Laboratory tests on development of seepage failure of overlying layer during piping of two-stratum dike foundation

The piping erosion process in two-stratum dike foundation is simulated by means of laboratory tests to study the influence on the overlying clay layer after piping of the dike foundation. Through the macroscopic observation, camera auxiliary shooting and change of piezometric level, flow rate and sand production during the tests, the occurrence of damage and developing process of clay layer under the rigid plate are analyzed. After piping, the fine sand particles on the top are gradually eroded, and a concentrated leakage passage gradually developing upstream is formed. Due to the gap between the leakage passage and the clay layer, slight settlement and flows lead to inhomogeneous deformation in the clay layer, so cracks are produced and become larger and larger under the action of hydraulic fracturing. So water rapidly flows between the collapsed clay and the cover through the crack. Under this effect, the clay layer is scoured and the range of damage develops upstream with the piping. The destruction of the clay layer promotes the occurrence of piping, and the piping passage continuously developing upstream also accelerates the destruction of the clay layer. Two kinds of processes are interactive.