Influence Of Moisture Content And Salt Content On Mechanical Properties Of Undisturbed Loess

A typical undisturbed loess possesses large pores,vertical joints,collapsibility when wetted,unobvious sedimentary bedding.These unique physical and mechanical properties lead to frequent geological hazards in loess area.According to statistical data,about 1/3 landslides in China occur in the loess area.With the continuous agricultural irrigation in the Loess Plateau area,such as Jingyang in Shaanxi,Heifangtai in Gansu,a series of geological hazards,in particular,landslides,have been caused in loess area,resulting in serious unfavorable effects on people's daily life,economic development,and agricultural production,Loess landsliding has become an important factor restricting local economic development,analysis of factors inducing loess landslides and influencing the mechanical properties of loess is important.In this thesis,Heifangtai in Gansu was chosen as the study site,and undisturbed loess samples were taken and laboratory ring shear tests were carried out to investigate the influence of water content and salt content on mechanical properties of loess.The main contents are as follows:(1)Ring shear tests have been performed samples with different water content to study the effect of water content on the shear stress-strain characteristics and strength.It is found that loess with low moisture content showed strain softening behavior,however,with the increase in water content,the corresponding strain softening gradually weakened and changed into strain hardening gradually;under the same normal stress conditions,the peak shear stress increased with the decrease in soil moisture content;The shear strength increases with the water content of loess,softening effect of water on loess is more obvious at low moisture content;with the increase of water content,both cohesion and frictional angle decreased gradually,with significant effect on cohesion compared with friction angle,indicating that the cohesion seems more sensitive to water content.(2)Ring shear tests have been carried out on samples with different salt content to study the effect of salt content on the shear stress-strain characteristics and strength.It was found that under the same normal stress,the salt content is higher,the higher the peak shear stress;when the peak value of the shear stress increases,the shear stress increases faster;the shear strength decreases continuously with the decrease in salt content,the weakening of shear strength is more obvious at high salt content than that at low salt content;with the decrease in salt content,both cohesion and friction angle decreased gradually,however,the decrease in friction angle is less apparent compared with at in cohesion,indicating that the effect of the salt content on cohesion is more significant.