Stress-strain Behavior Of Sand Research Articles

The role of breakage-dependent critical state lines in constitutive modelling of sand under axisymmetric drained and undrained loads: A comparative study

Particle breakage usually takes place within sand when subjected to external loading, which changes the critical state line (CSL) and stress-strain behavior of sand. To consider such effect, different expressions for the CSL with consideration of particle breakage have been proposed, which can be sorted in two categories: (i) CSL through explicit incorporation of particle breakage ratio into the e – ln p′ relation, (ii) CSL through implicitly empirical correlation, e.g., e – p′ 0.7 and e – exp(p′ζ ) relations. However, limited studies were made on comparing the performances of these expressions. This study inspects the efficiency of three representative CSLs from categories i and ii, for SANISAND modelling of sand. It was found that all the CSLs can capture the constitutive responses of sands under axisymmetric drained and undrained loads, to some extent. However, e – p′ 0.7 and e – exp(p′ζ ) relations are comparatively simple and share an equivalently accurate performance at low to medium high pressures, whereas e – exp(p′ζ ) relation works the best among others at high pressures. To more highlight the physical role of particle breakage, the CSL in category i can be suggested. Otherwise, the CSLs in category ii are recommended in modelling practices, because of the comparatively succinct expressions and less model parameters.

Post-liquefaction deformation and strength characteristics of sand in torsional shear tests

The estimation of strength deterioration with the increase in the undrained cyclic shear-induced strain in liquefiable soils is an important topic in geotechnical earthquake engineering that is still poorly understood and needs to be properly addressed. In this paper, in an attempt to provide new insights into this topic, the post-liquefaction undrained strength and deformation of Toyoura sand were investigated through a series of laboratory tests performed by using a large-strain torsional shear apparatus. In the tests, simple shear conditions were reproduced on a medium-size hollow cylindrical specimen to apply stress conditions that soil experiences in the field during earthquakes. Specimens prepared by the air-pluviation method were first liquefied by applying a constant amplitude undrained cyclic shearing to induce a target cyclic shear-induced damage strain (γΔ). The tests were terminated at different amplitudes of γΔ and subsequently loaded monotonically in undrained conditions to obtain stress-strain and excess pore water generation responses. The test results indicate that the post-liquefaction monotonic loading (ML) stress-strain behavior of sand can be divided into three regions, namely Region 1, 2 and 3. The sand behavior changes to strain-hardening from essentially zero strength and stiffness from Region 1 to 2. While Region 3 marks the beginning of strain-softening state in the sand. It is found that the strain localization is associated with the transition of sand behavior from strain-hardening to strain-softening state. It is proposed that the sand undrained strength in monotonic shearing is the true representation of specimen response until the state of uniform deformation is maintained, based on the sudden drop of the differential stress (σd = σ v′ - σh′). The test results also revealed that there is a progressive degradation in the shear strength with the increase in the amplitude of γΔ. A correlation depicting the degradation ratio (τd) with the increase in the γΔ is proposed. This correlation can be used to estimate the degree of degradation with the increase in the applied γΔ, and it is valid for different density states, confining stresses and cyclic stress ratios.

Experimental investigation of the influence of bedding planes on the mechanical characteristics of saturated sand

This paper presents an experimental study concerning the relevance of mechanical characteristics and bedding planes of sand. The study was carried out using a new method of specimen fabrication based on the capillary effect. A series of triaxial tests were performed to study the stress-strain behavior of sand under different bedding plane tilting angles. The results show that the peak deviatoric stress and the volumetric strain are significantly different under different bedding plane tilting angles due to the inherent anisotropy of sand, and the difference between their peak strengths can reach 30%. The specimen reached the failure stage more easily and the peak strength was lower, reaching the residual state earlier when the bedding plane tilting angle was close to 45°-ϕ/2. The equation proposed in this study can thus reasonably reflect the relationship between the bedding plane tilting angle and the peak strength. The inherent anisotropy due to the bedding plane of sand may have a significant influence on the deformation of building foundations; therefore, neglecting this factor may lead to unsafe designs.

Numerical Modeling on the Stress-Strain Behavior of Sand via Disturbed State Concept Model

The disturbed state concept (DSC), proposed by Desai, is a powerful constitutive modeling for the simulation of the material behaviors of strain hardening or softening of soil. These material parameters can be decided by the results of the triaxial compression test of soil. Some triaxial drained test were performed to obtain the deviator stress vs. axial strain behaviors of Ottawa sand with relative densities Dr ＝20% and 90% under three different confining pressures. The result shows that the experimental data and the results of the DSC model showed good correspondence. In study for disturbance parameters to effect on the curve of axial strain vs. deviator stress, it can be found that the deviator stress after peak markedly decreases when the values of disturbance parameters are reduced. The effect of disturbance parameter A on the trend for deviator stress decrease after peak is higher than that of parameter B.

Effect of initial relative density on the post-liquefaction behaviour of sand

Understanding the behaviour of soils under cyclic/dynamic loading has been one of the challenging topics in geotechnical engineering. The response of liquefiable soils has been well studied however, the post liquefaction behaviour of sands needs better understanding. In this paper, the post liquefaction behaviour of sands is investigated through several series of multi-stage soil element tests using a cyclic triaxial apparatus. Four types of sand were used where the sands were first liquefied and then monotonically sheared to obtain stress-strain curves. Results of the tests indicate that the stress-strain behaviour of sand in post liquefaction phase can be modelled as a bi-linear curve using three parameters: the initial shear modulus (G1), critical state shear modulus (G2), and post-dilation shear strain (γpost−dilation) which is the shear strain at the onset of dilation. It was found that the three parameters are dependent on the initial relative density of sands. Furthermore, it was observed that with the increase in the relative density both G1 and G2 increase and γpost−dilation decreases. The practical application of the results is to generate p-y curves for liquefied soil.

Effect of Strain Rate on the Stress-Strain Behavior of Sand

Drained triaxial compression tests on crushed coral sand were performed from near-static strain rates to very high strain rates (up to approximately 1,800%/s). Experiments were performed on dry, vacuum-confined axisymmetric specimens at two different confining pressures (98 and 350 kPa) and two different densities (Dr approximately 36 and 60%). A gravity drop weight loading system was used to generate high strain rates. High-speed film photographs of the specimen were taken through the flat sides of a square triaxial cell. By using digital image analysis techniques, strains were locally measured near the center of the specimen to obtain the most uniform assessment. Stress-strain relationships are presented. The following effects were observed with increasing strain rates: the elastoplastic stiffness increased significantly; the failure shear strength increased moderately; the axial strain at peak stress decreased significantly; and volumetric strains became more dilatant. Unusual behavior was observed at ...

Effect of Specimen Preparation Method on the Stress-Strain Behavior of Sand in Plane-Strain Compression Tests

Abstract Experimental results are presented in this paper to study the effect of specimen preparation method on the stress-strain behavior of sand in plane-strain compression tests. The data obtained from K0 consolidation, drained, undrained and strain path tests conducted on medium loose specimens prepared by the moist-tamping (MT) and the water sedimentation (WS) methods are compared. The test data show that the plane-strain compression behavior of medium loose sand under K0, drained and strain-path controlled (including undrained) conditions is affected by the specimen preparation method. Under K0 conditions, the K0 values obtained from the MT specimens are generally lower than those obtained from the WS specimens. Under drained conditions, more contractive behavior was observed for the MT sand. However, the failure stress ratio (or the failure friction angle) was not affected by the specimen preparation method. The data presented in this paper also illustrate that the compression behavior of medium loose sand in strain-path testing can be affected by the specimen preparation method. However, the differences in the stress-strain behavior will also depend on the strain increment ratio (dεv/dε1) imposed on the specimens. In general, different behaviors of the moist-tamped and water-deposited specimens reflect the influence of soil fabrics on the stress-strain behavior of sand.

Dynamic deformations in sand embankments: centrifuge modeling and blind, fully coupled analyses

Prediction of deformations during earthquake loading is one of the critical aspects in the design of a geotechnical engineering structure. The dynamic behavior of two centrifuge model sand embankments including deformations is presented and compared with blind predictions made by a fully coupled analysis procedure, the computer code DYSAC2, using a bounding surface elastoplastic model. The centrifuge model embankments were constructed using Nevada sand placed at 62% (dense) and 43% (medium dense) relative densities and consisted of a mild slope on one side and a steep slope on the other side. Both embankments showed substantial movements along the slopes, spikes in the upslope acceleration values, and corresponding dilation spikes in the pore-pressure values. These spikes were more pronounced for the medium-dense sand embankment and on the mild-slope sides for both embankments. The observed behavior is related to the stress–strain behavior of sands undergoing cyclic mobility, and the importance of accurately obtaining the initial static stresses is emphasized. The blind predictions using the computer code DYSAC2 compared reasonably well with the measured results and provided further insight into the behavior of these embankments. The blind predictions similar to those shown in this paper are expected to provide confidence for practicing engineers to use fully coupled procedures for predicting deformations of geotechnical structures subjected to earthquakes.Key words: centrifuge modeling, cyclic mobility, earthquakes, embankment, fully coupled analysis, sand.

Experimental compression of loose sands: relevance to porosity reduction during burial in sedimentary basins

This study examines the one-dimensional stress–strain behaviour of sand at effective stresses as high as 50 MPa. Experiments were performed on 22 sands (approx. 150 tests) with different grain size, uniformity coefficient, angularity, density, grain mineralogy, and clay content. The results show that minor grain corner crushing starts at stresses of 2–8 MPa. The point of maximum curvature (yield point) in the porosity (n) versus logarithm of vertical effective stress (σ'v) curve defines the initiation of marked particle crushing. The stress at the yield point varies between 3 and 31 MPa depending on sand characteristics. A low yield stress is indicative of high porosity loss in the interval of intermediate stress (5–25 MPa). The yield stress is low when the grain size is large, grains are angular, grain strength is low, and uniformity coefficient is low. The lowest yield stress value occurs in the coarser carbonate sand, and the highest in the chert-rich sands. The sands rich in clays are highly compressible up to 25 MPa. At stresses higher than ~10 MPa, the coarser biogenic carbonate sands maintain higher porosities than the other sands. This can be explained by the fact that coarser biogenic carbonate sands have low yield stresses due to high angularity and low grain strength and initially there is local grain crushing at grain contacts. This increases the area of the grain contacts, so the coarser carbonate sands become less compressible at higher stresses. Within the high stress range (25–50 MPa) the porosity loss differences related to grain size, grain shape, grain mineralogy, and sand uniformity coefficient are significantly reduced. Hence the greater compressibility of lithic and carbonate sands becomes less evident in the high-stress interval as the grain size increases.Key words: sand, grain crushing, grain size, high stress, compression.

Undrained Anisotropic Monotonic Behavior of Sand from In Situ Tests

A procedure for estimating the undrained stress-strain behavior of sand from drained self-boring pressuremeter and seismic piezocone penetration tests is proposed in this paper. The procedure offers an inexpensive alternative to laboratory testing and avoids the uncertainty of the empirical methods based on index measurements such as the Standard Penetration Test blow count and the tip resistance in a Piezocone Penetration Test (CPTU). To check its validity, the proposed procedure was used to infer the undrained triaxial stress-strain curves and the results were compared with laboratory triaxial tests on undisturbed samples. The undrained limit equilibrium stability of a dike was also assessed using the inferred stress-strain behavior to illustrate the usefulness of the procedure. The result of the stability analysis was found to be in qualitative agreement with the observed performance of the dike during a recent field experiment attempting to trigger static liquefaction.

Stress-Strain Behavior of Sand in Plane Strain Compression, Extension and Cyclic Loading Tests

Stress-strain behavior of sand in plane strain compression, extension and cyclic loading was studied. To attain plane strain extension stress states in a conventional plane strain compression apparatus, a pair of intermediate confining platens were added between the specimen and the conventional confining platens. They together were enveloped within a specimen membrane so that the intermediate principal stress can be larger than the vertical stress under plane strain extension stress conditions with the lateral confining pressure larger than the vertical stress. To simulate active and passive earth pressure conditions and those under horizontal cyclic loading conditions with the constant vertical stress in the field, specimens were rotated by 90 degrees before each test so that the horizontal stress when the specimen was prepared became the vertical stress in the test. Typical stress-strain relationships are presented from tests performed on saturated specimens of air-pluviated Toyoura sand measuring strains locally. It is shown that although the relationships between the vertical stress and the vertical strain are considerably non-symmetric about the neutral stress condition under the plane strain compression and extension stress conditions, those between sin and the shear strain are essentially symmetric, and therefore, relevant for modeling. Stress-dilatancy relationships are also presented.

Erratum for “Stress-Strain Behavior of Sand”

Erratum for “Stress-Strain Behavior of Sand”

Stress-strain behaviour of sand : Khosla, VK Wu, TH Herron testing, Cleveland, Ohio, USA Ohio State Univ., Columbus, USA 21F, 2T, 34R. J. Geotech. Engng Div. Asce, V102, GT4, 1976, P303–321

Stress-strain behaviour of sand : Khosla, VK Wu, TH Herron testing, Cleveland, Ohio, USA Ohio State Univ., Columbus, USA 21F, 2T, 34R. J. Geotech. Engng Div. Asce, V102, GT4, 1976, P303–321

Stress-Strain Behavior of Sand

The paper presents results of laboratory static and cyclic loading tests on Ottawa Sand. A variety of stress paths was used. The results are analyzed by elastic-plastic-work hardening theory. It is shown that the Mohr-Coulomb failure criterion, combined with an expanding elliptical cap can satisfactorily represent material behavior. The proposed model makes it possible to predict soil response to diverse stress paths from the results of hydrostatic compression and drained triaxial compression tests. The model is applicable to material behavior under both static and cyclic loading.

Boundary conditions, anisotropy and sample shape effects on the stress-strain behaviour of sand in triaxial compression and plane strain. 16F, 1T, 22R : Green, GE Shannon and Wilson, Seattle, USA Reades, DW Promon Eng. SA, Rio de Janeiro, RA Geotechn, V25, N2, June, 1975, P333–356

Boundary conditions, anisotropy and sample shape effects on the stress-strain behaviour of sand in triaxial compression and plane strain. 16F, 1T, 22R : Green, GE Shannon and Wilson, Seattle, USA Reades, DW Promon Eng. SA, Rio de Janeiro, RA Geotechn, V25, N2, June, 1975, P333–356

Yielding and Locking of Confined Sand

Experimental results of the stress-strain behavior of sand during confined compression, starting from some initial stress, show that the stress-strain curve is S-shaped, with yielding for small stress changes and locking as the stress change is increased further. In addition, the modulus during small stress changes is found to be consistent with the modulus backfigured from seismic wave velocity. Theory for the behavior of a regular array of elastic spheres is used to help explain these results. The effect of rate of loading is shown by experiment. On the basis of these findings, either plastic or shock waves can occur in sand, depending on the magnitude of the initial stress and the stress change. The modulus of compression during a dynamic loading can be significantly less than indicated by seismic velocity.