# Research on Mechanical Behavior of Geogrid-Soil Interface Under Rainfall Infiltration
## 4 Conclusions  
In this paper, direct shear tests were employed to investigate the interface shear characteristics of geogrid-sand under varying normal stresses, shear rates, and infiltration times, leading to the following key conclusions. * The normal stress exerts a substantial influence on the shear strength of the geogrid-soil interface, with the shear strength increasing as the normal stress rises. Even in the presence of rainfall infiltration, the soil's behavior adheres to the Mohr-Coulomb criterion. Consequently, in practical engineering applications, the normal stress at critical locations can be augmented by rationally adjusting the structural configuration or applying external loads. For instance, in the design of the slope of a dam, a suitable increase in the weight at the top of the slope can enhance the normal stress within the soil of the dam slope, thereby improving its shear strength. For the soil affected by rainfall infiltration, careful attention should be paid to the alterations in soil parameters induced by rainfall, and the increased amount of normal stress should be calculated judiciously. In regions with frequent rainfall, a certain safety margin should be reserved and the increased value of normal stress in the design should be appropriately enhanced. * The impact of shear rates on the shear stress-shear displacement curve of the unreinforced sand is not pronounced, and the variations in shear strengths and shear strength indicators with respect to the shear rates are relatively minor. In contrast, compared to the unreinforced sand, the effect of shear rates on the geogrid reinforced sand is more conspicuous, with its peak shear stresses decreasing as the shear rates increase. Therefore, during the design of structural reinforcement, it is essential to anticipate the potential shear rate scenarios that may occur. For areas where high shear rates are likely to manifest (such as regions where the bottom of the slope is scoured by water flow or near the flood discharge outlet of the dam), reinforcement measures with enhanced resistance to high shear rates should be implemented. For example, selecting geogrid types with superior shear resistance performance and optimizing their laying patterns can mitigate the risk of peak shear stress reduction under high shear rates. In unreinforced sand areas, although the influence of the shear rate is not prominent, considering that long-term rainfall may lead to alterations in the properties of local soil, appropriate attention should still be paid. For example, incorporating drainage facilities into the design can reduce the accumulation of rainwater in the sand and lower the potential shear failure risk associated with the increased moisture content. * Under the influence of rainfall infiltration, the moisture content of the soil undergoes dynamic changes, gradually increasing with the prolongation of infiltration time. Owing to the constraints of the test conditions and apparatus, the final moisture content tends to stabilize. The increase in moisture content leads to a decline in the peak shear stress at the geogrid-soil interface, accompanied by a reduction in both the friction angle and cohesion. Hence, when designing the drainage system, it is crucial to ensure efficient rainwater drainage to control the soil moisture content. For example, installing multiple layers of drainage pipes in slopes and dams, and rationally designing the spacing and diameter of the pipes can be based on the predicted rainfall intensity, and the soil permeability coefficients can maintain the moisture content of the soil at a relatively low level as much as possible, thereby minimizing the reduction in peak shear stress, friction angle, and cohesion caused by increased moisture content. Additionally, measures such as waterproof cover layers can be considered to curtail rainwater infiltration and thus limit the increase in the soil moisture content.