直接剪力試驗為常見的實驗室試驗之一，用來獲得土壤的工程性質，尤其對於乾燥的粒狀土壤；本研究中，用描述顆粒間力與位移關係的微觀參數來對應顆粒堆整體的宏觀工程性質；可以發現顆粒對整體的宏觀摩擦角與微觀參數的接觸勁度、剪切勁度以及顆粒基本摩擦角有關。於離散元素法的模型內也發現到顆粒堆的膨脹，基本上整個試體的膨脹來自於剪動帶顆粒的膨脹。此外，觀察延固定破壞面而產生的不均勻應力狀態；隨著正向應力的增加，位於既定剪動面中間的應力狀態會變得比較單純，呈現純壓縮載重狀態；而在較小的正向應力下，應力的狀態呈現壓縮載重以及伸張載重的組合。應力路徑的變化，某種程度上說明了直接剪力試驗結果總會高估材料強度的原因，應力路徑以壓縮載重狀態為主，而壓縮載重試驗下所得到的材料強度本來就會比其他試驗結果強度來的高一些。Direct shear test has been among common laboratory tests to obtain the engineering properties of soils, especially for dry granular soils. In this study, the microscopic parameters to describe the force-displacement relationship between particles are compared to the macroscopic engineering properties of the particle assemblies. It was found that the friction angle of the particle assembly is related to the contact normal and shear stiffness and the particle friction from a microscopic point of view. Dilation of the particle assembly is also observed in the discrete element model. Basically the dilation of the overall particle assembly comes from the dilation of the particles in the shear zone. Furthermore, the non-uniformity of stress states along the predetermined failure plane is examined. As the normal stress increases, the stress state in the middle of the predetermined shear plane also becomes less complicated with pure compression loading, while for the smaller normal stress, the stress states are combinations of compression and extension loading. The variations of stress path somehow also explains why a direct shear test can overestimate the strength of a granular material, since a compression loading test can yield the highest strength comparing to other test types.
