Study On The Evolution Law Of Three-Dimensional Microstructure And Catastrophe Mechanism Of Loess Liquefaction

The Loess Plateau has a special geographical location,complex geological structure and has long been in a zone of strong seismic development.The frequent occurrence of loess liquefaction hazards seriously threatens the safety of people’s lives and property,so it is of great significance to investigate this hazard of loess seismic liquefaction for major projects and town construction in the Loess area.In this paper,based on conventional geotechnical tests,dynamic triaxial tests and three-dimensional microstructure tests,the liquefaction characteristics of loess,three-dimensional microstructure features and the evolution of the three-dimensional microstructure of loess at different liquefaction stages are studied to further reveal the disaster mechanism of loess seismic liquefaction,and the following results are achieved:I.Liquefaction characteristics and three-dimensional microstructure features of loess(1)The dynamic pore pressure and dynamic strain of saturated loess are gradually accumulated and developed,and the growth curves of dynamic pore pressure can be divided into parabolic and S-shaped,and there is attenuation of dynamic stress when liquefaction breaks down,and the pore pressure does not reach the effective surrounding pressure.The pore pressure ratio of liquefaction damage increases with the increase of clay content,while the dry density is the opposite;the vibration frequency of liquefaction damage is positively correlated with the clay content,dry density and inhomogeneity coefficient.(2)The three-dimensional microstructure of the loess has a certain geographical pattern,with particle size,pore space and pore throat decreasing from north to south and particle sphericity increasing.The distribution of sub-angular particles in loess is the most,pores are mainly medium pores,large pores are less,pore throats are concentrated in 0-9μm,and the dominant pore throat channel length is 20-25μm.II.Three-dimensional microstructure evolution law of liquefied loessThe three-dimensional microstructure evolution rules of different liquefaction stages are relatively similar.The quantified results show that the diameter and length-to-short axis ratio of the particles decrease during liquefaction,but not obviously,and the sphericity increases,and more particles with large roundness appear.Liquefaction destroys the native pore structure,pores are filled and dismembered,pore throats with large areas and long passages evolve into pore throats with small contacts and short distances,and the content of medium pores and micro pores increases significantly.III.Microscopic disaster mechanism of loess liquefaction(1)Based on the relative entropy theory,the sensitivity of each microstructural parameter to the liquefaction of loess is analysed,and the results show that the response of pores to seismic liquefaction is significantly greater than that of particles.The sensitivity of each microstructural parameter is ranked as follows: pore radius > pore throat channel length > pore throat radius >particle sphericity > particle equivalent diameter.(2)Seismic liquefaction of loess is a process of particle rearrangement and strong pore dismemberment.The large and long pores provide the innate conditions for seismic liquefaction,the particles transition from point contact to surface contact and indirect contact,and the shelf structure is transformed into a mosaic structure.