Experimental Study On Dynamic Characteristics Of Heifangtai Remolded Loess Under The Action Of Water Salt(Sulfate)

Loess is widely distributed in China,and its unique porous and weak cementation microstructure makes it exhibit high seismic vulnerability under dynamic action.In the loess region of central and western China,multiple earthquakes have caused serious seismic landsl ide,seismic subsidence and liquefaction of loess.In this study,the remolded loess in Heifangtai area of Yongjing County,Gansu Province was taken as the research object.Through field investigation and sampling analysis,the distribution of water and soil salinity in the area was understood,and the salt swelling test of loess under different soluble salt content was carried out in the laboratory to obtain the salt that caused the most serious damage to the loess.On this basis,a series of dynamic triaxial tests were carried out to study the variation of dynamic strength,dynamic stress-strain curve,dynamic elastic modulus and damping ratio of remolded loess under different confining pressures,water contents and Na2SO4 increments.The main research results are as follows:（1）Through the salt expansion test,it is found that Na₂SO₄ has the strongest salt expansion damage effect on the remolded loess of Heifangtai.Under the same Na2SO4 content,the greater the moisture content is,the more serious the damage of loess is when salt expansion occurs.（2）The dynamic strength of Heifangtai remolded loess decreases with the increase of water content,and increases with the increase of confining pressure.When the water content is 7%and 16%,the dynamic strength increases first and then decreases with the increase of Na2SO4 increment.When the moisture content was 25%and saturated,the dynamic strength decreased first and then increased with the increase of Na2SO4 increment.The changes of dynamic cohesion cd and dynamic internal friction angle φd are similar to dynamic strength.（3）The dynamic stress-strain curve of Heifangtai remolded loess will produce cumulative strain at the early stage of deformation under high confining pressure.With the increase of water content,the dynamic stress-strain curve and dynamic elastic modulus curve will decrease.The greater the confining pressure,the higher the dynamic stress-strain curve and dynamic elastic modulus curve.Under different water content,the dynamic stress-strain curve and dynamic elastic modulus curve of loess vary with the increment of sodium sulfate.The damping ratio increases first and then decreases with the increase of vibration frequency.Confining pressure,water content and Na2SO4 increment will affect damping ratio.（4）Under different loading modes,the pore pressure growth laws of saturated loess remolded by black square platform are different.Under single-stage loading,the pore pressure growth model of saturated loess sample can be expressed by polynomial.Under multi-stage loading,the pore pressure growth model can be expressed by power function.The confining pressure and Na2SO4 increment will affect the pore pressure growth of saturated loess.Under the two modes,the greater the confining pressure is,the slower the pore pressure increases.0.7%sodium sulfate content can promote pore pressure growth,1.4%increment slightly different.