粒状介质三维复杂应力加载离散元数值试验方法

实际荷载条件下（如交通、地震荷载），粒状岩土材料常受到三维复杂应力路径作用。目前，多数粒状岩土材料的本构理论和模型都基于简单应力路径加载条件下的物理试验提出，在更加复杂应力路径下的适用性则需要进一步验证。但受机械控制的限制，物理试验中无法实现很多客观存在的三维复杂应力路径加载。为了能够再现并分析三维复杂应力路径下粒状介质的力学响应，提出了一种离散元数值试验方法，该方法采用球形数值试样，通过直接控制试样边界应力达到对3个主应力大小和方向的任意控制，从而可以实现诸多物理试验中无法实现的复杂应力路径。通过与目前常见的一些物理试验进行定性对比，论证了该数值试验方法通过高精度的加载控制和测量能够再现已有物理试验现象。在此基础上，进一步开展了应力主轴的三维旋转，分析了在这种实际存在却无法通过物理试验再现的加载条件下粒状介质的变形规律，初步显示了提出的数值试验方法在深入研究三维复杂应力路径下粒状介质力学响应方面所拥有的能力和优势。

DEM numerical test method for granular matter under complex 3D loading

Under engineering loads such as traffic and seismic loads, granular soil is often subjected to complex 3D stress paths. Most existing constitutive theories and models for granular soil have been proposed based on results from laboratory tests conducted under relatively simple loading conditions. Therefore, the existing constitutive theories and models need to be verified under more realistic stress paths if they are to be applied to engineering practice. However, due to limitations in mechanical control, conducting laboratory tests with complex 3D loading is often very difficult or even impossible. In this study, a new numerical test method is proposed to provide the means to investigate the mechanical response of granular material under complex 3D loading. Spherical numerical specimens are adopted along with high precision stress-controlled boundaries, allowing for the application of any arbitrary stress state, forming the basis for complex 3D loading. Combined with a set of stress and strain measurement techniques, most existing physical tests can be quantitatively and numerically reproduced. Then, the 3D rotation of principal stress axes is achieved, exhibiting the advantages to use this method in the investigation of the mechanical response of granular material under complex 3D loading.