中文摘要：

砂土是一种典型的颗粒材料，其力学特性和变形机制是细观颗粒在荷载作用下的宏观表现，鉴于砂土具有显著的颗粒性和碎散性，使得对其进行细观颗粒层面的研究非常必要。将土颗粒简化为空间椭球体，假设方向角满足正态分布规律，应用细观统计的方法，从颗粒层面对砂土的摩擦特性和破坏机制进行研究。砂土剪切面上的摩擦特性主要是颗粒在剪切荷载作用下，克服垂直于剪切面应力抬升所遇到的阻力。颗粒运动方向与剪切面滑移方向的夹角可视为单个颗粒的摩擦角，颗粒摩擦角满足与方向角同样的正态分布规律；砂土的剪切破坏是颗粒重排列和应力重分布的过程，该过程中一部分颗粒摩擦角不断弱化，而承载颗粒数量逐渐增多，土体内部应力分布渐趋均匀；随着垂直于剪切面荷载的增大，砂土内摩擦角随之弱化神小．内鹰熔角与荇曹夕问且右对商羊磊．百T讲行骨仙计笪．

英文摘要：

Sand is a kind of typical granular material. Its mechanical and deformation characteristics are macro phenomenons of its meso-particles under loading. In view of the sand with graininess and fragmentation, the meso-structure level research on sand is necessary. In this research, the soil particles are simplified as ellipsoids. The direction angles of the soil particles obey normal distribution. The friction characteristics and failure mechanism of sand material are studied at meso-partieles level based on meso-statistics. The friction characteristic of sand is composed of the resistance caused by the rise of the sand particles around the plane which is normal to the shear plane. The angle between the particle movement direction and the shear plane is considered as the friction angle of a single particle. The friction angle and direction angle meet the same normal distribution law. The shear failure process of sand composes of particle rearrangement and internal stress redistribution. During this process, some particles friction angles gradually become weak and the number of particles sustaining load increases. Moreover, the distribution of sand internal stress gradually become uniform. With the increases of the vertical load, the internal friction angle of the sand decreases. The relationship between the internal friction angle and the applied load can be therefore quantitative calculated.