Study On Water-air Migration Of Loess Aeration Zone Under The Influence Of Cracks And Paleosols

Loess is widely distributed in China and plays an important role in people's production and life.With a variety of irrational human activity(such as excessive irrigation,etc.)increased dramatically,the engineering geological environment in Loess Plateau is becoming more and more fragile.A large amount of farmland irrigation in Jingyang,Shaanxi Province,caused changes in the hydrogeological conditions of loess and frequent occurrence of loess landslides.This paper summarizes and analyzes the previous research results,takes loess in landslide area of the southern Jingyang plateau,Shaanxi Province as the research object,simulates the cracks and paleosols,and uses soil box to carry out the infiltration test of discontinuous irrigation under closed and open strips.From three aspects of wetting front,water content and gas pressure difference,this paper specifically analyzes the water-air migration law of loess aeration zone under the influence of cracks and paleosols,so as to understand the role of water and gas in the development of landslide.The specific research work and main conclusions are as follows:1.In this paper,according to the purpose and requirements of the test,a soil box test device was designed to give an experimental solution to the simulation of indoor cracks and paleosols and the control of gas boundary conditions.The experimental phenomena and data show that the design of the test scheme is reasonable,and the overall test is well completed,which basically reflects the migration law of water-air affected by cracks and paleosols.2.The speed of propulsion of the wetting front under intermittent irrigation is cyclically propulsive.In an irrigation cycle,the propulsion speed of the wetting front is the highest at the beginning of irrigation.With the increase of water migration depth and the decrease of surface soil water,the advancing velocity of wetting front decreases.The cracks in the soil accelerate the migration of the wetting front and the paleosols hinder the migration of the wetting front.3.In the process of discontinuous irrigation,the water content of surface soil regularly presents the law of increasing first,then stabilizing and finally decreasing.The process of water infiltration in the soil below 20 cm in depth is unsaturated infiltration,and the overall change trend of water content first increases and then decreases.With the increase of soil depth,the time when the water content began to change and reach the maximum value gradually increased.After multiple irrigations,the water content was basically stable when the infiltration rate and the recharge strength were balanced.4.The cracks in loess form preferential passage and accelerate the infiltration of water.The water content of the soil in the area affected by the crack is relatively larger than that in the non-cracked area,and the water is obviously concentrated around the crack.As the distance from the crack increases,the soil water content gradually decreases.The soil around the cracks is obviously damaged due to the structure,and the water holding capacity is weakened.After the water is filled,the water recedes and the water content around the cracks decreases.The paleosol in loess seriously obstructs the infiltration of water and forms the perched water over paleosol.When cracks penetrate the palaeosol,the water is introduced into the soil beneath the cracks.At the end of irrigation,the moisture content of the soil near the crack area above the paleosol decreased obviously.5.In intermittent irrigation,the pressure difference of soil in the closed condition increases first and then decreases.Under open condition,the gas discharge in the soil under the open condition is smooth and the pressure difference changes little.With the increase of soil depth,the differential pressure response time lags behind,the pressure difference decreases,and the pressure release rate is faster.After multiple irrigations,the soil saturation increases,and the differential pressure increase value is small,and the change is not obvious.6.Under closed conditions,the gas has a significant effect on moisture migration and moisture content.With the increase of air pressure,the greater the resistance of the gas to moisture migration,the higher the water content of the soil.The existence of paleosol impedes the movement of gas,which causes the gas in the soil to compress,and the pressure difference increases.The presence of cracks forms an exhaust passage,which causes the gas in the soil to diffuse and the pressure difference to decrease.