# Discrete Element Simple Shear Test Considering Particle Shape
## 1 Introduction  
The deformation of soil under the action of heap load can be studied with the one-dimensional compression test and conventional triaxial compression test. The direction of stress is fixed during the deformation process. In practical engineering, there is another form of load that can also cause plastic deformation. Different from the previous form of load, its stress direction changes in the process of soil deformation, such as in foundation pit excavation, dam construction, and wave load traffic load. The stress direction inside the soil is rotating, which will lead to noncoaxial plastic deformation [1] and will impact the stress-strain [2]. In laboratory tests, the simple shear test is often employed to investigate the stress-strain characteristics of soil under the condition of principal stress axes rotation. Swedish Geotechnical Institute first invented a simple shear apparatus [3], and many researchers have carried out extensive laboratory tests. [PERSON] [4] investigated the effect of frequency and vertical stress on cyclic degradation in clay via a simple shear test. [PERSON] [5] showed the difference in stress and strain rate directions in a simple shear test with aluminum rod deposits. [PERSON]'s [6] simple shear test reveals that noncoaxiality causes the dilatancy curve to depart from the Rowe line under the principal stress axes rotation in a simple shear test. In the hollow cylinder torsional shear test, [PERSON] [7] came to similar conclusions. The stress-strain can be measured in the laboratory test, but the micro-characteristics of geomaterials cannot be captured, such as the fabric of geomaterials, the contact force of particles, and the anisotropic parameter [8]. The limitations of laboratory tests are also reflected in the microscopic design of granular materials; although some ideal granular materials were used for testing [5], factors such as particle shape and deposition angle cannot be fully considered because of the high cost. This is also unfavorable to the development of the constitutive model. In theory study, the noncoaxiality has integrated into the constitutive model based on the laboratory tests [9, 10]. This method seems to belong to image fitting, and several researchers have developed the constitutive model that considers the micro-characteristics of geomaterials [11], but some microscopic parameterscannot be directly obtained from laboratory tests, and are generally derived from previous experience [12]. The discrete element method (DEM) is based on contact mechanics to model individual particles that can capture macro and micro variables and design particle morphology, it is widely used in simulated soil mechanics tests. [PERSON] [13] investigated granular materials' strength and microscopic mechanisms subjected to true triaxial stress paths. [PERSON] [14] investigated the micromechanical behavior of granular materials under rotating shear stress. Under conditions of principal stress axes rotation, [PERSON] [15] simulated the formation of the shear band and illustrated the evolution of noncoaxiality via the simple shear test. [PERSON] [16] employed finite element and discrete element methods to simulate the simple shear test and biaxial test of granular materials and validated the constitutive model's advantage in explaining the behavior of microscale materials. In discrete element simulation, the contact force chain and particle orientation can be captured, and the fabric of contact and particle arrangement can be history [17; 18]. Due to the convenience of discrete element software, the effect of loading rate has been investigated from a microscopic perspective [19]. For different materials, the effect of loading rate on the stress-strain of materials is different [20; 21; 22]. From the perspective of discrete element simulation, the force inside the sample is transferred through contact.