Under-Compacted Loess Under Hydraulic Interaction Study On Strength Evolution Characteristics

Undercompacted loess is a natural Q3 loess with strong water sensitivity in a loose state.Its physical and mechanical properties are greatly affected by changes in water content.When undercompacted loess is saturated with water,it can form saturated soft loess,which is prone to engineering disasters.At present,there is a lot of research on the changes in soil properties and engineering problems of under compacted loess after water loss.However,the strength evolution characteristics of the soil during the recovery stage of groundwater level and the gradual increase of soil moisture content under overlying loads still need to be further studied.This article is based on the GDS triaxial testing system,and takes under compacted loess with a large pore ratio as the research object.The stress-strain evolution relationship and strength characteristics of under compacted loess during the continuous wetting process under water force interaction are experimentally studied.Combined with SEM experiments,the structural evolution characteristics of under compacted loess under water force interaction are revealed.The research results can deepen the understanding of the strength characteristics of under compacted loess,Provide theoretical and experimental support for engineering practice.The main research results of the paper include:(1)The initial overlying stress,moisture content,and consolidation confining pressure will all have an impact on the stress-strain relationship of undercompacted loess.With the decrease of water content and the increase of consolidation confining pressure,the stress-strain curve of undercompacted loess gradually increases,developing from a strain weak hardening type to a strain strong hardening type.The increase in moisture content also weakens the influence of initial overlying stress on the stress-strain relationship of soil.When the initial overlying stress is 100 k Pa,the height of the stress-strain curve is the lowest,and the shear stress that undercompacted loess can resist under the same degree of deformation is the smallest.Moreover,under this stress condition,the influence of moisture content on the stress-strain relationship of soil is the smallest;(2)The failure shear stress will linearly increase with the increase of consolidation confining pressure and average normal stress.The moisture content and initial overlying stress can not only affect the failure stress conditions of the soil alone,but also interact with each other.The higher the moisture content,the lower the level of strength failure line,and the smaller the influence of initial overlying stress on the strength failure line.When the initial overlying stress is 100 k Pa,the strength failure line is the lowest,and the influence of moisture content on the strength failure line is also the smallest;(3)The cohesion changes significantly with hydraulic conditions,while the internal friction angle changes less.The higher the moisture content,the smaller the cohesion and internal friction angle of the soil,and the smaller the influence of initial overlying stress on the strength parameters of the soil.When the initial overlying stress is 100 k Pa,the strength parameters of the soil are at the lowest level,and at this time,the difference in strength parameters of the soil under various water content conditions is the smallest;(4)Undercompacted loess in its natural state has a certain initial structure,but its structure is unstable and rapidly decays with the development of shear deformation.When the strain exceeds 2%,the structure basically disappears.The larger the consolidation confining pressure,the lower the water content,and the stronger the soil’s structure.When the initial overlying stress is 200 k Pa,the structural characteristics of the soil basically disappear;(5)The evolution of macroscopic strength is actually an external manifestation of changes in soil microstructure.The higher the water content,the simpler the soil particle morphology,and the larger the pore surface area.When the overlying stress condition is 100 k Pa,the soil particles show a state of damage and splitting.When the overlying stress conditions are 200 k Pa and 300 k Pa,the soil structure changes from a primary large pore structure to a layered and dense secondary structure;(6)100k Pa is the critical stress of under compacted loess.Under critical stress conditions,the strength performance of under compacted loess is the worst,and its water sensitivity is the weakest.When the overlying stress condition is less than the critical stress,the mechanical strength of under compacted loess shows a decreasing trend with the increase of overlying stress,and vice versa.