Study On Permeability Of Purple Soil In Chongqing At Saturated And Unsaturated Condition

Purple soil is widely distributed in southwest China,soil horizon shallow.Atmospheric forces(such as weathering,erosion,wetting and drying cycles)and various chemistry and biological effects,the soil is prone to disintegration and alteration,resulting in loose soil structure,which often causes natural disasters such as landslides and soil erosion.Permeability is one of the main hydraulic characteristics of soil,reflects the permeability of soil.It is an important parameter for studying landslides and assessing soil erosion effects.The paper takes Chongqing purple soil as the research object,Simulating different rainfall intensity and soil depth,and factors affecting the permeability of purple soil are analyzed and studied in a more comprehensive way.The main research contents are as follows:First of all,Utilizing multifunction triaxial apparatus,the effects of confining pressure(50,100,150,200,250 k Pa),osmotic pressure(20,30,40,50 k Pa)and axial compression(0,25,50 k Pa)on the permeability of Chongqing purple soil were studied respectively,the results show that:(1)The confining pressure will cause the soil particles to dislocate,rearrange,and compact the soil body,which will have a significant impact on the permeability coefficient.With the increasing of confining pressure,the permeability coefficient of soil decreases rapidly,But when the confining pressure increases to a certain value,the reduction of the soil permeability coefficient decreases and tends to be stable;(2)Osmotic pressure has little effect on the permeability coefficient of purple soil;(3)The increase in the depth of the cover soil increases the axial pressure on the soil,which results in the soil being further compacted and the permeability coefficient of the soil reduced.Considering the coupling effect of confining pressure and axial pressure,when the confining pressure is small,the influence of axial pressure on the decrease of permeability coefficient of purple soil is obvious;when the confining pressure is large,the soil itself is subjected to a certain compaction effect,so that the reduction of the permeability coefficient by the axial pressure is suppressed.Secondly,designs and develops the soil instantaneous permeability tester independently,and directly measured the permeability coefficient and soil water characteristic curve of unsaturated soil.Simulate different rainfall conditions(5mm/h、15mm/h、30mm/h),the curves of infiltration rate,cumulative infiltration,and infiltration peak with time at different rainfall intensities and the changes of volumetric moisture and suction at the monitoring site were obtained;And then studies the hydraulic properties of remodeling Chongqing purple soil under unsaturated conditions,such as permeability and water holding capacity,The results show:(1)When the initial soil moisture content is the same,the rainfall intensity will affect the infiltration rate.The infiltration rate of soil is related to the moisture content.The soil with lower water content has higher infiltration rate.Under different rainfall intensity,the cumulative infiltration volume of soil is different.The greater the rainfall intensity,the greater the cumulative infiltration of water in soil and the greater the cumulative infiltration volume.(2)It can be seen from the time-history curve of volumetric moisture content and the curve of suction over time,under different rainfall intensity,the time for water infiltration to the same monitoring point is different,the greater the rainfall intensity,the faster the water infiltration rate;And the greater the rainfall intensity is,the larger the water content increases to a stable value.(3)Although the rainfall intensity will affect the penetration rate of water in the soil,it will not affect the permeability coefficient and water holding capacity of the purple soil.For unsaturated purple soils,it is found that there is a linear relationship between the volumetric moisture content and the logarithm of the permeability coefficient lgk.The fitted linear equations can provide scientific basis for engineering seepage analysis.The influence of many factors on the permeability characteristics of purple soil was obtained through experiments,which can provide scientific basis for the study of engineering problems such as landslides and soil erosion.