Seepage and Erosion Mechanism of Fine Sand with Different Clay Contents During Rising of Groundwater Level

Underground pipeline is an important part of urban function, but in recent years, ground subsidence disaster accidents due to underground pipeline damage and then leakage have occurred repeatedly, which seriously affects and jeopardizes the safety of people's lives and properties. For the research of ground subsidence disaster, the current domestic and international research is still in the initial stage, and the relevant experimental law is relatively small.In order to study the formation process of ground subsidence and the law of occurrence of subsidence disaster, this paper carries out the erosion damage test of unpressurized pipeline breakage and seepage under the condition of rising groundwater. At the same time, for the sandy soil containing clay grains which is common in the project, it carries out the indoor modeling test by using its own self-designed semi-structural test model, and analyzes and researches on the test results. The main contents and results of the research are as follows: Under the condition of rising groundwater level, the erosion damage of seepage of unpressurized pipeline can be divided into three stages: the initial loss stage, the erosion cavity expansion stage and the soil surface collapse expansion stage.Under the condition of rising groundwater level, the erosion degree of fine sandy soil decreases with the increase of clay content. The degree of erosion of fine sandy soil with 10% clay content decreases, but it will form the dormant erosion cavities in the ground. When the clay content increases to 15%, no soil erosion occurs in the test process. Therefore, adding clay to actual non-cohesive fine sand soil can significantly reduce the erosion caused by pipeline leakage in the underground soil. By fitting the relationship between the area of erosion cavities and the clay content of fine sandy soils with different clay content, it is found that the two conform to the S-type Logistic model and have a good goodness of fit.