Compression mechanisms of unsaturated clay under high stresses (original) (raw)
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Constitutive Model for the Undrained Compression of Unsaturated Clay
Journal of Geotechnical and Geoenvironmental Engineering, 2017
This paper proposes a constitutive model to describe the isotropic compression response of unsaturated, compacted clay under undrained conditions over a wide range of mean stresses. The total stress-based model captures the impacts of the initial degree of saturation on the apparent preconsolidation stress and the slope of the compression curve up to the point of pressurized saturation. The points of pressurized saturation for specimens with different initial degrees of saturation were predicted using a modified form of Hilf's pore pressure analysis. The compression response for pressure-saturated specimens was dominated by the pore water, although dissolved air and soil structure may play a role for some soils. The model was calibrated using results from a series of compression tests on compacted clay specimens having initial degrees of saturation ranging from 0.6 to 1.0 and the same initial void ratio. The model was found to provide a good match to the experimental data for mean stresses up to 160 MPa, in particular due to the improvements in Hilf's analysis to evaluate the points of pressurized saturation.
Agricultural Engineering International: The CIGR Journal, 2004
This paper reports experimental data gathered while performing isotropic tests on a heavy agricultural clay soil from Quebec province (Eastern Canada). Tests performed were onedimensional compression, isotropic compression, and K 0. Tests on saturated soil samples were performed using conventional procedures; tests on unsaturated samples were performed after the desired suction was applied to the samples. Samples used in all the tests were processed at the same suction before the selected suction was applied. For the one-dimensional compression tests, the chosen suction was applied by moistening or drying while the axis translation method was used for applying suction to soil samples in isotropic compression and K 0 tests. Results show that soil plastic and elastic parameters are suction dependant. In addition, strength of Sainte-Rosalie clay measured under different suctions in K 0 tests quantified the significant strength gain observed in the field when this material evolves from wet to dry conditions.
Stress-dependent behavior of saturated clay
Canadian Geotechnical Journal, 2012
A program of K0-consolidated undrained triaxial compression tests has been performed to investigate the effects of consolidation stress level on the compression and shear behavior of resedimented Boston blue clay (RBBC). Specimens were consolidated to maximum vertical effective stresses in the range 0.15–10 MPa and tested at three overconsolidation ratios (OCR): 1, 2, and 4. The results show that the virgin compression curves are essentially linear in e–log[Formula: see text] space over the consolidation stress range. However, the normally consolidated K0 stress ratio increases with the level of consolidation stress. The stress–strain–strength properties measured in undrained shear are significantly affected by the consolidation stress level at each OCR and show indications of non-normalizable behavior. At high pressures, the undrained shear stress–strain behavior becomes more ductile, requiring larger strains to mobilize peak resistance and exhibiting less post-peak strain-softenin...
Compression and Permeability Relationships in High Water Content Clays
Storing contaminant soils, such as dredge materials, sludge and mine tailings, and reclaiming contaminant soil storage areas back into the economy has arisen as an important economical and environmental problem in today's world. The scientific studies in the last thirty years have revealed critical new information regarding the deformation behavior of high water content soils. In this article relationships between material properties used in constitutive models for self-weight and/or surcharge loaded high water content (slurry) clays and their index properties are investigated. For this purpose three different kinds of clays in a slurry consistency are subjected to seepage induced consolidation in an experimental setup. Information obtained from these experiments, together with information already in literature, is used to investigate the relationships between the index properties and the consolidation constitutive model parameters. The relationships obtained from the experiments are then utilized to predict the self-weight consolidation of Halic (Golden Horn) dredge materials. These predictions are then compared with the results of numerical analysis and found to be in good agreement.
Rate effects on the undrained shear strength of compacted clay
Soils and Foundations
Unconsolidated-undrained (UU) triaxial compression tests were performed on low-4 plasticity clay specimens compacted to the same void ratio but different initial degrees of 5 saturation to evaluate the impact of axial strain rates ranging from 0.1 to 150 %/min on the 6 undrained shear strength. Although an effective stress analysis cannot be performed on the 7 results, they are useful to evaluate the relative roles of initial hydraulic conditions (i.e., matric 8 suction and degree of saturation) and compaction effects (i.e., potential changes in soil structure 9 with compaction water content). This evaluation is relevant due to difficulty in measuring shear-10 induced pore water and air pressures in consolidated-undrained (CU) compression tests on 11 unsaturated clay. In all tests, the undrained shear strength quantified as the maximum principal 12 stress difference increased log-linearly with axial strain rate, with rates of increase ranging from 13 4.1 to 9.7% per log cycle of axial strain rate for specimens having initial degrees of saturation 14 ranging from 0.99 to 0.59. The undrained shear strength, rate of increase in undrained shear 15 strength with axial strain rate, and secant moduli all increased nonlinearly with decreasing initial 16 degree of saturation, although compaction effects played an important role in these trends. The 17 increase in undrained shear strength with axial strain rate can be attributed to a reduction in the 18 magnitude of excess pore water pressure, with similar reductions in magnitude for all the degrees 19 of saturation considered. A comparison between the measured undrained shear strength values 20
SOILS AND FOUNDATIONS, 2011
A simple but automated pneumatic loading system that can control the stress and strain rates for one-dimensional (1D) compression of clay was developed. The rate-dependency of stress-strain behaviour due to the viscous property of clay was investigated by 1D compression tests on standard-size specimens by various loading methods: 1) Standard Consolidation Tests (SCTs), stepwise increasing the axial stress two times every one day; 2) ordinary Constant-Rateof-Strain (CRS) tests at diŠerent strain rates; 3) special CRS tests including unloading and reloading cycles with diŠerent stress amplitudes at strain rates of which the absolute value was either kept constant throughout respective tests or changed at the start of reloading; and 4) special CRS tests including a number of sustained loading (SL) during otherwise primary loading or unloading or reloading at constant strain rate. Su‹ciently low strain rates were employed to ensure essentially fully drained condition. The followings were found. Despite that the newly developed pneumatic loading system is rather simple, 1D compression tests following such various loading histories as above can be performed on four types of clay rather accurately. The stress-strain behaviour of clay is signiˆcantly rate-dependent, exhibiting signiˆcant creep strains at SL stages. The creep strain rate is signiˆcantly diŠerent whether SL starts during otherwise primary loading or unloading or reloading, controlled by the magnitude and sign of the initial strain rate at the start of SL. The whole observed trends of rate-dependent stress-strain behaviour can be qualitatively explained by the non-linear three-component elasto-viscoplastic model extended to cyclic loading conditions.
Effect of stress ratio on the volume change behavior of compacted highly expansive clay
Arabian Journal of Geosciences, 2016
This paper aims at emphasizing the influence of stress conditions on the volume change behavior of expansive soils. A series of triaxial tests were conducted on remolded highly expansive clay specimens inundated under different combinations of stress ratios, K (ranging between 0.5 and 1.45) and axial inundation stress, σ ai (ranging between 50 and 800 kPa). Volume change characteristics obtained from these tests included axial inundation strain (ε ai), volumetric inundation strain (ε vi), and axial swelling pressure (σ s). Results of the experimental program showed that the stress ratio had a significant effect on magnitude of axial inundation strain. Test results revealed that axial inundation strain decreased with increase in axial inundation stress. However, stress ratio had a negligible effect on the volumetric inundation strain-mean inundation stress relationship. Furthermore, the axial inundation strain and axial swelling pressure obtained from triaxial tests were compared with that obtained from one-dimensional oedometer tests conducted on identical specimens and applied axial stress. The differences between axial inundation strain and axial swelling pressure evaluated from triaxial and oedometer testing were quantified by using corrections factors. Using these correction factors, a systematic procedure was proposed for the realistic estimation of axial inundation strain in the field based on results of laboratory oedometer tests and knowledge of in situ axial stress and stress ratio.
Rate dependency and Stress Relaxation of Unsaturated Clays
3 This paper presents the experimental program conducted for evaluation of the rate-dependent 4 and stress-relaxation behaviour of unsaturated reconstituted London Clay. A series of drained 5 constant rate of strain (CRS) compression-relaxation tests with single-staged (SS-CRS) and 6 multi-staged (MS-CRS) loading modes were performed in an innovative CRS oedometer cell 7