DETERIORATION LAW AND MICROSCOPIC MECHANISM OF HYDRAULIC CHARACTERISTICS OF UNDISTURBED LOESS IN ILI UNDER FREEZE-THAW ACTION

The freezing damage in Ili area of Xinjiang is serious,especially the landslide disaster is the most significant,which is mainly reflected in the deterioration of hydraulic characteristics of undisturbed loess under freeze-thaw action. However,the deterioration law and microscopic mechanism of hydraulic characteristics are not clear at present. Therefore,this paper carries out the hydraulic test and microscopic test of undisturbed loess in Ili before and after freeze-thaw. The results show that the cementation and structural integrity of loess are destroyed by freeze-thaw action. The effective stress in situ is applied to the undisturbed loess after freeze-thaw,and the loess would produce greater deformation after subsequent water immersion. Therefore,the self-weight collapsibility coefficient of undisturbed loess increases and the void ratio decreases after freeze-thaw. Freeze-thaw action would cause large cracks and large pore size inside the undisturbed loess,and water would be lost from large cracks and large pores during seepage,so the permeability coefficient of undisturbed loess would increase after freeze-thaw. The frost heaving effect in the freeze-thaw cycle makes the free water inside the undisturbed loess become ice,resulting in expansion,which would destroy the cementation and structural integrity of the undisturbed loess,and produce large cracks and large apertures,resulting in the shear strength and cohesion of the undisturbed loess. Repeated freeze-thaw makes soil particles damage,displacement,forming a more complex form of contact,so that the internal friction angle is not significantly reduced.