Experimental Study On Horizontal Seepage Failure Characteristics Of Gap-graded Goarse-grained Soils Under Stress And Lateral Restraint

Earth rock dams play an important role on the national economy and the construction of infrastructure.Since current knowledge on the design and construction of earth rock dams is still quite limited,earth dam failures have occurred frequently in our country,of which the seepage failure of soil is the main reason.In addition,along with the construction of high-rise buildings in China's major cities in recent years,the seepage stability of groundwater in deep foundation pit project has become a difficult problem in engineering construction.Therefore,in order to provide a reasonable basis for the seepage control in engineering construction,it is very urgent to find out the mechanism of the seepage failure.In the practical engineering,the seepage direction of the soil of the earth rock dam and the foundation pit is closer to the gravity direction of soil,but the current indoor seepage failure tests are often based on vertical seepage without considering the influence of the flow direction,and do not take into account the stress state of the soil,leading to the inconsistency of test results and the practical test results.In order to reduce the gap between the test conditions and the practical engineering conditions as much as possible,we develop a new permeability experimental apparatus,which can better simulate the situation of filling and flow pattern in the cushion layer of the real dam.In addition,the vertical stress state of the soil is taken into account in the test.Then,the test apparatus is used to conduct seepage failure test in order to study the effects of vertical stress,compactness and fine particle content on the horizontal seepage failure characteristics of gap-graded goarse-grained soils under confining stress.Experimental results show that the vertical stress,dry density and fine particle content have significant influence on the seepage failure characteristics of soil samples.Firstly,when the fine particles are filled with the coarse particle pores,the additional stress of the fine particles moving in the horizontal direction comes directly from the transmission of the vertical stress,and the greater the vertical stress,the greater the binding force of the fin e particles.so with the same fine particle content and initial dry density,both critical hydraulic gradient and failure hydraulic gradient increase with the vertical stress.In the horizontal penetration test,the horizontal pore channels have been compr essed by the vertical stress during the development of the seepage,and the horizontal pore channels will not be extended by the loss of fine particles,so permeability shows multiple cycle process of increase and decrease.Besides,both the initial permeability coefficients and the maximum permeability coefficient s decrease with the increase of the vertical stress,and vertical stress is conducive to seepage control.The erosion rate of fine particles also decreases with the increase of vertical stress.Secondly,with the same vertical stress and the same dry density,the critical hydraulic gradient and failure hydraulic gradient increase with fine particle content,because porosity is smaller and the particles are compressed more closely.Besides the initial permeability coefficient,the maximum permeability coefficient and the erosion rate of fine particles decrease as the fine particle contents increase.When fine particles are incompletely filled with coarse particle pore,the initial permeability is the largest.Finally,with the same vertical stress and the same fine particle content,both critical hydraulic gradient and failure hydraulic gradient increase with the dry density of the soil samples,because the fine particles have a larger filling de gree of the coarse particle pores and a smaller effective diameter of the pore channels,and when the fine particles are filled with the coarse grain pores,the vertical stress is transferred between the fine particles so that the horizontal migration of t he fine particles becomes more difficult.In addition to the initial permeability coefficient,the maximum permeability coefficient and the erosion rate of fine particles decrease as the dry density increases.