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Journal articles on the topic 'Suction-Oedometer'

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Published: 4 June 2021
Last updated: 1 February 2022

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1

Rezania, Mohammad, Meghdad Bagheri, and Mohaddeseh Mousavi Nezhad. "Creep and consolidation of a stiff clay under saturated and unsaturated conditions." Canadian Geotechnical Journal 57, no. 5 (May 2020): 728–41. http://dx.doi.org/10.1139/cgj-2018-0398.

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In this paper, the one-dimensional (1D) time-dependent behaviour of natural and reconstituted London Clay samples under saturated and unsaturated conditions is studied. For this purpose, a set of 1D consolidation tests including multi-staged loading (MSL) oedometer tests and single-staged loading (SSL) long-term oedometer creep tests were carried out on saturated and unsaturated specimens. Conventional oedometer cells were used for tests on saturated specimens, whereas a newly designed unsaturated oedometer cell, equipped with two high-capacity tensiometers (HCTs) for suction measurements, was used for unsaturated tests. The tests results revealed stress dependency and suction dependency of primary and secondary consolidation responses of the soil samples. Furthermore, counter to formerly acknowledged suggestions of independency of the slope of normal consolidation line to suction changes, it was observed that an increase in suction results in a decrease of the slope of compression curve (Cc) and the creep index (Cαe) values and an increase in yield vertical net stress (σp). Moreover, the Cαe/Cc ratio for London Clay was found to be stress- and suction-dependent, unlike the previously suggested hypotheses.
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2

Rao, Sudhakar M., and P. Shivananda. "Role of osmotic suction in swelling of salt-amended clays." Canadian Geotechnical Journal 42, no. 1 (February 1, 2005): 307–15. http://dx.doi.org/10.1139/t04-086.

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The present study examines the influence of extraneous salt addition on pore-fluid osmotic suction of a clay soil. The dependence of swell potentials of the salt-amended clay specimens on initial pore-fluid osmotic suction is also examined. The osmotic suctions predicted by Van't Hoff's equation are in excess or smaller than the values calculated from the pore water electrical conductivity, depending on whether the Van't Hoff factor in the Van't Hoff equation is included or not. Experimental results suggest that the salt-amended specimens absorbed water and swelled in response to matric suction and chemical concentration gradients on inundation with water in oedometer cells. Salt also diffused from the soil pores of salt-amended specimens to the reservoir water in oedometer cells in response to chemical concentration gradients. Reduction in effective stress from osmotic flow into the soil specimen and increase in interparticle repulsion from reduction in pore-water salt concentration rendered the total swell potentials of salt-amended specimens independent of initial pore-fluid osmotic suction. The initial pre-fluid osmotic suction does, however, significantly affect the rate of swelling.Key words: clays, chemical properties, swell potential, suction.
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3

Fattah, Mohammed Y., and Basma A. Dawood. "Time-dependent collapse potential of unsaturated collapsible gypseous soils." World Journal of Engineering 17, no. 2 (March 2, 2020): 283–94. http://dx.doi.org/10.1108/wje-09-2019-0276.

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Purpose This study aims to predict the volume changes and collapse potential (CP) associated with the changes in soil suction by using the pressure cell and the effect of initial load on soil suction. Three types of gypseous soils have been experimented in this study, sandy gypseous soil from different parts of Iraq. A series of collapse tests were carried out using the oedometer device [single oedometer test (SOT) and double oedometer test (DOT)]. In addition, large-scale model with soil dimensions 700 × 700 × 600 mm was used to show the effect of water content changes in different relations (collapse with time, stress with time, suction with time, etc.). Design/methodology/approach A series of collapse tests were carried out using the oedometer device (SOT and DOT). In addition, a large-scale model with soil dimensions 700 × 700 × 600 mm was used to show the effect of water content changes in different relations (collapse with time, stress with time, suction with time, etc.). Findings The CP increases with the increasing of the void ratio for each soil. For each soil, the CP decreased when the initial degree of saturation increased. Kerbala soil with gypsum content (30%) revealed collapse value higher than Tikrit soil with gypsum content (55%) under the same initial conditions of water content and density, this is because the higher the Cu value of Kerbala soil is, the more well-graded the soil will be. Upon wetting, the smaller particles or fractions of the well-graded soil tend to fill in the existing voids, resulting in a lower void ratio as compared to the poorly graded one. Consequently, soils with high Cu value tend to collapse more than poorly graded ones. The compressibility of the soil is low when loaded under unsaturated condition, the CP for samples tested in the DOTs under stress level 800 kPa are greater than those obtained from collapse test at a stress level of 200 kPa. Originality/value The initial value of suction for all soils increases with initial water content decreases.
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4

Tu, Hongyu, and Sai K. Vanapalli. "Prediction of the variation of swelling pressure and one-dimensional heave of expansive soils with respect to suction using the soil-water retention curve as a tool." Canadian Geotechnical Journal 53, no. 8 (August 2016): 1213–34. http://dx.doi.org/10.1139/cgj-2015-0222.

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The one-dimensional (1-D) potential heave (or swell strain) of expansive soil is conventionally estimated using the swelling pressure and swelling index values that are determined from different types of oedometer test results. The swelling pressure of expansive soils is typically measured at saturated condition from oedometer tests. The experimental procedures of oedometer tests are cumbersome as well as time-consuming for use in conventional geotechnical engineering practice and are not capable of estimating heave under different stages of unsaturated conditions. To alleviate these limitations, semi-empirical models are proposed to predict the variation of swelling pressure of both compacted and natural expansive soils with respect to soil suction using the soil-water retention curve (SWRC) as a tool. An empirical relationship is also suggested for estimating the swelling index from plasticity index values, alleviating the need for conducting oedometer tests. The predicted swelling pressure and estimated swelling index are then used to estimate the variation of 1-D heave with respect to suction for expansive soils by modifying Fredlund’s 1983 equation. The proposed approach is validated for eight field sites from six countries — namely, Saudi Arabia, Australia, Canada, China, USA, and UK — and on six different compacted expansive soils from USA.
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5

Villar, M. V., and P. L. Martin. "Suction-controlled oedometer tests in montmorillonite clay: preliminary results." Geological Society, London, Engineering Geology Special Publications 11, no. 1 (1996): 309–12. http://dx.doi.org/10.1144/gsl.eng.1996.011.01.41.

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6

Derfouf, Feth-Ellah Mounir, Nabil Abou-Bekr, Said Taibi, Mohammed Amine Allal, and Assia Benchouk. "Hydromechanical behaviour of a marl on controlled suction oedometer path." European Journal of Environmental and Civil Engineering 24, no. 4 (November 10, 2017): 500–519. http://dx.doi.org/10.1080/19648189.2017.1399293.

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7

Rampino, C., C. Mancuso, and F. Vinale. "Laboratory testing on an unsaturated soil: equipment, procedures, and first experimental results." Canadian Geotechnical Journal 36, no. 1 (August 8, 1999): 1–12. http://dx.doi.org/10.1139/t98-093.

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This paper describes two new apparatuses recently developed at the Università di Napoli Federico II (Italy) in order to test soils under unsaturated conditions. The related experimental procedures and the first results obtained on a dynamically compacted silty sand are also discussed. The devices mentioned are a Bishop and Wesley stress-path cell and a Wissa oedometer, modified to control matric suction and to measure all the stress-strain variables relevant to unsaturated soil mechanics. Specific experimental procedures were established to perform tests under general conditions and were carefully verified during several tests. Using the triaxial cell, isotropic and anisotropic compression stages were carried out under constant suction levels of 0, 100, 200, and 300 kPa. Furthermore, two deviator stages were performed following different stress paths and water drainage conditions. Using the oedometer, an additional suction level (400 kPa) was investigated during compression tests driven up to 5 MPa of vertical net stress (sigmav - ua). This research is a part of a major project in progress at the Dipartimento di Ingegneria Geotecnica of Naples; it is aimed at the experimental analysis of the behaviour of several dynamically compacted soils and at the numerical modelling of boundary problems related to earth structures.Key words: unsaturated soils, equipment layout, silty sand, matric suction.
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8

Rampino, Celestino, Claudio Mancuso, and Filippo Vinale. "Experimental behaviour and modelling of an unsaturated compacted soil." Canadian Geotechnical Journal 37, no. 4 (August 1, 2000): 748–63. http://dx.doi.org/10.1139/t00-004.

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This paper reports the experimental study and modelling of the mechanical response of a silty sand used in the core of the Metramo dam, Italy. Specimens were prepared by compacting the soil at optimum water content conditions using the modified Proctor technique. Tests were performed under suction-controlled conditions by a stress path triaxial cell and an oedometer. The experimental program consists of 23 tests carried out in the suction range of 0-400 kPa. The findings indicate the strong influence of suction on compressibility, stiffness, and shear strength. The mechanical properties of the soil improve with suction following an exponential law with decreasing gradient. Furthermore, the soil exhibited collapsible behaviour upon wetting even at low stress levels. Interesting results were also achieved in elastoplastic modelling as well. The results led to characterization of soil behaviour with reference to widely accepted modelling criteria for unsaturated soils, providing noteworthy suggestions about their applicability for granular materials with a non-negligible fine component. Finally, some remarks are made for the extension under unsaturated conditions of the "Nor sand" model for saturated granular soils. The proposed approach yields improved predictions of deviator soil response of the tested soil when Cambridge-type frameworks prove invalid.Key words: unsaturated soils, stress state variables, triaxial tests, oedometer tests, constitutive model.
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9

Lopes, Elis Ferreira, Marcela Moreira da Rocha Moreira, Rosiel Ferreira Leme, and Francisco Chagas da Silva Filho. "Evaluation of settlement of shallow foundations laid on unsaturated soils." MATEC Web of Conferences 337 (2021): 03005. http://dx.doi.org/10.1051/matecconf/202133703005.

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The study presents an experimental and numerical study on an unsaturated, non-plastic and poorly graded sand, originated from Fortaleza-CE, Brazil. The numerical analyses used the Finite Element Method (FEM), were performed using the UNSTRUCT software to simulate the curve stress versus strain, considering the effect of suction on soil stiffness. Characterization and determination of the retention curve were performed through filter paper tests, which were used to determine the stress versus strain curve in a double-oedometer test. Suction was considered constant along the entire test. From the numerical analyses done with UNSTRUCT software presented satisfactory results, especially in the presence of suction profiles, that show the variation of suction along of the depth. It can be concluded that higher suction values (and soil stiffness) generate lower settlements.
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10

Jotisankasa, Apiniti, Andrew Ridley, and Matthew Coop. "Collapse Behavior of Compacted Silty Clay in Suction-Monitored Oedometer Apparatus." Journal of Geotechnical and Geoenvironmental Engineering 133, no. 7 (July 2007): 867–77. http://dx.doi.org/10.1061/(asce)1090-0241(2007)133:7(867).

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11

Cokca, Erdal. "Comparison of suction and oedometer methods for the measurement of swell pressure." Quarterly Journal of Engineering Geology and Hydrogeology 33, no. 2 (May 2000): 141–47. http://dx.doi.org/10.1144/qjegh.33.2.141.

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12

Zhang, Xiong, Haijun Lu, and Lin Li. "Use of Oedometer Equipped with High-Suction Tensiometer to Characterize Unsaturated Soils." Transportation Research Record: Journal of the Transportation Research Board 2578, no. 1 (January 2016): 58–71. http://dx.doi.org/10.3141/2578-07.

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13

Suits, L. D., T. C. Sheahan, Bertrand François, and Lyesse Laloui. "An Oedometer for Studying Combined Effects of Temperature and Suction on Soils." Geotechnical Testing Journal 33, no. 2 (2010): 102348. http://dx.doi.org/10.1520/gtj102348.

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14

Villar, M. V. "Investigation of the behaviour of bentonite by means of suction-controlled oedometer tests." Engineering Geology 54, no. 1-2 (September 1999): 67–73. http://dx.doi.org/10.1016/s0013-7952(99)00062-9.

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15

Mohammad, Thurgam A., and Laith J. Aziz. "Investigation settlement for unsaturated soil AL-NAJAF upon matric suction and different loading using Oedometer." Journal of Physics: Conference Series 1973, no. 1 (August 1, 2021): 012196. http://dx.doi.org/10.1088/1742-6596/1973/1/012196.

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16

Alcantara, Arisleidy Mesa, Nadia Mokni, Enrique Romero, and Sebastià Olivella. "Modelling of oedometer tests on pellet-powder bentonite mixtures to support mock-up test analysis." E3S Web of Conferences 195 (2020): 04004. http://dx.doi.org/10.1051/e3sconf/202019504004.

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Bentonite mixtures of MX-80 (80% of high-density pellets and 20% of bentonite powder on a mass basis) have been recently proposed as a candidate material for sealing deep geological disposals of high-level radioactive waste. A loading/unloading oedometer test at constant water content has been performed on this mixture, which has been modelled using the finite element Code_Bright. The constitutive model used to represent the mechanical response is the Barcelona Expansive Model (BExM), since a multi-modal pore size distribution characterises the pore network of the mixture. During compression at constant water content, an increase in the degree of saturation and a consequent reduction of suction is induced. Consequently, two competing effects occur at different pore-size scales: (a) compression due to mean net stress increase; and (b) expansion on induced suction reduction that mainly affects the micro-porosity level inside aggregates. A sensitivity analysis has been performed to explore these effects, in which the elastic compressibility parameter at the micro-porosity scale for changes in mean effective stress plays an important role.
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17

Rao, Sudhakar M., and T. Thyagaraj. "Swell–compression behaviour of compacted clays under chemical gradients." Canadian Geotechnical Journal 44, no. 5 (May 1, 2007): 520–32. http://dx.doi.org/10.1139/t07-002.

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The present study examines the effect of inflow of sodium chloride solutions on the swell–compression behaviour of compacted expansive clays under a range of external loads. Inflow of sodium chloride solutions reduced the swell magnitudes and pressures and even caused the compacted clay specimens to experience compressive strains in oedometer tests. The axial strain difference of specimens inundated with sodium chloride solutions and distilled water at a constant effective stress predicted the osmotic consolidation strains of a saturated clay specimen from an increase in osmotic suction in the pore fluid. Specimens exposed to larger osmotic suction gradients (Δπ) are predicted to experience larger osmotic consolidation strains. The predicted osmotic consolidation strains exceeded the experimental osmotic consolidation strains. The free-swell and load method and the swell under load procedure predicted different swell pressures owing to differences in strain contributions at the microstructure and macrostructure levels. The increase in osmotic suction in pore water apparently acts as an equivalent net stress (ρπ) that favours a reduction in swell potential of the compacted clay specimens due to a reduction in reversible swelling strains from an increase in net stress and irreversible macrostructural component that decreases because the distance of the stress point to the load–collapse (LC) curve decreases.Key words: compacted clays, chemical gradients, osmotic consolidation, suction, swell.
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18

Le, Trung Tinh, Yu-Jun Cui, Juan Jorge Muñoz, Pierre Delage, Anh Minh Tang, and Xiang-Ling Li. "Studying the stress-suction coupling in soils using an oedometer equipped with a high capacity tensiometer." Frontiers of Architecture and Civil Engineering in China 5, no. 2 (May 12, 2011): 160–70. http://dx.doi.org/10.1007/s11709-011-0106-x.

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19

Airò Farulla, Camillo, Alessio Ferrari, and Enrique Romero. "Volume change behaviour of a compacted scaly clay during cyclic suction changes." Canadian Geotechnical Journal 47, no. 6 (June 2010): 688–703. http://dx.doi.org/10.1139/t09-138.

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The research presented in this paper focuses on the investigation and modelling of the volume change response of compacted tectonised clay samples subjected to several wetting and drying cycles in controlled-suction oedometers. Oedometer tests were carried out under different values of constant vertical net stress, and wetting and drying cycles were performed varying applied matric suction between 10 and 800 kPa. The investigation was complemented with a study of the material microstructure to support the interpretation of the overall mechanical response. At a microscopic level, the material is characterized by different types of particle assemblages, scales, and clay aggregates. One of these assemblages was also subjected to a relative humidity cycle in an environmental scanning electron microscope (ESEM) to investigate the reversibility of the mechanical response. Based on the experimental results, the clay volume change behaviour is discussed and interpreted within the context of a double structure elastoplastic model. The procedure used to derive elastic and plastic constitutive parameters is presented. Comparison of test results with model predictions shows a satisfactory agreement between measured and calculated strain evolution.
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20

Burton, Glen J., Daichao Sheng, and David Airey. "Experimental study on volumetric behaviour of Maryland clay and the role of degree of saturation." Canadian Geotechnical Journal 51, no. 12 (December 2014): 1449–55. http://dx.doi.org/10.1139/cgj-2013-0332.

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In this paper, the volume change behaviour of Maryland clay compacted on the wet side of standard Proctor optimum water content (with lower compaction energy) is studied in reference to the saturated reconstituted state. Oedometer tests over a range of suctions and vertical stresses have been carried out, and the results have shown that the compression index reaches a peak (approximately twice that of the reconstituted material) and then gradually reduces to the reconstituted value as the stress level is increased. The results are analyzed in a framework where the degree of saturation is treated as a state parameter and controls the slope of the unsaturated normal compression line. Tests conducted under constant suction and constant water content have been used to demonstrate the effectiveness of using the degree of saturation as a state variable.
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21

Cui, K., P. Défossez, Y. J. Cui, and G. Richard. "Quantifying the effect of matric suction on the compressive properties of two agricultural soils using an osmotic oedometer." Geoderma 156, no. 3-4 (May 2010): 337–45. http://dx.doi.org/10.1016/j.geoderma.2010.03.003.

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22

Kyokawa, Hiroyuki. "Constitutive model describing the hydro-mechanical behaviors of compacted bentonite clay based on the crystal surface phenomena." E3S Web of Conferences 205 (2020): 04012. http://dx.doi.org/10.1051/e3sconf/202020504012.

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A constitutive model for unsaturated expansive soil based on the crystal surface phenomena is proposed. The behavior of the proposed model is described as a double structure, with the soil skeleton and the interlaminar behaviors. The soil skeleton behavior is modeled by the Cam clay type model based on the Bishop’s effective stress, which can consider the degree of saturation-induced hardening and inelastic behavior in the over-consolidated region and is capable of describing hydraulic collapse. On the other hand, the interlaminar behavior is give as a result of the interlaminar equilibrium of clay minerals. The diffusion double layer repulsive force in the interlaminar equilibrium varies with the degree of saturation, and it mainly causes the hydraulic swelling of expansive soil. The performance of the model is validated through the simulations of the suction-controlled oedometer tests on the heavily compacted bentonite.
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23

Liu, Zhengnan, Rui Zhang, Zhaojing Liu, and Yuming Zhang. "Experimental Study on Swelling Behavior and Its Anisotropic Evaluation of Unsaturated Expansive Soil." Advances in Materials Science and Engineering 2021 (May 25, 2021): 1–13. http://dx.doi.org/10.1155/2021/6937240.

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Evaluation of swelling behavior is important for designing structures in expansive soils areas, especially for highway that the swelling pressure generated upon pavement and retaining structures in both vertical and horizontal directions due to infiltration. In this study, modification was made on unsaturated consolidation oedometer to provide synchronized measurement of vertical swelling strain (VSS) and lateral pressure (LP) of expansive soil under constant net normal stress and controlled matric suction. Vertical swelling (VS) test and lateral swelling (LS) test were conducted to investigate the anisotropic swelling behavior. The influence of mean net stress and net stress ratio on VSS was investigated, and the anisotropic swelling behavior of unsaturated expansive soil was characterized using anisotropic swelling ratio. The results show that the VSS nonlinearly decreased as the mean net stress increased and increased as the net stress ratio increased. The expansive soil would rapidly enter the passive state due to lateral swelling pressure under relatively low surcharge, with major principal axis rotating from vertical direction to lateral direction, which advances the possibility of passive failure for light retaining structures. The anisotropic swelling behavior objectively exists and varies with matric suction and net normal stress, which should not be ignored for engineering application.
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24

Houston, Sandra, and Xiong Zhang. "Review of expansive and collapsible soil volume change models within a unified elastoplastic framework." Soils and Rocks 44, no. 3 (July 8, 2021): 1–30. http://dx.doi.org/10.28927/sr.2021.064321.

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Numerous laboratory tests on unsaturated soils revealed complex volume-change response to reduction of soil suction, resulting in early development of state surface approaches that incorporate soil expansion or collapse due to wetting under load. Nonetheless, expansive and collapsible soils are often viewed separately in research and practice, resulting in development of numerous constitutive models specific to the direction of volume change resulting from suction decrease. In addition, several elastoplastic models, developed primarily for collapse or expansion, are modified by add-on, such as multiple yield curves/surfaces, to accommodate a broader range of soil response. Current tendency to think of unsaturated soils as either expansive or collapsible (or, sometimes, stable), has likely contributed to lack of development of a unified approach to unsaturated soil volume change. In this paper, common research and practice approaches to volume change of unsaturated soils are reviewed within a simple macro-level elastoplastic framework, the Modified State Surface Approach (MSSA). The MSSA emerges as a unifying approach that accommodates complex volume change response of unsaturated soil, whether the soil exhibits collapse, expansion, or both. Suggestions are made for minor adjustments to existing constitutive models from this review, typically resulting in simplification and/or benefit to some of the most-used constitutive models for unsaturated soil volume change. In the review of practice-based approaches, the surrogate path method (SPM), an oedometer/suction-based approach, is demonstrated to be consistent with the MSSA framework, broadly applicable for use with expansive and collapsible soils, and yielding results consistent with measured field stress-path soil response.
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Tripathy, Snehasis, Sahar Al-Khyat, and Peter John Cleall. "Impact of Single and Multiple Specimen Suction Control Oedometer Testing on the Measurement of the Soil–Water Characteristic Curve." Geotechnical Testing Journal 44, no. 6 (May 26, 2021): 20200341. http://dx.doi.org/10.1520/gtj20200341.

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26

Cardoso, Rafaela, Gabriele Sarapajevaite, Oleksandr Korsun, Susana Cardoso, and Laura Ilharco. "Microfabricated sol-gel relative humidity sensors for soil suction measurement during laboratory tests." Canadian Geotechnical Journal 54, no. 8 (August 2017): 1176–83. http://dx.doi.org/10.1139/cgj-2016-0419.

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Currently there are no small sensors that can be incorporated inside soil samples for laboratory testing, to monitor water transport during loading. This is an important limitation to a better understanding of the hydromechanical coupled behaviour of soils. A sol-gel relative humidity sensor (11 mm × 11 mm), microfabricated in a clean room environment, was conceived to be incorporated in soil specimens during standard laboratory tests. The sensor operates based on changes in electrical resistivity detected by a cerium-doped silica–titania film deposited using a sol-gel technique over interdigitated aluminium electrodes spaced at 300 μm. To the best of the authors’ knowledge, sol-gel sensors for relative humidity measurement have never been used in soils; therefore, this is a novel application. The water retention curve of compacted kaolin was measured with the sensors and compared with the curve found using water dewpoint potentiometer WP4-C. The sensors were also tested incorporated in an oedometer cell, in which load was applied under vapour equilibrium. It was possible to detect the increment of the degree of saturation during compression. The use of the developed sensors incorporated in soils is considered acceptable for suction ranges between 1 and 10 MPa, which extends the suction interval covered by tensiometers, normally operating up to 2 MPa. Although the sensors require improvements in terms of sol-gel deposition and calibration protocol, the results confirm their scientific potential for being used in testing and characterization of unsaturated soils.
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27

Roy, M., P. La Rochelle, S. Leroueil, J. M. Konrad, and G. Bergeron. "Effets de cycles de gel–dégel sur les propriétés d'une argile sensible." Canadian Geotechnical Journal 32, no. 4 (August 1, 1995): 725–40. http://dx.doi.org/10.1139/t95-070.

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A laboratory study of the evolution of the behaviour of a sensitive clay under many freeze–thaw cycles is presented; it follows the laboratory study of Leroueil et al. (1991) and the field study of Roy et al. (1992). The physical properties of the clay have been followed by means of consistency and permeability tests after each freeze–thaw cycle, and the mechanical behaviour has been assessed by means of falling cone, oedometer, and consolidated isotropically undrained triaxial tests. The changes in internal structure have been observed by means of the scanning electron microscope and the mercury porosimeter. The results show that the changes in properties are significant during the first three freeze–thaw cycles and hardly significant during the following cycles. The structure change can be explained by the high suction that develops during the generation of ice lenses behind the frost front. Key words : clay, freeze–thaw, shear strength, permeability, heaving, settlements. [Journal translation]
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28

Taylor, Oliver-Denzil S., Katherine E. Winters, Woodman W. Berry, Lucas A. Walshire, and Pamela G. Kinnebrew. "Near-surface soils: self-supported unconfined drained sand specimens." Canadian Geotechnical Journal 56, no. 3 (March 2019): 307–19. http://dx.doi.org/10.1139/cgj-2017-0261.

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Knowledge about soil behaviour in the near surface is fundamental to a broad range of military strategic research efforts. The prevailing mathematical representations of near-surface shear strength do not necessarily reflect the observed shear strengths. This paper presents an experimental procedure for testing self-supported, unconfined-drained specimens to investigate the shear strength of a poorly graded sand with the inferred unsaturated behaviour from typical effective stress expressions. The impact of soil suction is quantified from the soil–water characteristic curve obtained from a modified, unsaturated, one-dimensional oedometer device: Fredlund’s device. Seventy-seven unconfined tests illustrate that while individual or discrete states can be explained by effective stress relationships, those expressions do not accurately quantify the observed shear strength from one state to the next. Saturation failure is observed when the degree of saturation is between 70.5% and 76.5%, well below the assumed threshold. The results show that the dry shear resistance is a function of the initial density state, but as the degree of saturation increases, the shear resistance becomes independent of the initial density, and converges to the saturation failure. These findings expose the limitations of effective stress expressions and suggest a revised nonlinear, three-dimensional, unconfined Mohr failure envelope based on an applied external stress.
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29

Zhang, Tongwei, and Shijun Wang. "Explanation of the Influence of Sodium Chloride Solution on Volume Deformation and Permeability of Normally Consolidated Clays." Materials 12, no. 10 (May 22, 2019): 1671. http://dx.doi.org/10.3390/ma12101671.

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The marine clays located in the Southeast area of China are characterized by their higher water content, higher compressibility and higher salinities. This soil is mainly composed of illite/montmorillonite interlayer minerals. Previous research has shown that the saline water significantly influences the liquid limit and other physical characteristics of the clays. As the desalination of pore water occurs as a result of freshwater or rainfalls, the physical and mechanical behaviors of the soft marine clays changes, and this can lead to potential hazards for infrastructure. Therefore, it is essential to understand the effects of chemistry variations and to predict the long-term foundation deformations. Based on previous works, the deformation behavior of artificial soils corresponding to a mixture of kaolinite and bentonite (the mass ratios of bentonite were 0%, 5%, 10% and 20%) was further discussed in a ln(1 + e)-logp’ system. The permeabilities of the samples mixed with different concentrations of sodium chloride solutions were compared based on oedometer tests. The micro-structures in the samples were investigated by SEM (scanning electronic microscopy) tests. The declining trend of a newly defined volume compression index Ccv and swelling index Csv with pore water salinity and e0/eL was observed when the initial void ratios e0 of the samples were close. The permeability coefficient k and the slopes Ck = e/logk of the mixtures increased with the ionic concentrations. Finally, the changes in volume deformations and permeabilities induced by sodium chloride solution are discussed based on ‘suction pressure’ and initial void compression at micro-level. This paper proves that the influences of salinity on the mechanical behavior of clays are mainly attributable to the interaction between diffused double layers, and these findings are helpful for improving the constitutive model of soft clays when taking pore water chemistry changes into consideration.
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"Oedometer suction controlled tests (In French)." International Journal of Rock Mechanics and Mining Sciences & Geomechanics Abstracts 27, no. 6 (December 1990): 345. http://dx.doi.org/10.1016/0148-9062(90)91188-d.

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"Suction-controlled oedometer tests in montmorillonite clay: preliminary results." International Journal of Rock Mechanics and Mining Sciences & Geomechanics Abstracts 33, no. 6 (September 1996): A255. http://dx.doi.org/10.1016/0148-9062(96)81788-8.

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