Study Of Applicability Of Strength Parameters Of Sliding Zone Soil Based On Effective Vertical Stress Level

The shear strength parameters of soil in slide zone are indispensable factors for stability evaluation and countermeasure design to landslides. Because it directly affects the reasonable determination about the size of control engineering, the safety character of the project and prevention engineering scheme. At present, it is considered commonly that the average shear strength at the slip surface of the reactivated landslide drops to the residual strength during sliding, but the present research showed that the residual strength could be recovered to some extent during unmoving. When studying stability evaluation or the strength parameters of sliding surface for large-scale landslide, ancient landslide and reactivated landslide, at present it was easy to neglect the stress effect that dead weight of overlying landslide, so based on previous research results and the environment conditions of slip soil, this paper grasped the landslide characteristics of displacement largely and sliding periodically and used ring shear apparatus to do ring shear test, taken from the Xuechengzhen reactivated landslide (the third landslide) located along the Zagunao River, Sichuan Province. After the sliding surface which was residual strength state was consolidated, strength parameters became recovered strength, and to study recovered strength could not detach residual strength. The characteristics of the shear strength at the slip surface in the reactivated landslide ware simulated and clarified, so its experimental design was that the remoulded soil samples were consolidated at30,150,200and300kPa effective normal stress separately, and then made the samples shear displacement largely until shear strength reached the residual strength state, and continuing re-consolidated at the same effective normal stress, and the last re-sheared until the strength parameters became recovered strength. That is to say, it was simulated the stress and practical mobile morphology of reactivated landslide, use the experimental process that consolidation-ring shear testing in the laboratory under the experiment of large displacement shear re-consolidation-re-shear using the moving soil mass. Then taken the soil sample of shear surface after ring shear test and did Size analysis test, Soil Liquid limit and Plastic limit combined determination test in the laboratory, and X-ray diffraction analysis test for the quantitative analysis of mineral content of slip soil.It analyzed characteristics of physical mineralogy and results of shear test about the sample after the test, and obtained that the shear strength of soil in slide zone of Xuechengzhen reactivated landslide with silt and sand showed the differences degree of attenuation and recovery under the different size of effective normal stress. When the lower effective normal stress σn’(?)150kN/m2, the strength attenuation and recovery were all more obvious; but when the higher effective normal stress σn’(?)150kN/m2, the strength attenuation was more obvious, while the strength recovery rate was very low, less than3%, negligible. Considering the influence about sliding surface strength under the effective normal stress, based on the proposed method for determining and selecting the residual strength and recovered strength parameters depending on the magnitude of the effective normal stress, the residual strength parameters and recovered strength parameters were determined according to the magnitude of overburden pressure in the actual landslide, as well as those strength parameters were reasonably chosen and applied to the stability analysis of the Xuechengzhen landslide, achieving reasonable results corresponding to the current situation of landslide stability. The proposed method for determining the residual strength and recovered strength parameters depending on the magnitude of the effective normal stress might be useful and rational for the reactivated landslide. The method may throw some new light on rationally choosing strength parameters of slip zone soil for the reactivated landslide.