implémentées dans un code éléments finis afin de simuler la propagation de la fissure lors de l'essai de clivage au coinDirect bonding consists in joining two surfaces without the use of any adhesive or additional material. This process is used in several applications, particularly in terrestrial and spatial optics. Although a prototype passed with success spatial environment - where constraints involved are very different from those encountered on Earth - this technology requires a more detailed characterization and an improvement of the mechanical strength of bonded interfaces in order to validate the European Space Agency standards. To address this issue, mechanical tests (double shear tests, cleavage tests and wedge tests) and chemical analysis (wetting tests and XPS spectroscopy) were performed in order to study the influence of some process parameters (roughness, relative air humidity during room temperature bonding, the annealing temperature and time) on the mechanical strength and the bonding energy. These tests compared the two materials used: fused silica glass and Zerodur glass. As a result of these tests, optimal parameters doubling the mechanical strength were also obtained. In the same time, a phenomenological law relating the bonding energy to the previous parameters is developed as well as a macroscopic model to describe the adhesion intensity. Both models when coupled describe the normal behavior of the bonded interface depending on the process parameters. Then, the both laws are implemented in a finite elements model in order to simulate the crack propagation during the wedge test
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Tseng, Hsiao-Chian, and 曾孝欽. "Development of a Multi-Purpose Shear Test System for Soft Rocks-Direct shear and Simple Shear Apparatus." Thesis, 2003. http://ndltd.ncl.edu.tw/handle/11754689634744927071.
Full textAbstract:
碩士國立交通大學
土木工程系
91
Development of a Multi-Purpose Shear Test System for Soft Rocks - Direct Shear and Simple Shear Apparatus Student: Hsiao-Chian Tseng Advisor： Dr. Jyh-Jong Liao Dr. Yii-Wen Pan Department of Civil Engineering National Chiao Tung University Abstract Due to the low strength and high deformability of poorly cemented sedimentary rocks, the conventional soil or rock mechanics test equipments are not suitable for determining the mechanical properties of those rocks. In order to propose reasonable engineering approaches in the soft rock area, the mechanical behavior of the rocks has to be investigated in details. To study the mechanical behavior of soft rocks, we need to develop a test system, which is appropriate for testing soft rocks. The geotechnical group, NCTU, aims to develop a multi-purpose shear test system for soft rocks. The system can perform direct shear test, simple shear tests, torsional shear tests, and triaxial tests. This thesis has designed and built a servo-controlled shear apparatus including direct shear test and simple shear test apparatus. The maximum normal and shear capacity of the system are 20 tons and 10 tons, respectively. The equipment was designed to conduct direct shear and simple shear tests under various conditions including constant normal force, constant normal displacement, and constant stiffness, especially for soft rock specimen. A series of experiments were carried out to verify the design objectives. It was confirmed the designed equipment could be operated according to the designed purposes. Keywords : soft rock, direct shear, simple shear, multi-purpose shear test system.
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Gao-zhi-hua and 高志華. "To investigate the feasibility of using the large size simple shear test device to replace the direct shear test device." Thesis, 1999. http://ndltd.ncl.edu.tw/handle/08868719282222088171.
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碩士朝陽大學
營建工程系碩士班
87
Abstract Gravel formation is widely distributed in the central region of Taiwan. The difficulties of under ground excavation in gravel layers will be encountered in the construction of several large transportation projects. In the design of lateral earth pressure for the supporting system of under ground excavation, he shear strength parameters are the most important property to be obtained. Therefore, how to find out the mechanical strength parameters of gravel layer promptly and correctly is one of the most important research topic in geotechnical engineering. Previous study indicates that the distribution of stress and strain is more uniform in a simple shear device then in a direct shear device. Therefore, a new apparatus which can perform tilt table test, direct shear test, as well as simple shear test was designed in this study to investigate the influence of testing methods on the shear strength of gravel, and the feasibility of using direct simple shear test instead of direct shear test for obtaining the shear strength parameters of gravel. Results of this study indicate that at low normal stresses, due to the effects of stacking the shear strength of samples with largest grain diameter equal to 3-inches is higher than the strength of sample with smaller grain size. However, this trend is less significant at higher normal stresses. It also shows that for duplicated samples under the same normal stress, because the simple shear test does not force the sample to be failed along a pre-defined failure plane, the shear strength obtained from simple shear test is less scatter then results from direct shear test.
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Jang, Hung-Yu, and 簡弘雨. "Shear Strength of Remolded Clay determined from NGI Direct Simple Shear Device." Thesis, 1995. http://ndltd.ncl.edu.tw/handle/70613993813694841179.
Full textAbstract:
碩士國立臺灣科技大學
營建工程技術學系
83
A series of simple shear test has been performed on the remolded Taipei silty clay with the Norwegian Geotechnical Institute (NGI) direct simple shear device. Test results indicate that the stress-strain relationship of Taipei silty clay can be normalized with the effective consolidation pressure when tested under different over-consolidation ratios (OCR) and a simple constitutive equation can be adopted to fit the test results. The undrained shear strength at different depths can be determined from the relationship between the normalized undrained strength ( Su / σ '''' vc ) and the OCR values established following the SHANSEP method. If considering the strain compatibility along a slope slip surface, the stress-strain relationships obtained from the CAUC and CAUE triaxial tests are either significantly larger or smaller than the average value due to the progressive failure and the material anisotropy. However, it is found in this study that the average stress-strain behavior can be quite accurately predicted by the simple shear result.
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Lin, Yu-Chun, and 林郁鈞. "Numerical simulation in direct shear test using bonded particles." Thesis, 2014. http://ndltd.ncl.edu.tw/handle/36549517862215088518.
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碩士國立中央大學
土木工程學系
102
Direct shear testing is among the most common laboratory tests for obtaining the engineering properties of soils. However, the microscopic behavior during direct shear test of this type of material is not always easy to monitor. Previous studies have found that the non-uniformity of the stress can be developed along the failure plane have been brought up by previous study. Therefore, a discrete element method is employed and the PFC2D is used to simulate the direct shear test in this study. Since prior researchers have been observed the influenced of the microscopic parameters and the microscopic behavior of the dry granular material during the direct shear test, I simulate the direct shear test by bonded-particle and investigate the related of the particles microscopic parameters and the macroscopic cohesion and friction angle in this study. I also monitor stress and porosity distribution, and bond break condition during direct shear test as well as analyze the variations of average stress, stress path and major principal plane along the pre-determined failure plane were also observed. The following summaries are addressed: (1) smaller particles size has stronger cohesion and smaller friction angle, and greater bond forces have stronger cohesion; (2) the dilation of the overall particle assembly comes from the right of the upper shear box and left of the lower shear box; (3) most breaks of the bonds locate on the shear zone, and the number of normal bonds breaks exceeds that of the shear bonds breaks; (4) the directions of major principal plane ranges from 50 and to 60 degrees in the counterclockwise direction until the test specimen reaches failure; (5) the coefficients of variation of the horizontal and vertical stress become larger when near approaching the failure, and the coefficient of variation of the shear stress becomes smaller and more stable.
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Ye, Jhen-You, and 葉真有. "A study of geogrid interface shear behavior by large-scale direct shear test." Thesis, 2009. http://ndltd.ncl.edu.tw/handle/21664813673372125079.
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碩士國立暨南國際大學
地震與防災工程研究所
97
The interface friction coefficient between different soils and geosynthetics by obtaining from large-scale direct shear test has been widely used in designing of reinforced earth structure. Most of the direct shear tests are usually performed the geogrid and same soil at upper and lower layer of shear box. The lack of research by using direct shear test to observe the shear band of soil particles. Therefore this study adopt a transparent large-scale direct shear box with five opening size of grid and four different soil particle size to observe the flow characeteristics of soil particle at interface shear band by using a digital camera. Recording interface friction changes and analyize the change of different geogrid characteristics and between soil particles. The testing results show gravel particles and geogrid have good interaction behavior. Failure surface of shear band will be far away from the location of geogrid and interface area. The bandwidth is about (9.2mm-26mm)、(8.7mm-13.4mm) that is measured at Vietnam sand. The interface shear band bandwidth is about (4mm-6mm) at Ottawa sand and gravel. Observation of Ottawa sand interface shear band bandwidth about (1.2mm-2.6mm),effect of sand particle size on the interface shear band with the scope of the smallest. The result of interface shear observation use four different soil particle size and five different kinds of type geogrid of the above mentioned, the interface shear band ranked in descending order are as follows: gravel＞Vietnam sand＞Ottawa sand. Understandably, the different soil particle size can show the different interface behavior, despite in reinforced soil condition or in unreinforced soil condition, gravel specimen has more visible shear band than Vietnam sand and Ottawa sand. Under the same conditions, the gravel has the higher shear strength more than Vietnam sand and standard sand, soil dilation behavior also more pronounced. This study is to explore Interface shear observation and to understand the soil in the geogrid rib development, in this test can found that geogrid surface and geogrid rib tensile strength with soil particle mobile has the quite Obviously influence.
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McGuire, Seth T. "Comparison of direct simple shear confinement methods on clay and silt specimens." Thesis, 2011. http://hdl.handle.net/10945/24345.
Full textAbstract:
CIVINSASTM D2435 (2000) allows for both Teflon coated stacked rings and wire reinforced membranes to be used as confinement methods in direct simple shear (DSS) testing of soils. Although stacked rings were developed over 50 years ago, wire reinforced membranes have been used almost exclusively in practice. Over the past 10 years, however, stacked rings have become more popular and are now the dominant confinement system sold and used in the United States. Despite this change, no comprehensive testing program comparing both confinement methods has been published. The objective of this thesis is to perform a laboratory testing program to compare the results of using stacked rings and wire reinforced membranes as a confining system for direct simple shear tests. Tests were performed on samples of a high plasticity clay from the Gulf of Mexico, a low plasticity organic silt from Rhode Island, and a low plasticity sensitive clay from Portland, Maine.
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Sung, chiu-yen, and 宋丘言. "Discrete Element Modeling of Granular Material in Direct Shear Test." Thesis, 2012. http://ndltd.ncl.edu.tw/handle/31759052501309765061.
Full textAbstract:
碩士國立中央大學
土木工程研究所
100
Direct shear test has been among common laboratory tests to obtain the engineering properties of soils, especially for dry granular soils. In this study, the microscopic parameters to describe the force-displacement relationship between particles are compared to the macroscopic engineering properties of the particle assemblies. It was found that the friction angle of the particle assembly is related to the contact normal and shear stiffness and the particle friction from a microscopic point of view. Dilation of the particle assembly is also observed in the discrete element model. Basically the dilation of the overall particle assembly comes from the dilation of the particles in the shear zone. Furthermore, the non-uniformity of stress states along the predetermined failure plane is examined. As the normal stress increases, the stress state in the middle of the predetermined shear plane also becomes less complicated with pure compression loading, while for the smaller normal stress, the stress states are combinations of compression and extension loading. The variations of stress path somehow also explains why a direct shear test can overestimate the strength of a granular material, since a compression loading test can yield the highest strength comparing to other test types.
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Pi-Chih, Hsieh, and 謝碧枝. "The Study of Direct Shear Test Method on Unsaturated Soil." Thesis, 2013. http://ndltd.ncl.edu.tw/handle/06429798274174156312.
Full textAbstract:
碩士明新科技大學
土木工程與環境資源管理系碩士班
101
The ground water exists in nature environment. The soil below ground water table, immerged in water long period of time, is called saturated soil. Due to capillary effect, rainwater infiltration and evaporation, the soil underground water table exhibits native pore water pressure, it is called unsaturated soil. The research of traditional soil mechanics on saturated soil had well developed and results were vigorous. Because of expensive equipment, difficulty of test technics and sensitive of test precision, the study in the field of unsaturated soil is still limited. Minghsin University of Science and Technology locate at Hukou terrace, the ground water table is at -5 meters below ground surface. The soil above the ground water table, dried and wetted altered frequently, is in unsaturated condition. This study tries to apply traditional direct shear test method and contact filter paper method to remodel lateritic soil sample. The relationship between unsaturated soil shear strength and matric suction is studied. The results show that the direct shear behavior of unsaturated soil reveal shear dilation properties, the lower of soil water content, the larger of dilatancy angle. The relative shear strength shows the same effect. Soil matric suction is inverse proportion to soil moisture content. The relationship between soil matric suction and unsaturated soil shear strength is increased nonlinearly. The suggest test method successes apply in unsaturated soil.
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JOU, Hung-Sheng, and 周鴻昇. "Sand-Behavior Study in Constant Volume Test and Undrained Test on NGI Simple Shear Apparatus." Thesis, 1994. http://ndltd.ncl.edu.tw/handle/60293128434547307835.
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Rutherford, Cassandra Jane. "Development of a Multi-directional Direct Simple Shear Testing Device for Characterization of the Cyclic Shear Response of Marine Clays." Thesis, 2012. http://hdl.handle.net/1969.1/ETD-TAMU-2012-05-10743.
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This dissertation describes the development of a new multi-directional direct simple shear testing device, the Texas A&M Multi-directional Direct Simple Shear (TAMU-MDSS), for testing marine soil samples under conditions, which simulate, at the element level, the state of stress acting within a submarine slope under dynamic loading. Prototype testing and an experimental program to characterize the response of marine clays to complex loading conditions are presented. The work is divided into four major components: 1) Equipment Development: Design and construction of a prototype multi-directional direct simple shear testing device (TAMU-MDSS) that addresses the limitations of previous devices. 2) Support systems: selection of control software, development of data acquisition system and design of back pressure systems for direct pore pressure measurements. 3) Prototype Testing: performance of the TAMU MDSS system and testing of strain-control and stress-control capabilities. 4) Experimental Testing: characterize the response of marine clays to monotonic, dynamic and random loads. The two-directional monotonic, cyclic, circular and figure-8 tests demonstrated the undrained shear strength increases with increasing initial shear stress, (i.e, slope), for shearing in the same direction (equivalent to downhill). The strength decreases for shearing in the direction opposite to the initial stress (shearing uphill). The response is as brittle for shearing in the same direction as the shear stress applied during consolidation initial shear stress and ductile for shearing opposite to initial shear stress. These findings have important implications for the stability of the slope, predicting that forces acting downward in the slope direction will need to mobilize less strain to reach peak strength and initiate failure. This information provides insight into the behavior of marine soils under complex loading conditions, and provides high quality laboratory data for use in constitutive and finite element model development for analysis of submarine slopes.
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Nien, Wei-Tung, and 粘為東. "Using PFC2D to Simulate the Shear Zone in a Direct Shear Test and its Application." Thesis, 2010. http://ndltd.ncl.edu.tw/handle/30094935235602572839.
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碩士臺灣大學
土木工程學研究所
98
Engineers are accustomed to using finite element method (FEM) to simulate the failure problem in sand. In this way, however, they are unable to solve the case with rapture and rolling. In order to analyse the real stress and strain situation in soil, more and more researchers choose to use distinct element method (DEM) to simulate the physics experiment and field problem. Nevertheless, the shear zone localization is still a significant issue to be further studied. In order to localize the shear zone, this research simulates the most basic soil experiment, direct shear test, by using a DEM software PFC2D, trying to propose a method which can point out the shear zone location. According to a structural geologic analysis method recommended by Ramsay and Huber (1983), this study defines the homogeneous strain in the soil by ellipticity R. R is a relative physical quantity to shear strain γ which is more familiar to engineers. Then this study set many grid points in the direct shear test simulation, separating the simulating soil into several squares with same area size. Every square is a shear strain calculating unit named grid square. The shear strain can be regarded as homogeneous if the grid square is small enough, and then the shear strain of the grid square can be represented by the ellipticity R. Combining two definition mentioned above, we can calculate the shear strain of every single grid square. Then, it is clear to localize the shear zone by giving every square different color related to its shear strain. Finally, this study also localize the shear zone in the fault sand box simulation and land slide simulation, and compare the result in the fault sand box in this study with the research studied by Chung (2007). No program can calculate the ellipticity in PFC2D, so in this study matrix calculating software MatLab is used to develop a program that can solve this problem. The simulation results indicate that the shear zone in the direct shear test is horizontal and its shape looks like lens. Also, particle rolling inside the shear zone can be observed. In the fault sand box simulation, the result demonstrates the development of the shear zone and the fault tip of tri-shear zone. In the land slide simulation, the result demonstrates the development of sliding surface and the appearance of tension crack.
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Chi, Yu-Cheng, and 紀有政. "A Study of Unsaturated Consolidated Drained Shear Strength for Weathered Mudstone by Direct Shear Test." Thesis, 2015. http://ndltd.ncl.edu.tw/handle/76817869175221745719.
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碩士國立高雄第一科技大學
營建工程研究所
103
In the dry season, mudstones are just as hard as rocks. In the raining season, however, mudstones absorb excessive water, causing mudstones to swell and disintegrate. As a result, slopes are uncovered. Between underground water and topsoil are unsaturated mudstones. With its matric suction, the unsaturated mudstones stabilize soil firmly in the dry season. However, mudstones lose matric suction in the raining season due to the infiltration of rainwater. As a result, mudstones lose shear strength. With the decreased shear strength, the shallow layer of slope collapses or slides. This study gathered soil samples from a slope nearby the mire volcano in Moon World, Tainliao District, Kaohsiung. Several tests were conducted to identify the basic physical properties of soil samples with emphasis on the characteristics of the weathered mudstone in Tianliao District. Therefore, in-situ moisture content was simulated; remolded specimens were reproduced; the relationship between the matric suction, saturation, and moisture content of weathered mudstone was analyzed using soil water characteristic curve; saturated consolidated drainage direct shear test was conducted using the modified direct shear apparatus developed by National Kaohsiung First University of Science. Five levels of matric suction, namely, 50, 100, 150, 250, and 350kPa, were designated for the unsaturated consolidated drainage direct shear test in which net normal stress was set as 100, 200, and 400kPa, respectively. The test was designed to identify the rise and fall of shear strength due to the changes of moisture content in connection with the varying matric suction of the weathered mudstone in Tianliao District. Gathered from the surface layer of weathered soil, the soil samples were considerably porous with a few soil particles. According to the soil water characteristic curve, the soil has an unsatisfactory water-keeping effect. According to the consolidated drainage test, the sample soil has 43.4kPa of effective cohesion force and 22.6° of inner friction angle. Moreover, the unsaturated consolidated drainage test indicated that the inner friction angles within all levels changed slightly. Using average inner friction angle 23.5° as the shear strength, this study concluded that the matric suction could change the moisture content of the soil samples, causing the soil shear strength to increase as the matric suction increases. Moreover, a non-linear relationship between matric suction and total cohesion force was identified through the test. Based on the non-linear relationship stated above, the angle〖 ϕ〗^b corresponding to the increased matric suction decreased significantly.
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Chen, Yen-Hsu, and 陳彥旭. "Assessment of Shear Strength of Vegetated Slopes and Measurement of Direct Shear Test on Sites." Thesis, 2013. http://ndltd.ncl.edu.tw/handle/04186999620063199482.
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碩士中國科技大學
土木與防災設計研究所
102
Combined direct shear measurement of the rooted soil can meet the needs of the field and laboratory. Therefore, the field direct shear measurement has multi-purpose properties. In the current study, the soil specimens were collected from fields. The direct shear tests were the proceeded and the relationship between the shear strength and the lateral displacement was determined simultaneously. After the test, the number of roots on the shear plane was counted and then the plant roots were extracted to make a direct tensile test. According to the data obtained from experiments, the statistical analysis was performed to obtain the parameters for the specific mechanics of the plant roots. Because the field plants exist in the poor-drained sandy and non-uniform grained soils, the roots of the plants on the field soils appear more complicated and differed in mean length with an acrylic box. Under the same parameters for the specific mechanics of the plant roots, the result was found to be different between the shear strength increment calculated by the root strength model and measured by the tests with various soil conditions.
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Lin, Yi-Pei, and 林宜霈. "A study of the shear strength of unsaturated silty clay using the multistage direct shear test." Thesis, 2017. http://ndltd.ncl.edu.tw/handle/03488004442505223897.
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碩士國立高雄第一科技大學
營建工程研究所
105
This study is application of the multistage direct shear test to reduce the cost and time associated with shear strength testing of unsaturated soils. In the saturated consolidated drainage direct shear test, in which net normal stress was set as 20kPa, 40kPa, 80kPa. The unsaturated consolidated drainage direct shear test, combined action of the net normal stress and the matric suction, the independent design panel used to control the matric suction. Six loading stages of matric suction, namely 25, 50, 100, 200, 250 and 300 kPa. The experimental results that under the control of single net normal stress and increasing matric suction, the change of water content of soil is influence of shear stress. The correlation coefficient (R2), at which the matric suction reaches the fourth loading stage is somewhat lower value, it can be relied upon in engineering practice.
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Lin, Yun-Wei, and 林昀葦. "THE Shear Strength Of Colluvium On Simple In-situ Test in Central Taiwan." Thesis, 2006. http://ndltd.ncl.edu.tw/handle/00079006033552517177.
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