Study Of Creep Mechanics Of Q₂ Loess Under Acidic Environment

Acidic water bodies generated by nature and human engineering activities can significantly affect the physical and mechanical properties of geotechnical bodies.When loess slopes,foundations,and caverns are subjected to acid erosion,their stability will be weakened by the coupled acid-water-physicochemical effects.The creep characteristics and microscopic parameters of acid-etched loess were investigated from macro and microscopic perspectives,and then the creep characteristics and creep models of acid-etched Q₂ loess were investigated by combining rheological model theory and damage mechanics theory.The main findings of the study are as follows.（1）The influence of acid concentration and stress variation on the creep properties of loess was revealed.The tests show that,when the shear stress is certain,with the increase of acid concentration from 0 to 3 mol/L,the long-term shear modulus G_∞of loess gradually decreases,the long-term strengthτ_∞gradually decreases,the instantaneous strain and the creep of stable section increase with the increase of acid concentration;when the acid concentration is certain,with the increase of shear stress 15 kPa step by step,the G_∞value of acid-etched loess first increases and then decreases,and the peak value appears near the shear stress 30 kPa and 45kPa.The peak value of G_∞decreases with the increase of acid concentration,the relative stiffness at the peak is the largest,the strongest resistance to deformation,the creep of loess increases after the peak,the instantaneous strain of acid-etch loess,the creep of the stable section also increases continuously;acid-etching can reduce the stiffness of loess,the creep of loess increases under the coupling effect of acid concentration-shear stress,and the enhancement effect on remolded loess is greater than that of in-situ loess.（2）The improved Nishihara model based on EPS elements can well describe the transient deformation,decay creep,isokinetic creep,and accelerated creep stages of acid-etching loess,and the R² of model fit is 0.920-0.988;the parameters of the EPS five-element creep,model of acid-etching loess show,exponential function y=Ae（-Bx）decay with increasing acid concentration;the acid-etching damage of the creep parameters of acid-etching loess The amount of acid-etching damage to the creep parameters of acid-etch loess increases with increasing acid concentration,and most of the creep parameter damage tends to 1 when the acid concentration increases to 8.0 mol/L.The EPS five-element creep model for acid-etch loess,which is based on the EPS five-element creep model and combined with the acid-etching damage evolution equation,can better describe the characteristics of the whole creep process of acid-etch loess.（3）The acid solution has an obvious influence on the particle size composition and mineral composition of the loess,and the microscopic characteristics of the loess change significantly before and after acid etching.The acid concentration increased from 0 to 3 mol/L,and the content of clay particles in the as-built and remolded loess decreased continuously(the content of powder particles increased relatively,and the content of acid-etched loess was ranked as follows:powder particles>clay particles>fine sand;the average content of quartz in acid-etched remolded loess was 3.35%more than that in acid-etched as-built loess;the content of calcite in the as-built loess decreased from 15.2%to 7.5%,and the content of calcite in remolded loess decreased from 10.8%The contact mode of mineral particles changed from"edge-edge"and"edge-face"to"edge-edge"and"edge-face"contact.The number of pores in the acid-etched primary loess is greater than that in the acid-etched remodeled loess.The number of pores is larger than that of acid-etching remodeled loess;the pore types of acid-etching loess are mainly small pores（radius 1-4μm）and micro-pores（radius<1μm）;the surface porosity of acid-etching loess gradually increases;the increased creep of acid-etching loess is the result of the combined effect of calcite mineral dissolution,change in particle contact mode and increasing pore size.