Study On The Disintegration And Collapsibility Of Loess Of Gully Land Consolidation Under Eluviation In Yan'an Area

Loess Plateau is the loess region with the largest continuous loess distribution area and the thickest soil layer in the world.It is also a region with fragile ecological environment and high incidence of geological disasters in China.These geological disasters severely restrict the development of society and economic in the loess area.In order to solve the constraints of the regional environment on social development,Yan'an city has carried out large-scale cutting hills to bulid cities and gully land consolidation,which has expanded urban development space and provided development opportunities for local social economy.However,the large number of excavated and filled loess slopes formed by the cutting hills to bulid cities and gully land consolidation have serious slope erosion and gully soil collapsibility under the action of rainfall,which is closely related to the disintegration and collapsibility of loess under eluviation.Therefore,it has very important practical and theoretical significance to carry out research on the disintegration and collapsibility of the gully land consolidation loess in Yan'an city.This paper takes Yan'an Nangou gully land consolidation engineering as the research background,based on the field investigation,sampling and data processing,which carried out eluviation tests on Q₃undisturbed loess in Yan'an Nangou under different eluviation conditions,and then carried out indoor collapsibility and disintegration test on the eluviated soil samples,combined with SEM test and grey correlation analysis,the influence of eluviation on disintegration and collapsibility of Q₃ undisturbed loess in Yan'an Nangou was studied.The main results and conclusions are as follows:(1)Based on particle size analysis and X-ray test,the particle size and mineral composition of Yan'an Nangou Q₃undisturbed loess were obtained.Loess particles are mainly powder particles,the main clastic and clay mineral is the quartz and chlorite.Based on the analysis of water quality in eluviation test,the concentration of Na⁺,Cl^-and SO₄^2-is the highest in the initial stage of eluviation,and then decreased rapidly to zero.(2)Based on the self-made disintegration device,the disintegrating characteristics of loess under different eluviation conditions were studied.It is found that the disintegrating rate is nearly 100%under the influence of water content,salinity and temperature.When the soil water content and salinity are low,the soil disintegration rate under non eluviation condition is higher than that under other eluviation conditions at the same time,and several typical stages of loess disintegration are not significant,while the regularity is opposite to that under the condition of low temperature.When the water content,temperature increase and salinity become saturated,the difference of loess disintegration rate under five eluviation conditions decreases.(3)Based on the statistical results of soil disintegration time and disintegration rate under different eluviation conditions,it is shown that the water content has the greatest influence on the disintegration,and the disintegration completion time and disintegration rate are 67s?201s and 0.71%/s?2.46%/s,respectively water temperature is the second and salinity is the least.The degree of influence of three factors on the disintegration of loess under different eluviation conditions is as follows:water content>water temperature>salinity.(4)Through the indoor collapsibility test,the collapsibility characteristics of loess under different eluviation conditions were studied.It is found that the collapsibility coefficient of loess under different eluviation conditions increased rapidly to the peak value and then began to decrease,and finally became stable with the increasing of pressure.The curve of loess collapsibility coefficient under eluviation condition H=0mm and H=500mm has similar growth range.Taking the pressure corresponding to the collapsibility coefficient equal to 0.015 as the initial collapsibility pressure.It is found that the initial pressure of collapsibility is within the range of 150k Pa?300k Pa when the loess is not eluviated.it is 100?200k Pa and 0?100k Pa When H=500mm?H=1000mm and H=1500mm?H=2000mm.(5)Based on grey correlation analysis,the relationship between loess microstructure parameters and disintegration and collapsibility is obtained under eluviation.It is found that the grain size composition and macropore content have a high correlation with Q₃ undisturbed loess disintegration rate,the grain size composition and pore roundness have the highest correlation with loess collapsibility coefficient.(6)Based on the disintegration test,collapsibility test and scanning electron microscope test of Q₃ undisturbed loess under different eluviation amounts,it is confirmed that the main reasons for the disintegration of the loess are the weakening of the water cementation force and the well-developed pore cracks,while the decrease of the connection strength of the skeleton particles and the increase of the overhanging pores,which lead to the collapsibility of the loess after water immersion and pressure.