Study On Dynamic Parameters Of Loess And Its Influencing Factors

The 1920 Haiyuan earthquake induced a large number of landslides,collapse,avalanche lakes and other geological disasters,indicating that seismic damage exist in loess area and its seismic response was very sensitive.The special structure of loess directly affected the static and dynamic characteristics of itself.So researching of dynamic parameters of loess under seismic loading and its relationship with loess'special structure was necessary.This thesis used 1#?Ningxia?,2#?Lanzhou?,3#?Yan'an?as samples.Through a number of tests,the physical properties,grain size,mineral composition,microstructure features,quantitative structural parameters,structural strength,shear strength,dynamic pore water pressure and dynamic parameters of three loess were researched.The relationship between dynamic parameters and structural and influence factor of dynamic strength feature were also analyzed.The results as followed:?1?Different methods of loess saturation had huge influences on its structure.In the process of saturation,CO₂ and high back pressure significantly weaken the loess strength.Back pressure saturation method was used in this thesis,considering samples completely saturated when B value reach 0.8?back pressure?_b=370kPa?.?2?3#sample had the minimum porosity and pores among the three loess,particles steadily connected by inlaying each other.And its structural far bigger than1#and 2#that connected by grain skeleton support.Otherwise,the area where 3#from had larger precipitation compared with other two areas.Undering this conditions for a long period,its particles had stronger adhesion stress and gradually reinforced until forming flocculent structure,which made loess had a better strength to support external force load.The area where 2#from had smaller precipitation,loess particlesing lack of the mixture with the water,this made particles had weak cementation,kept better shape,individual particles remain independent,made loess a unstable condition and smaller structural.1#loess had high void ratio,more mesopore and medium-pore.But the increasing of mineral content in soil native structure reinforced the cementation between particles.1#had a bigger structural than 2#.1#had high clay mineral and soluble salt level,which made loess sensitive to water.With the raising of the water content,dissolving of clay mineral and soluble salt made the strength of 1#decreases fastest.Its structural is smaller than 2#at this time.?3?The special structural of loess leaded to the difference of dynamic parameters.Under same condition,3#had the highest shear strength,structural strength,structural quantitative parameters,dynamic modulus of elasticity and dynamic strength.Under low water content???15%?,1#had higher dynamic parameters than 2#.Under high water content,1#had lower dynamic parameters than 2#.Dynamic parameters of three loess decreased with increasing of water content.?4?Loess initial dynamic elastic modulus?maximum dynamic elastic modulus?had relationship with initial structural parameters.The plasticity index,void ratio,water content represent different loess dynamic modulus and damping ratio was use in establish formula.Loess static strength and dynamic strength had correlation,so we could use static strength to get dynamic strength.Through dynamic and static parameter contrast,shew that loess mechanical parameters greatly attenuated under seismic loading,thus indicating loess with high seismic vulnerability.?5?Under same condition,loess dynamic strength and parameters rised with dry density,consolidation ratio and frequency rising,and with water content rising.The samples under same condition get different dynamic strength when using different standard.The choicing of the standard had huge influence on dynamic strength,so it was important to choose the appropriate standard.