Shear Strength Variation Of Sliding Zone To Resurgent Landslide Under The Conditions Of Water Storage In Three Gorges Reservoir Area

Lots of old landslides have been observed in the Three Gorges Reservoir area.After the water level was raised,many of them might have their slip surfaces’ shear strength decreased and then reactivate.This paper experimentally analyzes the variation of slip soils’ shear strength with reservoir water immersion,taking slip soils from Xietan landslide,Tangping landslide,Qianjiangping landslide,Lianhuatuo landslide and the I#landslide mass near the Changjing river of Huangtupo landslide as an example.The sliding zones of these landslides were all developed in the Jurassic and Triassic strata,which were also confirmed typical facility-sliding strata in the Three Gorges Reservoir area.Therefore,research on the variation of the slip soils’ shear strength is of essential significance in this area.All types of slip soils in this area are gravel-containing clay,containing as high as over 35%of gravel.Since each landslide has different gravel,sand and fine fraction,this paper examined variation of shear strength with different grain compositon.The water level was initially 70m and 145-175m after water storage.Then many old landslides would be immersed.With long time of immersion,the slip soils would be softened and disintegrated and grain composition will change consequently.In addition,long time of saturation could also result in hydrolysis of minerals,and might affect the soils’ shear behavior.Therefore,studying the variation of slip soils’ shear strength with longer saturation time is also of great practical significance.Test results showed that the grain composition greatly impact the soils,residual shear strength and its parameters,of which the gravel fraction and the clay content has the most effect.With gravel content decreased from 35%to 0%and clay fraction increased from 15%to 45%,the tested samples had their residual internal friction angle decreased by 3-5°and residual cohesion declined by 20kPa-60kPa.Moreover,the residual internal friction angle and cohesion had a positive correlation with gravel content and a negative one with clay fraction.Tests results also showed that the longer the saturation time,the more softened all the slip soils were getting at,with a weakening shear strength.And with even longer time of immersion,the strength of the samples was decreased at a slower rate.As different specimens have various mineral composition and microstructure,the time with which the samples lowered their strength most is of great discrepancy.What’s more,the extent at which the specimens lowered their strength varied with grain composition.Coarse grained soils lose the shear strength as the coarse fraction disintegrated producing higher fine fraction.And fine grained groups had their grain composition changed little,and lose their strength mainly because hydrolysis of their minerals.