(1. Institute of Geomechanics，Chinese Academy of Geological Sciences，Beijing 100081，China；
2. Faculty of Engineering，China University of Geosciences，Wuhan，Hubei 430074，China)
Abstract：The cyclic loading test，repeated shear test and scanning electron microscope(SEM) technology were used to study the dynamic characteristics and microcosmic damage mechanism of loess and mudstone in Tianshui area. The dynamic elasticity moduli of loess and mudstone increase nonlinearly with the increasing of confining pressure and are inversely proportional to the damping ratio. When the dynamic shear stress ratio is larger than a certain value，the soil sample fails after the loading cycles reaching a certain number. With the increasing of shearing cycles，the shear strength decreases and finally achieves the residual strength. But with the increasing of confining pressure，the soil occlusion and shear strength increase. The static shear which makes the particles finer belongs to the particle shear trituration mode. The soil particles arranges more smoothly with regular orientation and the inter-particle pores become tight. Under the cyclic dynamic loading，the particles experience the shearing-grinding with the increasing of shear amplitude. The soil particles arranged more smoothly，and the inter-particle pores decreased obviously. The shear plane is shown to be hardened and impervious.
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2017, Vol. 36 
