Experimental Study On Structural Characteristics And Deterioration Mechanism Of Malan Loess

In this paper,the Xi'an Malan loess is taken as the explore object,and the structural variation of soil under different water content is studied by the confinement compression test.The micro-area imaging methods such as scanning electron microscopy(SEM)and intelligent 3D digital microscope are used to treat the soil particles.The type of connection and the bonding method are the entry points,and the mechanism of deterioration of the soil structure due to the disturbance action and weak acid dissolution is explored.Firstly,the remodeling times were taken as variables,and the structural differences between the undisturbed and remolded loess samples were compared and analyzed.The results show that the compressive yield stress decreases with the increase of the number of remodelings,which is mainly attributed to the remodeling process.The joints with different degrees of damage,that is,the chemical adhesion damage,cause the effective cementation of the undisturbed loess to be weakened during the remodeling process.In addition,although the degree of remodeling has a one-way superposition increase in the destruction of cementation,the degree of damage of the first remodeling is the most prominent in terms of the single remodeling disturbance effect,and as the number of remodeling increases,The remodeling disturbance has a declining tendency to damage the cement.Secondly,in view of the increasing pollution of acid rain and industrial acid on the Loess Plateau,the structural characteristics of carbonate-rich loess will inevitably change after exposure to acidic environments such as acid rain and industrial acid leakage.In order to reveal the evolution of carbonate structure in the loess caused by acid dissolution,the loess was soaked in 0.2mol·L-1 acetic acid solution,and the microstructural differences between undisturbed,remolded and weakly acid treated loess were compared and analyzed.The results show that the dissolution of carbonate is very important for the structural characteristics of loess.After the carbonate is dissolved,the joint effect between the agglomerates(particles)is seriously degraded,the "wrapped" cementation form is severely damaged,the water stability is significantly deteriorated,and the compressive yield stress is further reduced.Finally,using SEM/EDX Mapping scanning imaging technology combined with thin-film technology,the micro-area of the loess section was imaged and analyzed.A more intuitive particle contact relationship was proposed based on the identification phase.A Mapping image of the mineral elements distribution such as calcite,dolomite,calcium silicate and layered silicate were reflected.Thereby preliminarily identifying the occurrence of carbonate in the loess.The results show that secondary calcium carbonate in loess carbonate is the main material that plays a role in cementation which showing super strong and irreversible cementation.The secondary calcium carbonate aggregates loess mineral particles in the form of “bridge” and “coating”,which helps to reduce the wettability and plasticity of loess.Which also stabilizes the soil structure so that the particles are agglomerated in water without dispersion and improves the mechanical strength of the soil under wet hydration.There is chemical adhesion in loess,and its strong cementation and irreversibility characteristics may be the main reason for the special structural characteristics of loess.This paper will contribute to elucidating the formation and destruction of loess.