Distinct element simulation was performed for direct shear box (DSB) tests on a dense and a loose two-dimensional (2D) sample of 3259 cylinders. Special attention was devoted to the effect that the frictional force between the inside surface of the upper shear box and the sample had on the measured shear strength in the DSB test. Some ways of minimizing this interface frictional force were introduced in the paper. Given that the deformation approximates simple shear within the deforming zone across the sample centre (referred to as the shear zone), a method was proposed to evaluate the overall strains in the DSB test. The numerically simulated data were used to interpret, on a microscopic scale, the angle of internal friction and a 2D stress-dilatancy equation for the mobilized plane in granular material. It was found that the angle of internal friction in granular material is not directly related to the interparticle friction angle (φμ). Instead, it relates to the average interparticle contact angle (θ) on the mobilized plane and the ratio k/f0, representing the degree of the probability distribution of the interparticle contact forces that is biased toward the positive zone of the contact angle θ (along the shear direction), where k is the slope of the linear distribution of the average interparticle contact forces against the interparticle contact angle; and f0 is the average interparticle contact force.

This paper presents a numerical method to simulate the collapse behaviours of unsaturated soils by distinct element method (DEM). The influence of suction in unsaturated soil is reproduced in DEM simulation by introducing an interparticle adhesive force that acts perpendicular to the tangential plane at contact point. A biaxial compression test on an assembly of circular rigid particles is numerically simulated using DEM by incorporating interparticle adhesive forces. The collapse behaviours of unsaturated soils during isotropic compression and biaxial shear are simulated by means of releasing the interparticle adhesive forces from the initially incorporated values to zero at constant stress state. The numerically simulated results are then compared with the results of triaxial compression tests on unsaturated compacted clays and qualitative similarities are obtained. The influences of the mean stress, the stress ratio and the interparticle adhesive force on the collapse behaviours are numerically investigated. The fabric structure and the particle stability of the simulated specimen before and after collapse are also investigated and discussed.

建议了一个非线性弹性剪胀K-G模型，即通过变换应力法将SMP破坏准则简单地引入切线剪切模量Gt中，使其能反映中主应力σ2对土体变形强度的影响, 并通过在切线体积模量Kt中耦合一个反映剪切过程的系数的方法来考虑土的剪胀性。用该模型较好地预测了粘土、砂土的三轴压缩、三轴伸长与平面应变试验结果，并用其进行了挡墙土压力的有限元分析计算, 计算结果与模型试验结果基本吻合。

The main dam at the upper reservoir of Tianhuanping pumped storage power station is a rockfill dam with an asphalt concrete impervious lining on the upstream face. It is constructed on a non-homogeneous fully weathered rock foundation. In this paper, we present the case study on the treatment for this non-homogeneous fully weathered rock dam foundation. The treatment includes the partial excavation of the fully weathered rock in different depths with respect to the dam deformation, and the enlargement of the transition curvature at the junctions of the inclined dam face and the reservoir floor, as well as the reinforcement for the asphalt concrete impervious lining with a layer of polyester mesh at the parts where tensile strains of the lining are large. A three-dimensional (3D) finite element analysis is carried out for the main dam to provide the basis for the proposed compound treatment method. To account for the effect of the intermediate principal stressσ2 on the deformation and strength of soils, a simple constitutive soil model is proposed for the finite element (FE) analysis. So far, this project has operated well for more than 5 years without any maintenance for the main dam’s asphalt concrete impervious lining, illustrating the success of the treatment for the fully weathered rock dam foundation.

An in-situ direct shear test apparatus, in both small and large sizes, and its testing techniques have been developed. This test is performed simply by pulling horizontally a latticed shearing frame, embedded in the ground, with a flexible rope or chain under the application of a constant vertical load on the sample. In the new test, the real normal and shear stresses acting on the shear plane can be exactly measured. A number of the large-sized in-situ direct shear tests have been performed on eight kinds of coarse-grained granular materials including rockfills at different construction sites of embankments. The measured shear strengths approximate those of large-sized triaxial compression tests on samples with parallel grain-size distributions. The smaller version of this new test has been used successfully for testing sands and clays. For clays, artificially produced or in-situ, the measured undrained shear strengths are nearly equal to qu/2 by unconfined compression tests on the same clays. The extreme simplicity and high accuracy of this newly developed test are emphasized.