Study On The Strength And Microscopic Characteristics Of Intact Loess Of Gully Land Consolidation Under Eluviation In Yan’an Area

Because of the poor geological conditions in the Loess Plateau,the strong wind erosion and water erosion make its ecological environment vulnerable and soil erosion serious.Yan’an City is a holy place of revolution,and its special narrow geographical conditions restrict the rapid development of the city and social economy.In order to change the situation of limited urban space in Yan’an,large-scale mountain excavation and city construction and gully land consolidation projects,such as the construction of Yan’an new district,have brought new opportunities to the development of Yan’an city.However,a large number of exposed loess slopes have been formed by large-scale mountain excavation and city construction and gully land consolidation projects.In addition,due to the concentrated rainfall in Yan’an area,the stability and disease of the excavated and filled loess slopes have become increasingly prominent.The impact of the changes of physical and mechanical properties and microstructure characteristics of loess under the rainfall leaching on the loess slopes is an important scientific problem to be solved.Therefore,it is of great practical significance and practical value to study the strength and microstructure of loess under leaching.In this paper,under the research background of Nangou gully land consolidation projects in Yan’an,based on the field investigation and the original soil samples obtained,taking the indoor test as the main research method,the original loess is leached first,and then the influence of leach on the Loess characteristics is studied through the conventional triaxial test,lateral compression test and mercury injection test.Through leaching under different conditions,the influence of leaching water on the stress-strain characteristics and shear strength parameters of Q₃ and Q₂ undisturbed loess is discussed,and the influence of leaching water and water content on the compression characteristics and compression indexes of Q₃ and Q₂ undisturbed loess is revealed,as well as the micro pore characteristics of loess under leaching.The research results have a deeper understanding of the change of strength and microstructure of northern shaanxi loess under the action of rainfall,irrigation and other water,and provide a scientific basis for the prevention and control of geological disasters such as loess collapse,slope erosion and landslide.The main conclusions are as follows:（1）Based on the triaxial shear test,the shear strength of Q₃ and Q₂ intact loess under the action of leaching is linearly and positively correlated with the increase of confining pressure,and the function relationship between them is fitted.The shear strength parameters are obtained by fitting method and drawing method,and the difference between them is small,indicating the feasibility of obtaining the shear strength parameters by the fitting method.The cohesion of Q₃ intact loess decreases with the increase of leaching water,while that of Q₂intact loess increases first and then decreases with the increase of leaching water,and leaching has little effect on the internal friction angle of the two（2）Through the confined compression test,the compression characteristics of the loess after leaching at different water content were analyzed,and it was found that the pore ratio of the intact Q₃ and Q₂ loess with different water content decreased rapidly with pressure and then gradually changed,When the water content is low,leaching can increase the intact Q₂loess’s degree of looseness;under the same water content,the intact Q₃ loess in each leaching condition is more loose than the intact Q₂ loess,and the overall compressibility of the intact Q₃ loess is higher;The compression coefficient of intact Q₃ loess decreases first and then increases as the amount of leaching water increases,but the change in compression modulus is the opposite.For the intact Q₂ loess,leaching only has a certain effect on the compression modulus when the water content is low;leaching has a significant effect on compression index of intact Q₂ loess,but the influence on the intact Q₃ loess is not obvious;overall,as the amount of leaching water increases,the influence of water content on each compressiblity index gradually decreases.（3）Based on the particle size test and mercury intrusion test,the effect of leaching on the microscopic particles and pore characteristics of the intaact Q₃ and Q₂ loess was analyzed:the leaching had little effect on the grading characteristics of loess particles with a particle size below 1 mm.After leaching under different working conditions,they are all well-graded soil;leaching has little effect on the pore size and distribution ratio of intact Q₃ loess,but it has a significant effect on the pore diameter and distribution ratio of intact Q₂ loess.