| Landslide dam is one of the main types of barrier dams with loose structure and poor stability.Once seepage damage occurs,it will seriously threaten the lives and properties of downstream people.Compared with the artificial earth-rock dam,its material composition is extremely nonuniform,it is in a natural deposition state and there is no special filter material.The possibility of seepage failure is greater.This paper was funded by the National Natural Science Foundation of China project "Experimental Study on Failure Mechanism of Landslide Dams under Coupling of Seepage and Stress"(Number 41977239).Based on the deposition characteristics of the landslide dam,the influence of the nonuniformity on the seepage failure of the dam material and the landslide dam was studied.The main works are as follows.For the Xinmo and Lijiawan landslide dams,the gradation of the dam material was obtained with area sampling-area frequency method and sieving method.Base on the investigation of typical landslide dams,the material gradation and deposition form used in the model test were determined.A series of soil tests were carried out on the dam material obtained from the field,and the soil classification,dry density and specific gravity of the dam material were determined.The horizontal permeability coefficient,initial gradient and failure gradient of each group of dam soils were obtained by using an annular-radial permeameter.The effect of gradation on the permeability of dam materials was discussed.The test results shows that the seepage failure type of the dam material is piping.The test results are compared with the calculated value of the existing critical gradient formula,and the critical gradient formula for the landslide dam material is obtained.The contact erosion tests between dam material and strong or weakly permeable soil were carried out to analyze the influence of horizontal and vertical contact modes on seepage failure.The permeability tests for landslide dam soils considering the nonuniformity were carried out by using the vertical permeameter.The influence of the length and location of the weakly permeable zone on the seepage failure was analyzed.The model tests of a landslide dam with a strong permeability zone inside were carried out.The position and gradation of the strong permeability zone were varied to investigate their influence on the seepage failure of the landslide dam.The failure phenomenon of the downstream slope of the dam,pore water pressure at different locations,seepage discharge and turbidity were observed.Particle composition of the dam soils at different positions after failure was analyzed.The results showed that when the central of dam bottom contained a strong permeability zone,the failure mode were piping and dam surface cracking.When there was a strong permeability zone in the middle of the dam,a composite failure of piping and slope erosion would occur.When the middle of the dam contained a relatively coarse and strong permeability zone,the failure mode were piping,slope erosion and slope collapse.And for this case,the slope dam surface damage was the most serious,the loss of fine particles at the slope foot was more,and the turbidity and discharge peaks were the largest. |
