Strength Of Granular Soils Research Articles

UH model for granular soils considering low confining pressure

The mechanical behaviors including strength and isotropic compression of granular soils under low confining pressure are systematically analyzed. The compressive hardening parameter ps is introduced in semi-logarithmic coordinates to express the curved normal compression line of granular soils in the e-ln p plane, to describe the little compressibility of granular soils under low confining pressure. The nonlinear variation of critical friction angle with confining pressure is considered by introducing the interlocking strength parameter τ0 into strength criteria. Based on the unified hardening model for clays and sands (CSUH model), the unified hardening (UH model) for granular soils considering low confining pressure, called UH-L model, is established. The UH-L model behaves significantly different with the CSUH model under low confining pressure, while tends to be same as the CSUH model with increasing confining pressure. The relationship between parameter ps and τ0cotφ, as well as the effect of ps and τ0cotφ on model performance are analyzed. Good agreement with the experimental data shows that the UH-L model is capable of uniformly describing the stress–strain relations and strength of granular soils with interparticle locking over a wide confining pressure load range, especially at low confining pressure.

Explanations of anisotropic strength and fabric evolution in granular soils by DEM simulations and buckling failure theory

ABSTRACT This research aims to discover a micro explanation of anisotropic strength of granular soils caused by different inherent fabrics based on the discrete element method (DEM) simulations. Soil particles are simulated as ellipsoids (i.e., clumped spheres) to preserve the elongation distributions of real soil particles that are determined by analysing 90,000 particles from 18 sands. Then, virtual soil specimens are prepared at 12 different inherent fabrics by restricting the particle long axis orientations. For each inherent fabric, triaxial tests are simulated at five intermediate stress ratio values, resulting in a total of 60 DEM simulations. The relationships between anisotropic shear strength and fabric evolution are investigated based on simulation results. For a specific inherent fabric, Lade’s isotropic failure theory can be used to describe shear strengths and octahedral contact normal fabric factors at peak and critical states. A buckling failure theory from structural engineering is introduced to explain the anisotropic strength of granular soils and fabric evaluations observed in laboratory tests and simulations. As the angle between loading and fabric direction increases from zero to 90 degrees, the conceptual widths of soil columns decrease, leading to the smaller buckling failure loads and therefore the smaller shear strength of granular soils.

Shear strength of granular soils from the simulation of dynamic penetration tests

Abstract This paper presents a model for the numerical simulation of dynamic penetration tests in cohesionless soils. In the model, dynamic penetration equations are solved by finite difference analysis in the time domain to produce the discretization of the penetration system. The approach allows essential effects of the soil influence to be accounted for, including the dynamic soil resistance by viscous damping during penetration. The model performance has proved by comparisons between the static and dynamic resistance to reproduce the variation with time of measured force, velocity, displacement and energy associated with the interaction mechanism around split-spoon samplers when penetrating in the ground. A realistic representation of the dynamic penetration mechanism allows the internal friction angle of the soil to be estimated. The proposed methodology accounts for scale effects and produces values of φ′ within the same order of magnitude as those estimated from piezocone test data.

Behavior of square footing on dune sand reinforced with nylon fiber

Dune sand covers a large part of the world's desert. It is uniformly graded fine sand deposited by wind action. Geotechnical engineers face various problems in dealing with such soils as it has poor bearing capacity, high permeability and low shear strength etc. Reinforcing the soil with randomly distributed discrete fibers increases the shear strength of granular soil. The present paper deals with the laboratory tests on the use of nylon fibers as a means to enhance the bearing capacity of dune sand. A series of load tests were conducted on a mixture of dune sand and nylon fiber to determine various factors which influence the bearing capacity of dune sand nylon fiber mixtures. The amount of nylon fiber, added to dune sand, as 0.5%, 1.0%, 1.5% and 2%. The size of square footing and depth up to which nylon fiber were mixed varied and the load settlement behavior of square footings on dune sand reinforced with nylon fiber were recorded. The results of settlement behavior were interpreted with bearing capacity characteristics, bearing capacity ratio, settlement characteristics at constant load intensity and load intensity at constant settlement. The ultimate bearing capacity of dune sand reinforced with nylon fiber increases with nylon fiber content. Also, the ultimate bearing capacity increases with <i>H/B</i> ratio, where <i>H</i> is height of reinforced soil and B is the width of square footing.

Steady State Strength of Sands in a Constant Volume Ring Shear Apparatus

Abstract A modified volume ring shear test apparatus has been developed to undertake constant volume ring shear tests on sand. This constant volume test is a useful means of assessing the steady state strength of granular soils at large strain to determine the liquefaction potential of a soil mass. The apparatus and specimen preparation tools and methods are presented herein. The paper also presents the device and method used to verify the uniformity of the specimens prepared and the repeatability of the specimen preparation method. An experimental program has been conducted using both constant volume (CV) and constant load (CL) tests to investigate the effect of saturation, and of fines on the steady state line (SSL) and the steady state strength (SSS) envelope.