Soil and rock mixture (SRM) is complex geological material that frequently leads to ground collapses, landslides, and debris flows. The mechanical and hydraulic properties of SRM have consistently attracted extensive attention. However, due to the presence of both large and small rock blocks, both experimental investigations and traditional mesh based numerical methods face significant challenges in the accurate evaluation of SRM mechanical properties. The numerical manifold method (NMM) is an excellent choice for this purpose as it effectively overcomes obstacles to mesh generation of complex SRM. Before exploring the hydraulic properties of SRM by NMM, it is necessary to construct a random preserved structure model of SRM, where the rock blocks are randomly distributed in space under a seismic load, which is a primary cause of structural changes in SRM. Using an explicit iterative scheme called the continuous-discontinuous element method (CDEM), we simulated the redistribution of rock blocks in SRM under artificial or natural seismic loads. Finally, we concentrated on determining the influences of some factors on SRM permeability using three-dimensional numerical manifold method (3D-NMM).

Horizontal drains have been widely installed along expansive soil slopes to maintain slope stability. However, these drains typically get clogged with clay particles after several years of operation and must be maintained and replaced regularly. This paper proposes a new type of horizontal drain with a replaceable tubular filter element (RTFE) to overcome the time-consuming nature and laborious replacement procedure of existing horizontal drains. Tests were conducted to compare its drainage performance with that of a conventional horizontal drain. The effects of horizontal drain clogging on the pore water pressure and slope stability were analyzed using the equivalent permeability coefficient of the expansive soil considering the adverse effects of cracks that are randomly distributed in the soil when the matrix suction exceeds the air-entry value. This coefficient was then used as one of the input parameters in the finite element analysis (FEA) for a hydro-mechanical coupling simulation. A replacement standard for the tubular filter element was established according to the numerical results, and the replacement method was explained. The study results showed that the RTFE-equipped horizontal drain was evidently superior to the conventional horizontal drain owing to the advantage of quick replacement. It can also effectively preserve the soil and prevent infiltration deformation caused by the loss of skeleton particles, implying a more economical, effective, and controllable means for the dewatering of expansive soil slopes. This study provides references for the construction and management of engineering projects involving horizontal drainage systems.