# Research on Mechanical Behavior of Geogrid-Soil Interface Under Rainfall Infiltration
## 1 Introduction
The widespread use of reinforcement in engineering practice has shown that they are essential for improving the soil properties under actual working conditions. The effect of rainfall on soil is mainly reflected in the change in moisture content. Therefore, an in-depth study of soil moisture content is important for soil prevention and control under rainfall. [PERSON] et al. [21] found that an increase in soil moisture content can significantly reduce the shear strength of the reinforced soil interface. [PERSON] et al. [22] studied the interface characteristics of building demolition waste as a filler material for reinforced structures. It was found that the interfacial shear strength between it and geosynthetics after proper compaction was affected by water content, and high-water content would lead to a decrease in strength. [PERSON] et al. [23] studied the interfacial shear strength of five geosynthetics in marginal clay sand under different water contents through large-scale direct shear tests. The results show that compared with the optimal water content, the cohesion and internal friction angle decrease significantly when the water content increases by 6%. [PERSON] et al. [24] found that the interfacial friction angle and friction force of the specimens increased with decreasing moisture content by using the direct shear test and pullout test, respectively. The results of the studies show that the moisture content of soil has a significant effect on its shear strength, and with the increase in the moisture content, the cohesion and internal friction angle decrease. However, most of the above studies focused on the strength performance of soil under fixed moisture content, and there is a lack of studies on the dynamic change in moisture content. It is not known whether the change trend of cohesion and internal friction angle under rainfall infiltration conditions is consistent with the existing conclusions. At the same time, most of the current studies focus on the influence of a single factor on the mechanical behavior of the reinforced soil interface. However, in practical engineering, the reinforced soil structure is often in a complex multi-factor coupling environment. This raises the question of how to accurately analyze the effect of rainwater infiltration on the shear strength of soil during rainfall. In order to more realistically simulate the effect of rainfall infiltration on soil properties, this paper simulates natural rainfall through a series of large indoor direct shear tests, monitors the change in soil moisture content in real time, investigates the moisture content at different time points and different soil depths, analyzes the shear strength of soil under dynamic moisture content, and explores the interaction mechanism of the geogrid-soil interface under rainfall infiltration, so as to provide a more accurate theoretical basis and practical guidance for slope stability evaluation and reinforced soil structure design under the change in the moisture content of soil in practical engineering, and promote the development of this field to be more in line with the actual working conditions.