Experimental Study On The Deformation Of Dynamic Shear Of Unsaturated Loess

Loess, as a typical Quaternary loose sediment, has obvious seismic vulnerability. A great deal of earthquake damage shows that the loess under earthquake is prone to result earthquake subsidence, landslide and liquefaction.In order to simulate the additional stress condition of horizontal soil element during vertical propagation of seismic shear wave, the Xi'an University of Technology developed dynamic simple shear apparatus to carry out dynamic tests of undisturbed loess with different water content. The conclusions are as follows:(1) Under the same conditions of dynamic load, the dynamic shear stress and strain curve of loess decreases with the increase of water content. The vertical compressive stress get greater,the hardening curve of the dynamic shear stress and strain is more exposed. The dynamic shear modulus of loess decreases with the increase of dynamic shear strain. The loess dynamic shear modulus increases when the moisture content gets lower or the compressive stress gets higher.The test points of relationship curve between dynamic shear modulus ratio and shear strain are distributed in a narrow band under different moisture content and compression stress conditions.(2) The damping ratio of undisturbed loess increases with the increase of dynamic shear strain at different humidity conditions. When the dynamic shear strain increases, the damping ratio increases obviously. And when the dynamic shear strain becomes large, it tends to be stable gradually. The greater the moisture content is, the greater the damping ratio is. The influence of the loess damping ratio with the change of dynamic shear strain under different initial compressive stress is not obvious.(3) With the increase of water content, the dynamic strength of loess decreases obviously.Under the same moisture content, the dynamic strength of loess increases with the increase of compressive stress.(4) Under the same dynamic shear stress condition on the seismic subsidence curve of unsaturated loess, the higher the water content is, the greater the coefficient of seismic subsidence is. And the smaller the compressive stress is, the greater the coefficient of seismic subsidence is. Due to the complex structural characteristics of the original soils and the primary pore structure distribution, pore structure is susceptible to suddenly destroy under load, leading to the deformation of the soil.(5) The relation between seismic subsidence coefficient and earthquake time shows that the seismic subsidence coefficient increases with the earthquake time, water content,compressive stress and shear strain. When the earthquake time is less than 30 times, the coefficient of seismic subsidence increases rapidly. And when the earthquake time is greater than 30 times, the coefficient of seismic subsidence increases slowly. With the increase of earthquake time, the greater the water content is, the faster the coefficient of seismic subsidence increases. And the larger the amplitude of dynamic shear strain is, the faster the seismic subsidence coefficient increases.(6) The seismic subsidence coefficient increases with compression stress, shear strain amplitude, water content and earthquake time. The relationship between seismic subsidence coefficient and earthquake time can be fitted by logarithmic function under different experimental conditions. The calculated values of empirical formula are verified. It is more reasonable to calculate the seismic subsidence deformation of test soil samples under certain shear strain, compression stress, earthquake time and water content.