1. Introduction
Rainfall is one of the main causes of instability and failure of roadbed and other projects. After rainfall, surface runoff is formed on the road, and some of rainwater by the drainage system flows on both sides of the road, and part of rain water through the cracks of pavement structural the roadbed. On the one hand, it leads to the soil mass increases, and the original stress state in the soil of subgrade is changed, the shear strength of the soil is weakened, and the shear stress is increased; on the other hand, the effect of seepage in the soil can also promote this phenomenon. Retaining wall is one of the commonly used supporting structures in subgrade engineering. It is very necessary to analyze the strength of the back of the subgrade retaining wall to ensure the stability and durability of the roadbed. Earth pressure is one of the main loads. Drainage system is usually arranged in the de