Numerical investigation into the formation of pipe flow and the influencing factors in soil-rock mixtures

Soil-rock mixture (S-RM) slopes are widely distributed in mountainous regions, and the occurrence of landslides poses threats to residents and the economy. Hence, it is of great importance to investigate the stability of the S-RM slope. The existence of a pipe drainage system plays a key role in the assessment of slope stability. This work investigates the formation and development of a pipe drainage system in the S-RM during the seepage process. A new numerical approach based on a characteristic geometric model of the S-RM and a multi-physical field finite element coupling model of seepage-erosion-stress is developed, which is further validated by the experimental results. Moreover, the effects of the initial porosity distribution, volumetric block proportion (VBP), and hydraulic gradient on the development of drainage systems are further studied. The results show that the formation of the seepage channel is influenced by both the initial porosity and rock distribution in S-RM. The drainage channels are generated preferentially in the zone with higher initial porosity and the zone where the seepage direction is not blocked by rocks. With the increase of VBP, both the number and width of the drainage channels decrease. A higher hydraulic gradient can improve the formation of the seepage channels in terms of the number of channels as well as the width of channels. This work enhances the understanding of the evolution of pipe drainage systems in S-RM and provides further insights into the potential control measures in landslide treatments.