Mesomechanical simulation of direct shear test on outwash deposits with granular discrete element method

The mechanical properties of outwash deposits which are taken as unconsolidated geo-materials with the characteristics of non-uniformity, heterogeneity and multiphase have attracted much attention in engineering. According to the results of laboratory direct shear test on the remolded samples, the soil particle parameters of numerical model based on in-situ particle size cumulative curves and 3D granular discrete element method were determined. Then, numerical experiments on different lithology, stone content and gradation composition were conducted. The results show that it is not a flat surface but a shear band that yields in the sample. The curve of particle velocity vs distance from the designed shear surface of test model that is taken as a datum plane in the vertical section of sample shows in "S" shape. The shear disturbance area is about twice the maximum diameter of stone blocks. The greater the stiffness of stone is, the rougher the shear surface is. The shear strength of outwash deposits is largely controlled by lithology and stone content, and the bite force between stone blocks is the root reason of larger friction angle. It is also shown that strain hardening and low shear dilatancy occur under high confining pressure as well as possibility of shear shrinkage. But it is easy to behave shear dilatation and strain softening under low confining pressure. The relationship between particle frictional coefficient and stone content presents an approximately quadratic parabola increase. The strain energy first increases and then drops with the increase of frictional energy. The cohesion increases with soil stiffness increasing but decreases with stone stiffness increasing. Numerical results are consistent with the laboratory test results of remolded samples, which indicate that this method can be a beneficial supplement to determine the parameters of engineering deposit bodies.

Study on the mechanical properties of outwash deposits with random structure method

Outwash deposit is one of the major threats to the safety and stability of railway transit engineering in the Sichuan–Tibet area.In this paper,different samples of outwash deposits were prepared based on the random structure method,and a series of large-scale direct shear tests were carried out under different normal stresses.The influence of stone content and the spatial distribution of stone blocks on the physical and mechanical properties of outwash deposits were studied.The results show that with the increase of stone content,the shear stress-displacement curve changs from strain softening to strain hardening.The shear zone is larger,and its shape is more tortuous due to the movement and rotation of stone blocks.The internal frictional angle increases linearly while the cohesion diseases with the increase of stone content.The main influence of the spatial distribution of stone blocks on the mechanical properties of outwash deposits is the peak stress.The shear zone is mainly determined by the distribution of the stone blocks near the shear zone.