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1
Vaid, Y. P., and S. Sasitharan. "The strength and dilatancy of sand." Canadian Geotechnical Journal 29, no. 3 (1992): 522–26. http://dx.doi.org/10.1139/t92-058.
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The effects of stress path and loading direction in the triaxial test on strength and dilatancy of sand are investigated. It is shown that the unique relationship observed between peak friction angle and dilation rate at peak in conventional triaxial tests is followed regardless of stress path, confining stress at failure, relative density, and the mode of loading (compression or extension). Key words : sand, peak friction angle, dilatancy, stress path, triaxial test.
2
Atkinson, J. H., and D. B. Clinton. "Stress Path Tests on 100 mm Diameter Samples." Geological Society, London, Engineering Geology Special Publications 2, no. 1 (1986): 133–37. http://dx.doi.org/10.1144/gsl.1986.002.01.28.
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AbstractThe use of stress path tests is discussed in relation to geotechnical design, and a description is given of the triaxial test stress path apparatus developed at The City University.Test results are presented from a series of triaxial tests following stress paths commonly encountered in engineering design problems. These are compared with the results of conventional triaxial tests.The stress-strain behaviour and pore pressure response of soil are shown to be very much dependent on the stress path followed, and the advantages of using stress-controlled loading in triaxial tests is demonstrated.
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Wang, Zhaofeng, Guangliang Feng, Xufeng Liu, and Yangyi Zhou. "An Experimental Investigation on the Foliation Strike-Angle Effect of Layered Hard Rock under Engineering Triaxial Stress Path." Materials 16, no. 17 (2023): 5987. http://dx.doi.org/10.3390/ma16175987.
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Deep underground engineering encounters substantial layered hard rock formations, and the engineering triaxial stress path involves an increase in maximum principal stress, constant intermediate principal stress, and a decrease in minimum principal stress. However, previous research has focused on rock layer angles under conventional triaxial stress conditions, disregarding the influence of foliation strike angles in engineering triaxial stress scenarios. This study experimentally investigates the effects of foliation strike angles on layered hard rock under an engineering triaxial stress path. To account for the brittleness of layered hard rock, we propose a specific small sample-processing method tailored to the foliation strike angle. True triaxial loading tests are conducted on steep, thin slate samples with two different loading orientations, accompanied by acoustic emission monitoring. Results indicate that the strength under a traditional true triaxial compression condition is similar for specimens with 90° and 0° strike angles. Stress–strain curves show that larger deformations occur perpendicular to bedding planes, while surface fractures propagate exclusively along the bedding planes. Mechanical responses differ significantly between specimens subjected to the engineering triaxial stress path at 0° and 90° strike angles compared to conventional true triaxial loading tests, with a lower bearing capacity and differentiated intermediate and minimum principal strains in the 0° case. Conversely, the 90° case exhibits a higher bearing capacity, consistent deformation, and more acoustic emission events. Numerical simulations comparing plastic zone sizes during actual underground excavation support these conclusions. These findings highlight the effects of foliation strike angles, favoring the 90° strike-angle configuration for excavation activities and providing enhanced stability in the surrounding rock mass.
4
Gautam, Rajeeb, and Ron CK Wong. "Transversely isotropic stiffness parameters and their measurement in Colorado shale." Canadian Geotechnical Journal 43, no. 12 (2006): 1290–305. http://dx.doi.org/10.1139/t06-083.
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Drained stress path triaxial tests and confined torsion tests were conducted on Colorado shale core samples to investigate transversely isotropic stiffness parameters at small strain deformation. Nonlinear plastic behaviour occurred along the primary loading path even at strains less than 0.01%. Nonlinear, hysteric behaviour was only observed during the loading–unloading path. However, the shale material displayed transverse isotropy in deformation, and very small or nondetectable Poisson's ratios in vertical and horizontal directions. This special response alludes to the postulate that the Colorado shale could be approximated by a transversely isotropic elasticity model at small strain levels with negligible yielding.Key words: anisotropy, elasticity, stiffness, triaxial test, torsion test, shale.
5
Xiao, Bin, Peijiao Zhou, and Shuchong Wu. "Creep Characteristics of Reconstituted Silty Clay under Different Pre-Loading Path Histories." Buildings 14, no. 5 (2024): 1445. http://dx.doi.org/10.3390/buildings14051445.
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Due to the long-term deformation settlement of foundations, issues such as damage and functional failure of buildings and structures have long been a concern in the engineering field. The creep of soil is one of the primary causes leading to long-term deformation of foundations. In this paper, the consolidation deformation, creep characteristics, and creep model of reconstituted saturated silty clay were studied using the isotropic consolidation creep test and triaxial compression creep test. The results show that for the isotropic consolidation creep test, although the applied load adopted different stages of loading, as long as the final applied confining pressure was the same, the number of stages applied by the confining pressure had little effect on the final isotropic consolidation deformation of the sample and the triaxial undrained shear strength after creep. However, for the triaxial shear creep test, it was found that under the same final deviatoric stress, the final deviatoric strain of the sample was closely related to the number of loading stages of deviatoric stress. The test showed that the more loading stages with the same deviatoric stress, the smaller the final deviatoric strain, and the triaxial undrained shear strength of the sample after creep increased. In addition, it was reasonable to set the pore pressure dissipation of the sample at 95% ((u0 − u)/u0 = 95%) as the time (t100) at which the primary consolidation of the soil sample was completed. The isotropic consolidation creep curves and the triaxial compression creep curves showed certain non-linearity. Then, the logarithmic model and the hyperbolic model were used to fit the creep curves of the samples. It was found that the hyperbolic model had a better fitting effect than the logarithmic model, but for the triaxial compression creep test, the creep parameters of the sample changed greatly. Therefore, studying the creep characteristics of soil under different pre-loading steps is of significant engineering importance for evaluating the long-term deformation of underground structures.
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Chen, Rui, and B. Stimpson. "Triaxial stress relaxation tests on Saskatchewan potash." Canadian Geotechnical Journal 32, no. 1 (1995): 11–21. http://dx.doi.org/10.1139/t95-002.
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Relative to the study of creep, the stress relaxation phenomenon has been overlooked in research on salt rocks, especially with respect to the behavior of salt in deep underground mining environments. In the laboratory tests described in this paper, deformational properties of potash were first studied by performing reverse-loading tests that approximately simulate in situ loading paths during excavation of underground cavities. Potash relaxation properties were then investigated by multiple-stage, repeated relaxation tests along the reverse-loading path. Results show that potash behavior along a reverse-loading path is highly stress rate dependent and is reflected in the dependence of the initial axial deformation modulus, ductile point, and post-yield behavior on the rate at which the deviatoric stress is applied to the specimen. The inserted relaxation phases did not significantly affect the subsequent behavior of the potash, and therefore inserted relaxation tests are useful for investigating time-dependent behavior at various stages of deformation. A linear relationship exists between normalized stress drop and logarithm of time, which might imply that potash has no creep limit. Finally, an attempt was made to extend a uniaxial strain hardening constitutive law postulated by another researcher to include confining pressure, and the experimental data were found to approximately fit the proposed constitutive model. Key words : potash, stress relaxation, triaxial tests, constitutive model.
7
Zhang, Shu Chao, Shao Hui He, Pei Wang, and Lin Li. "Axial Unloading Test of Soil Based on the GDS Triaxial Apparatus." Applied Mechanics and Materials 638-640 (September 2014): 407–11. http://dx.doi.org/10.4028/www.scientific.net/amm.638-640.407.
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Normal triaxial apparatus is suited to the loading stress path test, some stress path triaxial apparatus can be used to unload radial load smaller than the axial load, but it is difficult to unload axial load smaller than the radial load or even unload the axial load to zero. Using the iso-diameter headgear, different axial-radial unload ratio tests were done on the GDS triaxial apparatus, and the axial load was unloaded smaller than the radial load. During the test, it was found there are some deficiencies in the GDSLAB system. The results conformed to the characteristics of unloading test, which well verified the correctness of the test method and test results.
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Kim, In Tai, and Erol Tutumluer. "Unbound Aggregate Rutting Models for Stress Rotations and Effects of Moving Wheel Loads." Transportation Research Record: Journal of the Transportation Research Board 1913, no. 1 (2005): 41–49. http://dx.doi.org/10.1177/0361198105191300105.
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The latest research findings on stress rotations caused by moving wheel loads and their effects on permanent deformation or rut accumulation in pavement granular layers are presented. Realistic pavement stresses induced by moving wheel loads were examined in the unbound aggregate base and subbase layers, and the significant effects of rotation of principal stress axes were indicated for a proper characterization of the permanent deformation behavior. To account for the rutting performances of especially thick granular layers, a comprehensive set of repeated load triaxial tests was conducted in the laboratory. Triaxial test data were obtained and analyzed from testing aggregates under various realistic in situ stress paths caused by moving wheel loading. Permanent deformation characterization models were then developed on the basis of the experimental test data to include the static and dynamic stress states and the slope of stress path loading. The models that also considered the stress path slope variations predicted the stress path dependency of permanent deformation accumulation best. In addition, multiple stress path tests conducted to simulate the extension–compression–extension type of rotating stress states under a wheel pass gave much higher permanent strains than those of the compression-only single path tests. The findings indicated actual traffic loading simulated by the multiple path tests could cause greater permanent deformations or rutting damage, especially in the loose base or subbase, when compared with deformations measured from a dynamic plate loading or a constant confining pressure type laboratory test.
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Newson, T. A., M. C. R. Davies, and A. R. A. Bondok. "Selecting the rate of loading for drained stress path triaxial tests." Géotechnique 47, no. 5 (1997): 1063–67. http://dx.doi.org/10.1680/geot.1997.47.5.1063.
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Wang, Xiaoliang, Zhen Zhang, and Jiachun Li. "Triaxial behavior of granular material under complex loading path by a new numerical true triaxial engine." Advanced Powder Technology 30, no. 4 (2019): 700–706. http://dx.doi.org/10.1016/j.apt.2018.12.020.
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Zhang, Yingjie, Jiangteng Li, Gang Ma, and Shuangfei Liu. "Unloading Mechanics and Energy Characteristics of Sandstone under Different Intermediate Principal Stress Conditions." Advances in Civil Engineering 2021 (April 22, 2021): 1–9. http://dx.doi.org/10.1155/2021/5577321.
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The TRW-3000 true triaxial rock testing machine was used to conduct loading and unloading tests of sandstone under different σ 2 , and the true triaxial lateral unloading mechanics and energy characteristics of sandstone under different σ 2 were studied. The experimental results show the following: (1) compared with the results of the loading test, the peak strength of the sandstone under the unloading σ 3 path is reduced, the unloading direction has obvious expansion and deformation, and the amount of expansion increases significantly with the increase of σ 2 ; sudden brittle failure occurs at the end of unloading. E gradually decreases with the increase of H, and it performs well to use the cubic polynomial to fit the curve of E-H. (2) The Mogi–Coulomb strength criterion can accurately describe the true triaxial strength characteristics of sandstone under loading and unloading conditions. Compared with the results of the loading test, the values of c and φ obtained based on this criterion under the unloading σ 3 path are reduced. (3) Under the condition of unloading σ 3 , U, U e , and U d , when the specimen is broken, are all linearly positively correlated with σ 2 . U d increases nonlinearly with the increase of H, and as σ 2 increases, the slope of the U d -H curve becomes larger, and the specimen consumes more energy under the same unloading amount. Most of the energy absorbed by the specimen under the unloading σ 3 path is converted into U e , but as σ 2 increases, U d / U increases, and the energy consumed when the specimen is broken is greater.
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Sławińska-Budzich, Justyna, and Jacek Mierczyński. "Deformations and stability of granular soils: Classical triaxial tests and numerical results from an incremental model." Studia Geotechnica et Mechanica 42, no. 2 (2020): 137–50. http://dx.doi.org/10.2478/sgem-2019-0039.
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AbstractThis article presents a modified incremental model describing pre-failure deformations of granular soils under classical triaxial conditions. The original shape of equations has been proposed by Sawicki and Świdziński [40, 41]. A new form of equations that are consistent with the proposed definitions of deviatoric loading and unloading is suggested. Triaxial tests necessary for calibrating the proposed model have been performed. The modified model is used to simulate the deformations and stability of sand for every pre-failure loading path and makes it possible to describe the behaviour of granular soil under both drained and undrained conditions.A comparison of experimental and numerical results is presented. All investigations were performed in a classical tri-axial apparatus.
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Vaid, Y. P., E. K. F. Chung, and R. H. Kuerbis. "Stress path and steady state." Canadian Geotechnical Journal 27, no. 1 (1990): 1–7. http://dx.doi.org/10.1139/t90-001.
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The effect of stress path on the steady state line of a liquefiable sand is investigated. Results from undrained triaxial compression and extension tests on water-deposited sands show that the steady state line of a given sand, though unique in the effective stress space, is not so in the void ratio – effective stress space. The sand is contractive over a much larger range of void ratios in extension than in compression. While a single steady state line emerges for compression loading, extension loading yields several lines, each characteristic to a given deposition void ratio. All these extension lines lie to the left of the compression line in void ratio – effective stress space. Thus at a given void ratio, steady state strength is smaller in extension than in compression, the difference increasing as the sand becomes looser. The implications of the results are discussed in relation to practical design. Key words: sand, liquefaction, steady state, stress path.
14
Bergado, D. T., K. C. Chong, P. A. M. Daria, and M. C. Alfaro. "Deformability and consolidation characteristics of soft Bangkok clay using screw plate tests." Canadian Geotechnical Journal 27, no. 5 (1990): 531–45. http://dx.doi.org/10.1139/t90-069.
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This study centred on the performance of the screw plate test (SPLT) to determine the deformability and consolidation characteristics of soft Bangkok clay. For comparison, a series of stress-path-controlled triaxial consolidation tests (tri) were carried out on good quality samples of Bangkok clay taken from the same testing sites and imposed with the same loading conditions as the screw plate tests. Undrained and drained moduli and coefficients of consolidation were obtained from the stress-path-controlled triaxial consolidation tests and were compared with the corresponding values of the screw plate test. In addition, the ultimate bearing capacity was derived from the pressure–deformation relationships of the screw plate test results. A graphical method was used to compute the coefficient of consolidation from the screw plate tests and from stress-path-controlled triaxial consolidation test results. The compressibility data were also obtained from conventional oedometer tests (oed). Both cv (SPLT)/cv (tri) and cv (SPLT)/cv(oed) ratios compared favorably with the cv (field)/cv (laboratory) ratio obtained from past investigations. The data from pressure–settlement–time relationships of the screw plate tests were used to successfully predict values that compared favorably with the measured values at each stress level. The pressure–deformation–time relationship from stress-path-controlled triaxial consolidation tests were also evaluated, and they indicated behaviour similar to that of the screw plate test results. Soil parameters obtained from screw plate tests were subsequently used to predict the settlement of two test embankments, giving fairly close agreement with the observed values. Key words: soft clay, settlement, deformation, consolidation, screw plate test, triaxial test, embankment, prediction, stress path.
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Windisch, Andor. "Multiaxial Strength and Deformations of Concrete, Failure Modes and a New Failure Criterion." Concrete Structures 24 (2023): 137–48. http://dx.doi.org/10.32970/cs.2023.1.19.
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The multiaxial strength of concrete, the associated stress-strain relationships, the failure modes and the failure criteria are again and again in the interest of researchers. After a historical review the most important bi- and triaxial experiments loading through brushes are analyzed. Based on the principal strengths and the loading path-concept a new, transparent type of presentation of the ultimate strength surface (USS) is introduced. For concrete classes ≤ C100 simplified relative strength-increase values are proposed. The difficulties of deformation measurements are reviewed. The outlines of future bi- and triaxial tests are discussed. Two failure modes are appointed. Stress failure criterion of biaxial state of stress are presented. Instead of the Modified Mohr-Coulomb failure criterion Extended Rankine-type failure criteria are proposed. Further systematic tests are necessary to detect the rate of participation of the loading equipment.
16
Cao, Yangbing, Qiang Yan, Sui Zhang, and Fuming Cai. "Experimental Research on Anisotropy Characteristics of Shale under Triaxial Incremental Cyclic Loading and Unloading." Applied Sciences 14, no. 6 (2024): 2602. http://dx.doi.org/10.3390/app14062602.
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Shale is a common rock type that is associated with underground engineering projects, and several important factors, such as bedding structure, confining pressure, and the loading and unloading path, significantly influence the anisotropy of shale. Triaxial monotonic loading tests and triaxial incremental cyclic loading and unloading tests of shale under three kinds of confining pressures and five types of bedding inclination angles (θ) were thus performed to investigate the anisotropy of shale in terms of mechanical behavior, acoustic emission (AE), and energy evolution, and reveal the mechanism by which shale anisotropy is weakened. The results show that (1) the compressive strength and elastic modulus of shale decrease and then increase as the θ increases, and that both σ3 and incremental cyclic loading and unloading reduce the anisotropy in terms of the compressive strength and elastic modulus of shale, with the ratio of plastic strain to total strain reaching its maximum at a θ of 60° during each loading and unloading cycle. (2) The failure modes of shale with θ of 0°, 30°, and 90° under triaxial monotonic loading are similar to the counterparts under triaxial incremental cyclic loading and unloading, while the failure modes of shale with θ of 45° and 60° differ significantly under the two loading conditions, and interestingly, the degree to which the bedding plane participates in shale crack evolution under incremental cyclic loading and unloading is considerably lower than that under triaxial monotonic loading. (3) The cumulative AE count and AE b-value of shale first decrease and then increase as the θ increases, while the Felicity ratio decreases as the number of cycles increases. (4) As the θ increases, the total energy density U0 and the parameter m, which reflects the accumulation rate of elastic energy, first decrease and then increase, with both reaching a minimum at a θ of 60°. (5) The mode by which cyclic loading and unloading leads to failure in shale with a θ of 60° is similar to that at a θ of 0° and is the main mechanism by which shale anisotropy weakening occurs as a result of cyclic loading and unloading. The results provide experimental support and a theoretical basis for safer and more efficient underground engineering projects that involve shale.
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Vaid, Y. P., and S. Sivathayalan. "Static and cyclic liquefaction potential of Fraser Delta sand in simple shear and triaxial tests." Canadian Geotechnical Journal 33, no. 2 (1996): 281–89. http://dx.doi.org/10.1139/t96-007.
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The potential for static and cyclic liquefaction of the sand that underlies the highly seismic Fraser Delta is assessed under simple shear test conditions, typical of an earthquake shaking. A comparison of liquefaction potential is also made between simple shear and conventional triaxial stress conditions. It is shown that the liquefaction potential of sand is profoundly influenced by the stress path. The reduction factors currently applied to the cyclic triaxial resistance for representing simple shear response may involve a large degree of conservatism in design. A direct measurement of soil behaviour under stress conditions typical of earthquake loading may thus have large economic benefits. Key words: sand, liquefaction, static, cyclic, triaxial, simple shear.
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Mohammadi, Amirabbas, and David Airey. "Undrained response of Sydney sand under non-reversal cyclic loading." E3S Web of Conferences 92 (2019): 08005. http://dx.doi.org/10.1051/e3sconf/20199208005.
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Stress history and loading path can significantly influence the cyclic response of sands. It is well known that cyclic behaviour under non-symmetrical cycling is generally different from that under symmetrical loading around zero deviator stress. Anisotropic consolidation prior to cycling in triaxial apparatus changes the behaviour by exerting an initial static shear stress on critical planes. The present paper reports the results from a number of cyclic triaxial tests on anisotropically consolidated samples of Sydney beach sand. The samples are reconstituted in the laboratory and subjected to non-reversal cycling in compression only loading under undrained conditions. Typical test behaviours are described and the effects of cyclic stress ratio and initial state on the response are discussed. It is shown that the state parameter is capable of predicting the cyclic resistance and the trend of excess pore water pressure generation during one-way compressional cycling and, as has been well established for simple loading paths, critical state soil mechanics is able to provide a reliable framework to characterize the behaviour under different cyclic loading conditions.
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Maksimov, Fedor, and Alessandro Tombari. "Derivation of Cyclic Stiffness and Strength Degradation Curves of Sands through Discrete Element Modelling." Modelling 3, no. 4 (2022): 400–416. http://dx.doi.org/10.3390/modelling3040026.
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Cyclic degradation in fully saturated sands is a liquefaction phenomenon characterized by the progressive variation of the soil strength and stiffness that occurs when the soil is subjected to cyclic loading in undrained conditions. An evaluation of the relationships between the degradation of the soil properties and the number of loading cycles is essential for deriving advanced cyclic constitutive soil models. Generally, the calibration of cyclic damage models can be performed through controlled laboratory tests, such as cyclic triaxial testing. However, the undrained response of soils is dependent on several factors, such as the fabric, sample preparation, initial density, initial stress state, and stress path during loading; hence, a large number of tests would be required. On the other hand, the Discrete Element Method offers an interesting approach to simulating the complex behavior of an assembly of particles, which can be used to perform simulations of geotechnical laboratory testing. In this paper, numerical triaxial analyses of sands with different consistencies, loose and medium-dense states, were performed. First, static triaxial testing was performed to characterize the sand properties and validate the results with the literature data. Then, cyclic undrained triaxial testing was performed to investigate the impact of the number of cycles on the cyclic degradation of the soil stiffness and strength. Laws that can be used in damage soil models were derived.
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Corte, Marina Bellaver, Erdin Ibraim, Lucas Festugato, Andrea Diambra, and Nilo Cesar Consoli. "Stiffness of lightly cemented sand under multiaxial loading." E3S Web of Conferences 92 (2019): 11008. http://dx.doi.org/10.1051/e3sconf/20199211008.
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This paper presents experimental triaxial tests conducted on two lightly cemented sand samples on the set-up conditions of a Hollow Cylinder Torsional Apparatus (HCTA). The laboratory study has been carried out on an angular to sub-angular silica sand reinforced with Portland cement of high early strength. The samples have identical porosity/volumetric cement content ratio, η/Civ, values. The Young's modulus and shear modulus were measured by the application of a series of small unload-reload cycles at different investigation points along the triaxial stress path up to about 50% of the maximum deviatoric stress. At these investigation points, additional series of unload-reload cycles of higher amplitudes were also applied and the stiffness moduli assessed using local instrumentation. While the peak strength seems to be controlled by the density of the sand matrix, as extensive bond cementation damages occur at peak and pre-peak stages, the Young's modulus and shear modulus normalised by the void ratio function show the effect of the cementation ratio with higher values for the sample with higher cementation ratio.
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Sawicki, Andrzej, Justyna Sławińska, and Jacek Mierczyński. "Structure and Calibration of Constitutive Equations for Granular Soils." Studia Geotechnica et Mechanica 36, no. 4 (2015): 35–46. http://dx.doi.org/10.2478/sgem-2014-0034.
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Abstract The form of incremental constitutive equations for granular soils is discussed for the triaxial configuration. The classical elasto-plastic approach and the semi-empirical model are discussed on the basis of constitutive relations determined directly from experimental data. First, the general structure of elasto-plastic constitutive equations is presented. Then, the structure of semiempirical constitutive equations is described, and a method of calibrating the model is presented. This calibration method is based on a single experiment, performed in the triaxial apparatus, which also involves a partial verification of the model, on an atypical stress path. The model is shown to give reasonable predictions. An important feature of the semi-empirical incremental model is the definition of loading and unloading, which is different from that assumed in elasto-plasticity. This definition distinguishes between spherical and deviatoric loading/unloading. The definition of deviatoric loading/unloading has been subject to some criticism. It was therefore discussed and clarified in this paper on the basis of the experiment presented.
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Sivakumar, V., D. McKelvey, J. Graham, and D. Hughes. "Triaxial tests on model sand columns in clay." Canadian Geotechnical Journal 41, no. 2 (2004): 299–312. http://dx.doi.org/10.1139/t03-097.
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Vibro-stone columns can improve the bearing capacity and reduce the settlement of foundations. Their performance depends on the strength of the column material, reinforcement method of column installation, type of in situ soil, area replacement ratio, and column length. This paper examines the behaviour of small laboratory specimens of soft clay (undrained shear strength ≈ 30 kPa) reinforced with sand columns when tested under known boundary stress conditions. Two series of tests were carried out on kaolin specimens (diameter 100 mm, height 200 mm) in a triaxial cell. In the first series, specimens were reinforced with a 32 mm diameter column of sand, 80, 120, 160, or 200 mm long. Columns were installed by (i) compacting moist sand into a prebored hole or (ii) freezing a column of moist sand before inserting it into a prebored hole. In the second series, columns were reinforced with geo-grids before installation. The specimens were subjected to (i) uniform loading in which the load was applied over the entire surface area of the specimen or (ii) foundation-type loading in which only a small area in the centre of the specimen was loaded. Under uniform loading, the specimens containing a full-depth column were significantly stronger than specimens without columns. Specimens with single, partially penetrating columns installed by wet compaction were weaker than specimens without columns. When frozen columns were installed, strengths increased progressively. Under foundation-type loading, bearing capacities increased with an increase in column length. Geo-grid reinforcement produced significant increases in load-carrying capacity.Key words: ground improvement, undrained shear strength, consolidation, stress path.
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Kowalska, M. "Simulation of Stress Paths Derived from FEM Analysis in Triaxial Tests." Archives of Civil Engineering 59, no. 1 (2013): 119–29. http://dx.doi.org/10.2478/ace-2013-0005.
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Abstract Reliable estimation of geotechnical parameters is often based on reconstruction of a complete loading process of subsoil on a specimen in laboratory tests. Unfortunately laboratory equipment available in many laboratories is sometimes limited to just a triaxial apparatus - the use of which generates difficulties whenever a non-axisymmetric problem is analysed.The author suggests two simple operations that may be done to improve the quality of simulation in triaxial tests. The first one is based on the use of triaxial extension along the segments of the stress path p’-q-θ for which the Lode’s angle values are positive. The second one consists in a modification of the equivalent stress value in such a way that the current stress level in the specimen complies with results of FEM analysis.
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Mohamad, Habib Musa, Adnan Zainorabidin, and Adriana Erica Amaludin. "Stress Path Behaviour and Friction Angle Transition Due to the Cyclic Loading Effects." Civil Engineering Journal 9, no. 4 (2023): 895–905. http://dx.doi.org/10.28991/cej-2023-09-04-010.
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In various aspects, peat soil is different from mineral soil. Peat is a biogenic deposit that emerged within the last 10,000 years, during the post-glacial (Holocene) era. Peat is a soft soil that is unable to support external loads without experiencing significant deformations. Tyre pressure from automobiles and/or aeroplane wheels on paved surfaces creates traffic load, which can manifest as static or dynamic types of loading. To resolve the problem with peat soils, a thorough understanding of the static and dynamic behaviour of peat is still required. Many people who live near regularly used highways feel traffic vibration, and it is important to comprehend the nature of this issue to make predictions about potential solutions to this problem. As such, this study aims to investigate the cohesion (c) and friction angle (φ) properties of peat soil after it has been subjected to cyclic stress. Monotonic triaxial tests are conducted to ascertain the initial shear strength characteristics of the soil. Cyclic triaxial tests are performed with half of their maximum deviator stress to simulate the behaviour of peat soil under various effective stresses and frequencies of loading that are applied with 100 number of cycles. After applying various numbers of cycles of dynamic loading, the post-cyclic monotonic shear strengths were subsequently evaluated. It has been noted that irregular behaviour tends to occur more frequently at higher frequencies, particularly between 2 and 3 Hz. With higher frequencies being applied, the reduction in cohesion and friction angle becomes more evident. Doi: 10.28991/CEJ-2023-09-04-010 Full Text: PDF
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Sasitharan, S., P. K. Robertson, D. C. Sego, and N. R. Morgenstern. "Collapse behavior of sand." Canadian Geotechnical Journal 30, no. 4 (1993): 569–77. http://dx.doi.org/10.1139/t93-049.
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Loose cohesionless materials can collapse during either static or dynamic loading, resulting in a rapid buildup of pore pressure and associated reduction in shear resistance. As the cohesionless material collapses, it rapidly looses resistance until the acting shear stress decreases to the available residual or steady-state strength. Specially designed stress-path testing has been performed on sand to investigate this collapse process. Results from this test program and previously published data show that a state boundary can be defined when a cohesionless material moves from peak to steady state along a constant void ratio stress path regardless of whether it is loaded drained or undrained. Further, it is demonstrated that the state boundary represents a surface in the effective mean normal stress–deviator stress–void ratio space. Hence, flow slides and liquefaction can be initiated when the stress path followed during either drained or undrained loading attempts to cross this state boundary surface. Key wordy : sand, collapse, liquefaction, stress path, state boundary, triaxial test.
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Zhang, Yan Gang, Kun Yong Zhang, Wang Lin Li, and Qiao Zhen Shi. "Unloading Triaxial Experimental Study on Stress Path of Excavated Soil Slope." Advanced Materials Research 243-249 (May 2011): 2797–801. http://dx.doi.org/10.4028/www.scientific.net/amr.243-249.2797.
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The current research was implemented to study the practical unloading stress path that the slope mass experienced during the excavation process, which is very important in the stress and strain numerical analysis. Series of unloading tests were carried out under different confining pressure. During the test process, the minor principal stress was kept decreasing, while the major principal stress was kept unchanged to simulate the stress path in some locations of the soil slope, such as at the top of the slope. The corresponding conventional triaxial compression tests were also carried out as comparison. It is shown that there are many differences between the unloading and loading tests. Through analyzing, the tests results could be applied in the development of unloading constitutive models of excavation soil mass. Also, such unloading tests data are valuable in calibration and verification of the current existing popularly used models.
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Wang, Yan Fang, Zhi Gang Zhou, and Zheng Yin Cai. "Studies about Creep Characteristic of Silty Clay on Triaxial Drained Creep Test." Applied Mechanics and Materials 580-583 (July 2014): 355–58. http://dx.doi.org/10.4028/www.scientific.net/amm.580-583.355.
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The creep characteristic of saturated silty clay was studied by triaxial drained creep test through two stress paths of axial loading and lateral lightening. According to test data, some conclusions were submitted. First, the axial creep laws between the two stress paths were consistent on the drainage conditions. Volume strains were much smaller than axial strains. Volume strains presented shear dilatancy along with lightening confining pressure. The silty clay creep coefficient was put forward and its variation law was summarized. The silt soil creep coefficient was closely related to the deviatoric stress level. The two had a linear relationship. The silt soil creep coefficientincreased with deviatoric stress level and had no matter with the confining pressureand loading path.
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Deli, Á., and B. Vásárhelyi. "Investigation of the fracture process with different loading path triaxial tests on saturated sandstone." Bulletin of Engineering Geology and the Environment 59, no. 3 (2000): 187–93. http://dx.doi.org/10.1007/s100640000068.
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Gennaro, V. De, J. Canou, J. C. Dupla, and N. Benahmed. "Influence of loading path on the undrained behaviour of a medium loose sand." Canadian Geotechnical Journal 41, no. 1 (2004): 166–80. http://dx.doi.org/10.1139/t03-082.
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The results of an experimental programme aimed at studying the undrained behaviour of Hostun sand are presented in this paper. Specific conditions concerning the initial relative density (medium loose arrangements) and the loading paths (compression and extension under monotonic and cyclic loadings) were considered in the test programme. Monotonic tests carried out in both drained and undrained conditions show a significant difference in behaviour between compression and extension. It is observed that, in undrained conditions, Hostun sand is weaker in extension than in compression. In compression, the material is stable (dilatant) and the phase-transformation state controls the mechanical behaviour. In extension, the experimental results show an unstable behaviour (contractant), with monotonic, liquefaction-induced instability in undrained conditions. The results of cyclic tests, carried out with one- and two-way stress reversals, show a good correlation with the results of monotonic tests. The loading path strongly influences the undrained mechanical behaviour of the sand, mainly by inducing liquefaction in extension. This situation suggests that differences in soil fabric, caused by the sample preparation technique (air pluviation), can influence the sand behaviour by inducing a significant contraction in extension. By further analysing the cyclic results, it is shown that, during unloading, the stress paths reflect the transverse isotropy (orthotropy) of the sand, with stiffer elastic characteristics in the vertical direction than in the horizontal direction.Key words: liquefaction, cyclic mobility, sands, triaxial test, anisotropy, loading path.
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Liu, Yiming, Xinchao Liao, Lihua Li, and Haijun Mao. "Discrete Element Modelling of the Mechanical Behavior of Sand–Rubber Mixtures under True Triaxial Tests." Materials 13, no. 24 (2020): 5716. http://dx.doi.org/10.3390/ma13245716.
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Sand–rubber mixtures (SRMs) consisting of stiff sand particles and soft rubber particles are typical binary mixture materials that possess a variety of complicated properties. The complexity of the properties of sand–rubber mixtures is increased when complex stress path is involved. This study investigates the mechanical behavior of sand–rubber mixtures under generalized loading conditions using the discrete element method. A series of numerical true triaxial shear tests were conducted on pure sand and sand–rubber mixtures. The effect of rubber content and loading path on both of the macroscopic and microscopic performances of sand–rubber mixtures was investigated, and the associated microscale mechanism was also discussed. Numerical simulations show that the relationship between the peak friction angle ϕp and the intermediate principal stress ratio b is influenced by the addition of rubber particles, and a suggested explanation of this phenomenon is that the rubber particles mainly affect the inherent stability of the strong network. Particle-scale observations, including the coordinate number, the proportion of strong contacts, and the fabric anisotropy, are also presented in this study. Microscopic results confirm the explanation above, and explore the force transmission characteristics of sand–rubber mixtures under generalized loading conditions. This research can provide a reference for the constitutive model development of sand–rubber mixtures.
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Ng, Robert M. C., and K. Y. Lo. "The measurements of soil parameters relevant to tunnelling in clays." Canadian Geotechnical Journal 22, no. 3 (1985): 375–91. http://dx.doi.org/10.1139/t85-049.
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A comprehensive laboratory program was carried out on specimens trimmed from 152 mm diameter piston samples of a soft silty clay and a varved clay at a tunnel site in Thunder Bay. Results of conventional triaxial tests as well as special tests for the determination of anisotropic elastic parameters, simple shear tests, and stress path tests are presented.Results indicate that the unloading moduli are about twice the loading moduli, the Poisson's ratios in unloading are about three times those in loading, but the independent shear modulus is relatively unaffected. While the modulus is sensitive to mode of consolidation, drainage, and direction of stress path, the stress states at failure of all the different types of tests fall close to a single envelope for compression and extension. The choice of soil parameters for the analysis of deformation in tunnelling in soft clays is discussed. Key words: clay, tunnelling, stress path, deformation modulus, shear modulus, anisotropic elastic parameters, failure envelope.
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Wang, Zhe, Jing Li, and Ren Jie Shang. "Experimental Study on Mechanical Behavior of Concrete Loading along Path (Constant Stress, Constant Strain, Increasing Strain)." Applied Mechanics and Materials 238 (November 2012): 91–95. http://dx.doi.org/10.4028/www.scientific.net/amm.238.91.
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Triaxial compressive experiments were performed with normal concrete by using the large triaxial test system. The loading process was divided into two stages: (1) Under the condition of keeping the three axial stresses equivalent, the compressive stress was increased to a specified value p, which was maintained for a period of time; (2) The strain in y direction was increased monotonously while the stress in x direction and the strain in z direction both remained constant. In this paper, the study on the experiments indicates: the minimum principal stress significantly influences the strength of concrete, i.e., the greater the minimum principal stress is, the greater the concrete strength is; the stress in y direction where the strain stayed constant is the middle principal stress; the constant strain influences the relationship between σ2 and σ1, they reach the peak values at the same time and approximate to linear relationships in much parts of their descending stage, curvature only appears at their ends; When ε13>8, each relationship curve of τ13-γ13 gradually becomes horizontal；Below a line AB in figure of coordinate system εx, εy the curves of εx-εy approximately parallel to each other; If the minimum principal stress is 15MPa or 20MPa, After εkk reaches the peak point, the volume gradually becomes stable after a transient decrease stage.
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Zhang, Liang, Fujun Niu, Minghao Liu, Jing Luo, and Xin Ju. "Mechanical Behavior of Cracked Rock in Cold Region Subjected to Step Cyclic Loading." Geofluids 2022 (January 17, 2022): 1–15. http://dx.doi.org/10.1155/2022/6220549.
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In order to analyze the mechanical behavior of cracked rock in cold region subjected to cyclic loading, step cyclic loading and unloading (SCLU) triaxial tests with different stress paths have been designed. The mechanical responses such as strength, deformation, and failure mode were analyzed. The test results show that limestone has obvious strengthening effect under cyclic loading due to local crushing and filling of internal structural plane. The strengthening effect and fatigue damage effect caused by cyclic loading and the impact damage effect caused by the upgraded of stress level have an effect on mechanical response of cracked rock, and the degree of influence is related to the stress path. Under the stress path of constant stress lower limit (CSLL), the strengthening effect of rock was more prominent and its strength was enhanced. It was mainly subjected to progressive fatigue damage and had a buffering effect in the failure process. However, under the stress path of increasing the stress lower limit (ISLL), the rock suffered significant impact damage and entered the fatigue damage stage in advance, which led to its strength reduction and sudden failure when entering the next stress level. In addition, during the loading process, larger initial stress amplitudes led to more obvious cyclic strengthening effects, while smaller initial stress amplitudes led to greater plastic deformation and energy dissipation, and the rock was more prone to progressive damage.
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Uthayakumar, M., and Y. P. Vaid. "Static liquefaction of sands under multiaxial loading." Canadian Geotechnical Journal 35, no. 2 (1998): 273–83. http://dx.doi.org/10.1139/t98-007.
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A fundamental study of the undrained behaviour of sands under multiaxial loading is presented. The investigation was carried out using Fraser River and Syncrude sands in a hollow cylinder torsional shear device. Shear loading was carried out under strain control to capture the postpeak strain-softening characteristics of loose sands. It is shown that the undrained response of loose sands is highly dependent on the loading direction. The friction angle mobilized at phase transformation and steady state is a unique material property, independent of the mode of loading, direction of principal stress and initial consolidation stress, and void ratio state. There is no unique relationship between steady state strength and void ratio which is independent of stress path and the level of initial confining stress.Key words: anisotropy, hollow cylinder torsional shear, liquefaction, sand, simple shear, triaxial.
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Zhang, Yang, Yongjie Yang, and Depeng Ma. "Mechanical Characteristics of Coal Samples under Triaxial Unloading Pressure with Different Test Paths." Shock and Vibration 2020 (August 10, 2020): 1–10. http://dx.doi.org/10.1155/2020/8870821.
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In order to understand the influence of unloading path on the mechanical properties of coal, triaxial unloading confining pressure tests with different initial confining pressure and different unloading rate were carried out. The test results show that the triaxial unloading strength of coal samples under different test conditions is lower than conventional triaxial tests, but the brittleness characteristics are more obvious. This result indicates that the coal samples are easily damaged under unloading conditions. In the axial loading stage of the confinement unloading tests, the axial strain plays a leading role. However, during the confining pressure unloading stage, the circumferential deformation is large, which is the main deformation in this stage. Higher unloading rates of confining pressure are associated with shorter times between the peak stress position and sample complete failure. This shows that samples are more easily destroyed under higher unloading rates and the samples are more difficultly destroyed under lower unloading rates. In addition, with increasing unloading rate, the peak principal stress difference and confining pressure at failure decrease gradually, whereas the confining pressure difference at failure increases gradually. Compared with conventional triaxial compression tests, the cohesion of coal is reduced and the internal friction angle is increased under the condition of triaxial unloading test.
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Chen, Zheng-Han, D. G. Fredlund, and Julian K.-M. Gan. "Overall volume change, water volume change, and yield associated with an unsaturated compacted loess." Canadian Geotechnical Journal 36, no. 2 (1999): 321–29. http://dx.doi.org/10.1139/t98-097.
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This paper presents the overall volume change, water volume change, and yield associated with an unsaturated, compacted, low-plasticity loess from China. Two types of tests were conducted using a modified triaxial apparatus, namely isotropic compression tests with controlled suction (ICT), and triaxial shrinkage tests (TST). In the triaxial shrinkage tests, the net cell pressure is controlled and suction is allowed to increase. The results show that the stress path has a significant effect on overall volume change and the water volume change. The soil parameters related to overall volume change and the water volume change for the isotropic compression tests vary significantly in the low suction range, whereas the same soil parameters related to the triaxial shrinkage tests exhibit gradual changes. The yield net mean stress for the loading-collapse yield curve increases with suction. The yield suction is not equal to the maximum suction experienced by the soil specimen for the suction increase yield locus. Based on the test data obtained from the low-plasticity loess, a modified criterion for yield associated with suction increase is proposed. The proposed modified yield criterion should be valid for loess and silts of similar densities and plasticities.
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Liu, Furong, Zhiwei Zhou, Wei Ma, Shujuan Zhang, and Zhizhong Sun. "Dynamic Parameters and Hysteresis Loop Characteristics of Frozen Silt Clay under Different Cyclic Stress Paths." Advances in Materials Science and Engineering 2021 (June 8, 2021): 1–22. http://dx.doi.org/10.1155/2021/3763181.
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In cold regions, the long-term stability of engineering facilities is unavoidably influenced by the negative temperature, freeze-thaw process, dry-wet process, and dynamic loading conditions induced by earthquakes and traffic loads. In order to investigate the effects of different cyclic stress paths on the evolution of dynamic mechanical properties of frozen silt clay, a series of cyclic triaxial tests with variation confining pressure (VCP) or constant confining pressure (CCP) were performed. Triaxial low-temperature apparatus (MTS-810) was taken advantage of to simulating various cyclic stress paths by changing cyclic loading conditions of axial stress and confining pressure. In this paper, the evolution features of the axial resilient modulus, damping ratios, and the shape of hysteresis loops with an increase in the number of load cycles under different dynamic stress paths are comprehensively studied. The results show that the loading angle of cyclic stress path and the phase difference between cyclic axial stress and confining pressure are the main factors that remarkably affect the development characteristics of the resilient modulus and damping ratio. With increasing of the loading angle and phase difference, the resilient modulus increases, but damping ratio increases with increasing of loading angle and with decreasing of phase difference. With the continuous increase in the number of loading cycles, the samples of frozen soil show compacting and hardening characteristics. With an increase in the number of load cycles, the shape of hysteresis loop becoming narrows, the resilient modulus decreases at the initial stage and then gradually increases, and the damping ratio stably decreases. According to contrastively analyzing the evolution of dynamic parameters and the shape features of hysteresis loops under various cyclic stress paths, it can be clearly discovered that the evolution of sample microstructure and the development of dynamic characteristics of frozen samples have obvious dependence on the cyclic stress path. Therefore, the effects of variable confining pressure (VCP) on dynamic behaviors of frozen soils are nonnegligible in practical cold region engineering.
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Zhao, Yanru, Tiande Wen, Xiaohui Sun, Liping Huang, and Rui Chen. "Effect of Loading Path on the Mechanical Properties of Completely Decomposed Granite Soil Based on the Multiscale Method." Advances in Civil Engineering 2021 (January 30, 2021): 1–12. http://dx.doi.org/10.1155/2021/6635768.
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Mechanical properties of intact completely decomposed granite (CDG) soil, widely distributed in South China, decrease drastically as encountering external load-related disturbance or soaked by water. In this study, staged triaxial consolidated drained (CD) test and microscopic scanning were conducted using intact CDG specimens extracted from a construction site to investigate the mechanical behavior and microscopic pore distribution. The results show that the stress-strain relationship reveals a shrinking behavior in the first-stage loading and a brittle behavior in the second-stage loading. The development of cracks is affected by the principal stress, which causes the pores and cracks to shrink or partially close. In addition, Esec-1 increases linearly with the increase of confining pressure, but Esec-2 decreases exponentially.
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Shu, Rongjun, Lingwei Kong, Bingheng Liu, and Juntao Wang. "Stress–Strain Strength Characteristics of Undisturbed Granite Residual Soil Considering Different Patterns of Variation of Mean Effective Stress." Applied Sciences 11, no. 4 (2021): 1874. http://dx.doi.org/10.3390/app11041874.
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Granite residual soil is one of the most frequently encountered problem soils in tropical regions, whose mechanical behavior heavily depends on the pattern of variation of mean effective stress (p’) during shearing, which can be classified into three categories: increasing-p’, constant-p’, and decreasing-p’. Unfortunately, so far, the stress–strain strength characteristics of granite residual soils have been studied mainly under increasing-p’ stress paths, although it is very likely to encounter stress paths with decreasing p’ in practice, especially in excavation engineering. Moreover, most pertinent research has focused on remolded granite residual soils, whereas undisturbed specimens have not yet received enough attention. In this paper, stress path triaxial tests considering different patterns of variation of mean effective stress were conducted on an undisturbed granite residual soil. Subsequently, a variable termed loading angle was introduced to quantitatively represent stress path. The influences of stress path on the Mohr–Coulomb strength parameters, deformation characteristics, ductility, and shearing stiffness were analyzed, with an emphasis on the role of pattern of variation of mean effective stress. The experimental results show that friction angle of the soil increases while cohesion decreases with the increase in loading angle. The increase in loading angle leads to less volume contraction and smaller failure strain. During shearing, the soil exhibited a less brittle response under stress paths with smaller loading angles. The initial secant shear modulus first decreased and then increased as the loading angle increased, with the minimum shearing stiffness occurring at a certain loading angle lying between 90° and 123.7°.
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Cai, Yuanqiang, Qi Sun, Lin Guo, C. Hsein Juang, and Jun Wang. "Permanent deformation characteristics of saturated sand under cyclic loading." Canadian Geotechnical Journal 52, no. 6 (2015): 795–807. http://dx.doi.org/10.1139/cgj-2014-0341.
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The loading path involving principal stress rotation (PSR) during shear is an important phenomenon encountered in many field conditions. Typically for traffic loading, both the magnitude and direction of principal stresses may vary with time due to the motion of vehicles, and the stress path can be mimicked by a heart shape in the deviatoric stress space. Conventional triaxial tests are not suitable to recreate this type of stress path in that no torsional shear stress can be applied on the test samples. To overcome this limitation, a series of tests using a hollow cylinder apparatus were conducted on sand to investigate the permanent deformation characteristics under drained conditions with different levels of confining pressure (σc), cyclic vertical stress ratio (CVSR), and cyclic torsional stress ratio (η). The results clearly show an increase in the permanent deformation with η, indicating that the PSR effect on permanent deformation cannot be ignored. Both σc and CVSR were found to also affect permanent deformation, which was more pronounced when PSR was coupled into the test. A five-parameter formulation that accounted for the effect of confining pressure, deviatoric stress, torsional shear stress, and number of loading cycles was subsequently established to analyze the permanent strain. The formulation coefficients were first determined and then used to explain the effects of stress variables on the permanent deformation. Validation studies were performed to address the adequacy of the formulation to predict permanent deformation.
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Theocaris, P. S. "Positive and Negative Failure-Shears in Orthotropic Materials." Journal of Reinforced Plastics and Composites 11, no. 1 (1992): 32–55. http://dx.doi.org/10.1177/073168449201100103.
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Failure predictions of off-axis loaded fiber composite laminae are given according to the elliptic paraboloid failure criterion for anisotropic solids [1]. The failure condition assumes that for any anisotropic solid a safe triaxial loading path exists, along the hydrostatic compression, and thus the failure surface must be open-ended. By appropriately formulating the failure criterion, it is shown that the geometric interpretation of the failure surface in the principal stress space is an elliptic paraboloid (EPFS) whose axis of symmetry is parallel to the hydrostatic axis in the principal stress space. Because of the shape and position of the EPFS, the intersections by principal stress planes corresponding to loadings of off-axis laminae of a fiber composite are represented by ellipses whose origins are displaced from the origin of the stress reference frame. This fact creates unequal shear yield stresses in the positive and negative sense clearly manifested in a pure shear failure loading. The predictions of the above criterion for plane stress failure loadings of laminae, and especially for pure shear induced failures, are compared with existing experimental data for various fiber composites and are shown to be in satisfactory agreement.
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Patutin, AV, and SV Serdyukov. "Laboratory stands for hydraulic fracturing simulation in a nonuniform stress field." IOP Conference Series: Earth and Environmental Science 991, no. 1 (2022): 012035. http://dx.doi.org/10.1088/1755-1315/991/1/012035.
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Abstract The paper considers the capabilities of well-known laboratory facilities for hydraulic fracturing modeling under the true triaxial loading conditions. Of greatest interest are the stands that allow you to create a crack in large cubic samples with an edge length of 200 mm or more. In this case, it is possible to reduce the influence of edge effects from the boundaries of the sample on the propagation path of the discontinuity. The review includes research results obtained using 10 different facilities located in major scientific centers.
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Castelli, Francesco, Antonio Cavallaro, Salvatore Grasso, and Valentina Lentini. "Undrained Cyclic Laboratory Behavior of Sandy Soils." Geosciences 9, no. 12 (2019): 512. http://dx.doi.org/10.3390/geosciences9120512.
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The complex cyclic shear stress path experienced by the soil during an earthquake, which could also induce liquefaction phenomena, can be approximated in the laboratory only by using sophisticated testing apparatuses. Cyclic triaxial tests have been widely used, especially for coarse grained soils, as in this study. In the framework of the design for the seismic retrofitting of the ‘‘Ritiro viaduct’’ foundations along the A20 motorway connecting Messina with Palermo (Italy), a soil liquefaction study was also carried out. With this aim, a detailed geological and geotechnical characterization of the area was performed by in situ and laboratory tests, including seismic dilatometer Marchetti tests (SDMTs), the combined resonant column (RCT) and cyclic loading torsional shear tests (CLTSTs), and undrained cyclic loading triaxial tests (CLTxTs). In particular, the paper presents the results of cyclic triaxial tests carried out on isotropically consolidated specimens of a sandy soil. The seismic retrofitting works include the reinforcement of the foundation and replacement of the decks with newly designed type and structural schemes, mixed steel, and concrete with continuous girder. During the investigation, data were acquired for the characterization of materials, for the definition of degradation phenomena with the relative identification of possible causes, and for the estimation of the residual performance characteristics of the building. The structural campaign of investigations necessary to determine all of the key parameters useful for a correct definition of the residual performance capabilities of the work was divided into two phases: One in situ and one in the laboratory.
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BUTKOVICH, JEREMY N., and YOUSSEF M. A. HASHASH. "Neural network material model enhancement: Optimization through selective data removal." Artificial Intelligence for Engineering Design, Analysis and Manufacturing 21, no. 1 (2007): 61–72. http://dx.doi.org/10.1017/s089006040707014x.
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Neural network (NN)-based constitutive models have been used increasingly to capture soil constitutive response. When combined with the self-learning simulation (SelfSim) inverse analysis framework, NN models can be used to extract soil behavior when given field measurements of boundary deformations and loads. However, the data sets used to train and repeatedly retrain the NN models are large, and training times, especially when used in SelfSim, are long. A diverse set of stress–strain data is extracted from a simulated braced excavation problem to train a NN-based constitutive model. Several methods for reducing the data set size are proposed and evaluated. Each of these methods selectively removes training data so that the smallest amount of data is used to train the NN. The Gaussian point method removes data based on its position in each finite element in the model. The lattice method removes data so that all remaining points are evenly spaced in stress space. Finally, the loading path method compares the stress–strain history of each Gaussian point and removes points with similar loading histories. Each of these methods shows that a large amount of the training data (up to 94%) can be removed without adversely affecting the performance of the NN model, with the loading path method showing the best and most consistent performance. Model training times are reduced by a factor of 20. The performance of the loading path method is also demonstrated using stress–strain data extracted from a simulated laboratory triaxial compression test with frictional ends.
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Gabet, Thomas, Yann Malécot, and Laurent Daudeville. "Triaxial behaviour of concrete under high stresses: Influence of the loading path on compaction and limit states." Cement and Concrete Research 38, no. 3 (2008): 403–12. http://dx.doi.org/10.1016/j.cemconres.2007.09.029.
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Ma, Xiaodong, John W. Rudnicki, and Bezalel C. Haimson. "Failure characteristics of two porous sandstones subjected to true triaxial stresses: Applied through a novel loading path." Journal of Geophysical Research: Solid Earth 122, no. 4 (2017): 2525–40. http://dx.doi.org/10.1002/2016jb013637.
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Sun, Qi, Yuanqiang Cai, Jian Chu, Quanyang Dong, and Jun Wang. "Effect of variable confining pressure on cyclic behaviour of granular soil under triaxial tests." Canadian Geotechnical Journal 54, no. 6 (2017): 768–77. http://dx.doi.org/10.1139/cgj-2016-0439.
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Previous studies were performed to use combined cyclic deviatoric stress and confining pressure to simulate cyclic vertical and horizontal normal stresses under traffic loading. The effect of variable confining pressure (VCP) on the permanent deformation of soils was investigated. However, some studies concluded VCP could promote the development of permanent deformation compared to the tests with constant confining pressure (CCP), while others drew the opposite conclusions. In this study, three types of CCP and VCP tests with identical maximum stress, identical average stress, and identical initial stress were conducted. Test results showed VCP tests accumulated more permanent strains when CCP and VCP tests had identical maximum or average stress, and the permanent strains increased with the decrease in the inclinations of stress paths, while similar permanent strains were generated when CCP and VCP tests had identical initial stress. In addition, larger permanent strains were generated with the increase in stress ratio or length of stress path in both CCP and VCP tests. Considering that different strains were cumulated in CCP and VCP tests with the same stress ratio, it is recommended that both stress ratio and length of stress path be considered to assess the permanent deformation.
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Skopek, Peter, N. R. Morgenstern, P. K. Robertson, and D. C. Sego. "Collapse of dry sand." Canadian Geotechnical Journal 31, no. 6 (1994): 1008–14. http://dx.doi.org/10.1139/t94-115.
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Loose cohesionless saturated materials have proved responsible for a number of serious or catastrophic flow slides. Liquefaction failures with no obvious triggering mechanism have also been recorded. This phenomenon of sudden liquefaction without a presence of cyclic shear stresses is often referred to as spontaneous or static liquefaction. Results from previously published studies suggest that liquefaction is triggered not by the undrained loading and generation of pore pressures but by the collapse of the metastàble sand structure, which in turn generates the driving pore pressures in a saturated material. Hence, the collapse is a characteristic response of a material to certain stress states rather than a result of some enforced undrained loading. This theory is evaluated on very loose dry Ottawa sand. It is shown that the very loose dry sand when subjected to a constant deviatoric stress path significantly changes its behavior at a certain discreet stress state, increases compressibility, and becomes increasingly unstable. This results in collapse – vigorous contraction of the specimen. This structural collapse appears to be equivalent to the pore-pressure generation in collapsing, very loose saturated sand. Key words : dry sand, collapse, liquefaction, stress path, triaxial cell.
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Wang, Yin, Zhen Qi, Tongzhong Wei, Junji Bao, Xun Zhang, and Yansheng Zhou. "Numerical Study on the Responses of Suction Pile Foundations under Horizontal Cyclic Loading Considering the Soil Stiffness Degradation." Journal of Marine Science and Engineering 11, no. 12 (2023): 2336. http://dx.doi.org/10.3390/jmse11122336.
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This paper analyzes the deformation responses of single-cylinder and four-cylinder suction pile foundations in soft clay under horizontal cyclic loading. Based on the existing stiffness degradation model of soft clay, a more suitable model for marine soft clay is proposed by carrying out dynamic triaxial experiments under different stress levels. The stiffness degradation and cumulative displacement of soil under cyclic loading are implemented in ABAQUS by compiling a USDFLD subroutine. The rationality is verified by comparison with the displacement response of the pile measured by the centrifugal model test and the scaled model test reported in the literature. With the aid of the current model, the stress state and deformation of suction pile foundations under horizontal cyclic load are further analyzed. The numerical results reveal the path of soil stiffness degradation and the deformation response of foundations during horizontal cycling. The cumulative displacement generated by the cyclic load is quantitatively displayed. It is proved that this model has the capability to reflect the cumulative displacement under cyclic loading and shows promise in analyzing the long-term deformation response of offshore foundations.
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Feng, Wang, Chi Shichun, Li Shijie, and Jia Yufeng. "Testing and Micromechanical Modelling of Rockfill Materials Considering the Effect of Stress Path." Mathematical Problems in Engineering 2016 (2016): 1–14. http://dx.doi.org/10.1155/2016/7630541.
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We have extended the micromechanics-based analytical (M-A) model to make it capable of simulating Nuozhadu rockfill material (NRFM) under different stress paths. Two types of drained triaxial tests on NRFM were conducted, namely, the stress paths of constant stress ratio (CSR) and the complex stress paths with transitional features. The model was improved by considering the interparticle parameter variation with the unloading-reloading cycles and the effect of the stress transition path. The evolution of local dilatancy at interparticle planes due to an externally applied load is also discussed. Compared with Duncan-Chang’s E-u and E-B models, the improved model could not only better describe the deformation properties of NRFM under the stress path loading, but also present the volumetric strain changing from dilatancy to contractancy with increasing transitional confining pressures. All simulations have demonstrated that the proposed M-A model is capable of modelling the mechanical behaviour of NRFM in the dam.