Experimental Study On Erosion Of Loessial Subsandy Soil Under Low Pressure Seepage

Jilin Qian'an mud-Forest National Geopark is located in Qian'an County of Jilin Province,Songyuan City.It was approved as a National Geopark in 2009.However,in recent years,the impact of surface sub-erosion and groundwater sub-erosion has resulted in a large reduction in the landscape of the mud-forest and collapses disaster caused by sub-erosion,moreover the key to solve this problem is the further study about the mechanism of the sub-erosion of mud-forest.At the development area in the mud-forest,it is more common that the phenomenon of sub-erosion blank and disintegration of the mud-forest soil under low pressure seepage,thus it's necessary to carry out the corresponding study to the excitation conditions and sub-erosion rate for evaluating the development speed of the mud-forest provides the basis.This paper,based on the special engineering geological properties of the loessial subsandy soil in the mud-forest,combined with the National Natural Science Foundation Project "The study of the influence mechanism of the engineering geological characteristics of the Qian'an mud-forest soil on the mud-forest sub-erosion ".Analyzing the factors influencing the occurrence and development of sub-erosion from aspects of soil particle size composition,soluble salt composition and disintegration,on the basis of the field investigation of landform types and failure characteristics of mud-forest.Aiming at the sub-erosion of low pressure seepage in mud-forest area,the erosion rate and critical hydraulic gradient of loessial subsandy soil under low pressure seepage are studied by self-made erosion simulation device.It is provided scientific basis for the sub-erosion development condition and speed of the mud-forest,furthermore preventing and controlling of the sub-erosion disaster in Qian'an.The main results are as follows:(1)The sub-erosion phenomenon and development of the mud-forest Geopark were investigated.Moreover the related geological,hydrologic and meteorological data were collected.The types of the sub-erosion landforms were investigated in the field,finally the failure characteristics were preliminarily analyzed.(2)The mud-forest soil is mainly powder grain,high porosity,the surface of soil is leached,and the soluble salt has high content,which is easy to be corroded by groundwater.By taking the slaking test,the characteristics of the easy disintegration of the mud-forest soil in water are analyzed.(3)A mechanical sub-erosion device can be made to simulate the process of mechanical sub-erosion under low pressure seepage.The influence of density and hydraulic gradient on the development process of the sub-erosion is simulated by the mechanical sub-erosion device.The critical hydraulic gradient of mechanical erosion is determined.The mechanical sub-erosion device has also determined total soluble salt content,erosion rate and current velocity with time under different density and hydraulic conditions.