Numerical investigation of the influence of non-uniform factors on the monotonic/cyclic behaviour of coarse-grained soil

Coarse-grained soil (CGS) has been extensively used in engineering practices because of their advantages of relatively high strength, easy compaction and small deformation. In engineering design, CGS is usually regarded as a non-liquefiable soil. However, many post-earthquake surveys have shown that CGS, such as sandy gravel, can be seriously liquefied, meaning that under certain seismic loads, CGS with loose to moderate densities might have the potential to be liquefied. In this study, soil-water coupling finite difference-finite element (FD-FE) deformation analyses, based on the cyclic mobility (CM) model, were conducted to investigate the monotonic and cyclic characteristics of CGS. The model can accurately describe the complicated mechanical behaviour of CGS, considering the influences of the stress-induced anisotropy, the density and the naturally deposited structure of soils in a unified way. The material parameters of CGS were calibrated by large-scale triaxial tests. Particularly, the influences of non-uniform factors on the element behaviour of CGS subjected to monotonic/cyclic loading were systematically studied, such as the gravitational stress field (GSF) of the specimens, the friction between the loading plate and specimen (FLPS), the confining pressure, the cyclic shear stress ratio (CSR), and the loading frequency, etc. It is found that the CM model can reproduce the stress-strain-dilatancy relation of CGS in the CU‾ and CD tests well and that the GSF and FLPS have a certain impact on the element behaviour of CGS. However the average value results from the numerical simulations can quantitatively and qualitatively describe the monotonic/cyclic mechanical behaviour. In addition, under lower confining pressure or higher CSR, the non-uniform distribution of volumetric and axial strain inside the specimen will be prominent, and the specimen enters the cyclic-mobility stage more easily. High loading frequency and CSR will cause a large distortion of the specimen, at which point the element test, strictly speaking, is no longer an element test.