The Experimental Study On Deformation Characteristics And Microscopic Mechanism Of Malan Loess Collapsibility

Loess is widely distributed in China.The natural structure of loess has high structural strength and is difficult to be compressed.However,after immersion in water,the strength of the soil suddenly decreases and the structure is destroyed,resulting in sudden settlement,which severely restricts the development of various projects in the loess area.Therefore,in order to solve various geological disasters caused by collapsible loess deformation,the first task is to ascertain the characteristics of loess collapsible deformation,and the loess area engineering construction provides a theoretical basis to better complete China's"Belt and Road"development strategy.This article relies on the National Natural Science Foundation project,taking the late Pleistocene(Q₃)loess in Yan'an New District as an example,combined with a large number of indoor collapsible tests,to reshape the undisturbed loess and different dry density,different water content and different pressures A comprehensive study of the collapsible deformation characteristics of loess,and with the help of scanning electron microscope and image processing software,explored its microscopic mechanism in depth,and analyzed the mechanism of collapsible dynamics to provide a theoretical basis for the evaluation of collapsibility of loess in the future.The main research results achieved in this paper include:(1)The original Malan loess is more compressible than the remolded Malan loess,but the former has a greater amount of collapsible deformation after immersion in water and pressure.Microscopic studies have shown that there are more aggregates and large pores formed by the cementation of the original Malan loess particles before collapsing,and the pore distribution of the remolded Malan loess is more uniform than that after the collapsing.Trend of irregular and irregular patterns(2)Changes in initial dry density and water content will not affect the shape of the Malan loess collapsible curve,but the manifestation will change accordingly.The collapsibility of Malan loess becomes weaker with the increase of initial dry density.With the increase of pressure,the loess increases first and then decreases,and the number of small micropores increases.Due to the loose initial structure,the movable range of the particles is larger and the structural deformation is stronger.(3)The collapsibility of the Malan loess becomes weaker as the initial water content increases,and the sensitivity to water also becomes weaker.The study found that the Malan loess with a small initial water content has less pores and more dispersed cement after collapsing,but regardless of the dry density and water content,the number of small pores and micro pores has always been large because of the collapse Although some of the pores are compacted,some of the closed small micropores are retained due to the inaccessibility of water.In addition,some large and medium pores become smaller in the later period,so their number is relatively stable.(4)The properties of the basic functional units of the soil particles and aggregates before the compression deformation of the loess have been determined,and the basic functions of the particles and aggregates during the immersion period of the collapsing process are synchronously transformed and adjusted as the amount of water increases The collapsing process is actually a special compression process that reflects the dynamic effect of the humidification rate under special humidification conditions.