Experimental Study On The Seepage Characteristics Of Unsaturated Loess

Soil is a three-phase system composed of particles,water and air.Water content directly affects the properties of soil.Especially for collapsible loess which is widely distributed in northwest China,seepage will cause significant subsidence of soil and even damage to the structures on it.Therefore,in the engineering construction,to prevent water from seepage in the foundation soil and adopt waterproof measures is an important means to ensure the engineering quality.To prevent water from immersing in soil,the seepage rate and the law of seepage path of soil should be studied and mastered firstly.This paper mainly carried out the following research work:(1)Through the indoor model test,soil permeability characteristics such as vertical and horizontal seepage rate and soil-water characteristic curve of soil samples were obtained,and the influence of soil particles' migration with seepage on the seepage law was analyzed through the micro-structure test of soil.(2)Using the TDR-3 soil moisture meter to monitor the development law of the seepage path of soil after in-situ pit seepage;(3)Analyze the indoor and in-situ pit seepage test results,and discuss the seepage rate and seepage path law of loess.The results show that :(1)The seepage rate of unsaturated loess soil varies in both horizontal and vertical directions,and develops with power function.However,vertical seepage is greatly affected by head pressure and gravity,while horizontal seepage is mainly affected by matric suction.(2)According to the microscopic structure of the soil,the particles migrate along with the direction of seepage,resulting in the gradual increase in the density at the end of seepage and the decrease in the percentage of pore area.After seepage,the dry density at end of the seepage is about 1.07 times that of the previous seepage segment.(3)The monitoring results of in-situ pit seepage test show that the horizontal diffusion distance increases first and then decreases when soil begins to seepage,and the maximum vertical seepage depth is about 10 times of the horizontal seepage maximum distance.The horizontal seepage path first diffuses outward and then converges inward from the point of convergence.(4)With the development of seepage,the seepage energy is lost,the seepage resistance is gradually increased,and the soil matric suction is weakened,resulting in the convergence of the soil seepage diffusion profile at a deeper position.(5)The permeability characteristics of unsaturated loess were studied from laboratory test and in-situ pit seepage test.,providing a reference for the waterproof design of foundation at loess.