Test Study Of The Structural Characteristics And Strength Characteristics Of The Acidic Environment

Loess is a typical structural soil widely distributed in northwest China.The loess has strong collapsibility and water sensitivity due to its internal structure of large pores and weak cementation,which is the fundamental reason for causing humidification deformation and progressive failure of the project.Under the condition of acidic solution erosion,the difference of loess structural evolution will lead to the difference of strength and deformation characteristics loess.This paper applies the GDS triaxial instrument to perform conventional triaxial consolidation drainage shear tests on loess with different consolidation bearing pressure,solution type,solution concentration and initial structure.Based on the characteristics of the structural parameters of loess after the normalized structure degree,the test defines the evolution law of loess structural damage caused by acid solution erosion,systematically reveals the internal mechanism of structural damage of loess induced by acid solution infiltration,and analyzes the relationship between loess structural damage and shear yield,strength and deformation.The research results provide theoretical basis and experimental support for engineering construction in acidic environment of loess region.The main research achievements of this paper are as follows:（1）Conventional triaxial tests under different consolidation confining pressures,different initial states and different acidic solutions were carried out.The test results show that under low confining pressure,the stress-strain curves of soil eroded by aqueous solution and 1mol/L oxalic acid solution show softening type,while under other conditions,they are hardening type.The stress-strain curves of the loess eroded by acetic acid and nitric acid solution decrease gradually with the increase of solution acidity and concentration.The stress-strain curve of the loess etched by oxalic acid solution increases with the increase of solution concentration.（2）Under the same conditions,the stress-strain curve relationship shows that the original loess is larger than the remolded loess and larger than the saturated loess.The results indicate that both flooding and disturbance damage the primary mechanism of loess,and the shear strength of loess decreases with the gradual weakening of the initial structure.（3）According to the double-line method and Mohr-Coulomb strength criterion,this test measured the structural yield stress and shear strength indexes of loess under different initial states respectively.The yield stress and shear strength of the loess etched by acetic acid and nitric acid solutions increased first and then decreased with the increase of acidity,and the shear strength and yield stress of the loess etched by oxalic acid solution were higher than those of acetic acid and nitric acid solutions.（4）The stress ratio structural parameter m η was selected to describe the structural evolution of loess during shearing.The results show that the mη-εs curve of the loess eroded by acidic solution decreases gradually under different conditions,and the decay rate is gradually gentle with the increase of shear strain.The regularity of structural parameters becomes more obvious after normalized treatment.The test revealed the relationship between texture index muand shear strength index c,φ;and systematically justified the internal mechanism of the difference of loess strength caused by acid solution infiltration.（5）Through the SEM test,the differences in the micro structure of loess in different initial states and under different acidic solution conditions were analyzed,and the intrinsic mechanism of the infiltration of acidic solution on the soil body was clarified.It is also revealed that the essence of some differences in soil macro mechanics and strength characteristics is that acid solution infiltration leads to changes in soil pore size,particle connection form and soil composition.