Experimental Study On Strength Characteristics Of Salt-Bearing Structural Loess

The mechanical properties of loess are closely related to its internal pore development and cementation structure.The loess has high strength during drying and has good engineering properties.This is due to the large pore-skeleton form formed by the loess during the deposition process,which has a certain structural strength.Under the external conditions,the structure of the loess may be disturbed or even destroyed.For example,it is infiltrated by industrial wastewater and urban sewage,and it has physical and chemical interaction with oxides and inorganic salts inside the loess,thus affecting its mesostructure and macroscopic mechanical properties.In this paper,the Q2 undisturbed loess in the loess area of Xi’an is taken as the research object.The representative inorganic salt solution(NaCl,CaSO4,CaCO3)is selected to saturate the undisturbed soil and undergo triaxial compression test.The purpose is to explore the salt migration and change.The effect of salt structural loess strength characteristics;combined with scanning electron microscopy and XDR semi-quantitative analysis,the effects of different types of salt on the structural properties of loess were studied from the perspective of meso-damage;based on the binary medium model of rock and soil,Establish and validate the strength criteria for salty structural loess in the loess area of Xi’an.The main results of the study are as follows:(1)When the loess sample is saturated with a certain concentration of salt solution,the salty pore water in the soil sample will cause different degrees of disturbance to the cementation structure of the soil.The stress-strain curve of the loess sample was analyzed.The deviatoric stress of the undisturbed loess after saturation with the salt solution was higher than that of-the pure water-saturated control sample.However,under the condition of medium-high confining pressure(400kPa),the salt The deviatoric stress of the solution saturated soil was not significantly changed with respect to the control group.(2)Using the insoluble CaCO3 colloid to saturate the undisturbed loess,the peak value of the deviatoric stress under low confining pressure in the triaxial test is close to that of the pure water saturated sample,but the decreasing slope of the softening stage is slower than that of the pure water control group.Because the original loess is destroyed after the structure,the ultra-fine calcium carbonate particles increase the internal friction between the soil particles and improve the shear strength of the soil.(3)SEM and XRD were used to assist in the analysis of the damage of fine structure and salt content in loess samples.The skeleton structure of soil has some damage during saturation,and the contact overlap between particles is less,more The cemented joints were retained,confirming the effect of salt solution saturation on the structural properties of the loess in the triaxial test.(4)Based on the theory of binary medium model,the meso-damage mechanism and macro-mechanical characteristics of salty structural loess are analyzed.The damage variable Rx based on strength condition is determined and the shear contribution rate ξv is determined.The correction and establishment of a suitable application for Xi’an area The shear strength criteria for salty structural loess and verify the applicability of the guideline.