Experimental Study Of Large Centrifuge Simulation On The Mechanism Of Deformation And Failure Of Red-bed Huashengdi Landslide In Yiliang County Of Yunnan Province

The bedding rocky landslides in the Red-bed zone often obviously featured large scale areas,complex mechanism and serious damage.The Huashengdi landslide in Yiliang County located in the center of new town construction is a typical bedding rocky landslide induced by rain.Once this kind of landslide starts,it will exert a significant influence on the area.The history of the landslide and its mechanism of deformation and failure,therefore,need to be studied further.And the physical experiment with large centrifuge can simulate the whole process of landslide deformation and failure,reproduce the evolutionary process and restore the change of pore water pressure and stress state of slope,thus having incomparable advantages.Taking the Huashengdi landslide as research object,this paper describes the simulated experiment on rainfall by using centrifuge.Through a series of physical simulation experiments with centrifuge,the whole process of the deformation and failure of landslide prototype in peanut field has been reproduced.Moreover,the evolution process of deformation and failure and the characteristics of changes in pore water pressure and earth pressure have been analyzed,thus drawing the seven conclusions as follows.(1)Through the collection of preliminary reconnaissance data and field survey,the geological environment and conditions as well as the characteristics of Huashengdi landslide have been found out.The Huashengdi landslide which is directly caused by rainfall belongs to rainfall-induced landslides and takes the shape of a “round-backed armchair” on the whole.The lithology mainly falls into the sand and mudstone of Suining group of Middle Jurassic(J2sn)and the landslide accumulation horizon of Quaternary system.The slide bed and its right edge possess a characteristic of interbedded sandstone and mudstone and the attitude of rocks is 300°?15°.(2)Based on the data about landslide and field review,the terrain and strata before the Huashengdi landslide slides has been restored,serving as a model for establishing the experimental model of centrifuge before the Huashengdi landslide slides.And the mudstones used in the experiment were taken from the landslide prototype in Huashengdi.(3)Monitoring results of deformation and failure characteristics of the slope during the experiment with centrifuge show that the cracks first appear at the trailing edge of the slope.And as the infiltration of rainfall,the cracks on the trailing edge spread and extend further,and then develop into the main controlling cracks towards the inside of the slope.The leading edge creeps and shoves as well as deforms,thus shear failure occurs at the foot of slope.(4)Monitoring results of earth pressure on the slope indicate that the soil pressure reduces successively from the leading edge and central part of the slope to its trailing edge.The change of earth pressure value is closely related to the deformation of the slope.The infiltration of rainfall leads to an increase in the water content of slope,the weight of rock and soil and the downward force increases accordingly,resulting in the concentration and increase in thrust of leading and central part of the slope,the former part in particular.The deformation first begins to emerge when there are cracks on the trailing edge of the slope,and the leading edge is dominated by extrusion due to the slowness of sliding surface.Besides,the distribution of earth pressure is consistent with the development of deformation.(5)Monitoring results of pore water pressure on the slope suggest that the pore water pressure dissipates quickly under the rainfall conditions and the pore water pressure is smaller than in the natural state when the trailing edge of the slope suffers pull crack and failure.In addition,during the process of rainfall,the groundwater gradually infiltrates into and collects at the leading edge and central part of the landslide,which causes the declining pore water pressure from the leading edge and central part to trailing edge of the slope.(6)According to the analysis of results of centrifuge simulation experiment,it can be seen that the deformation and failure process of the slope can be roughly divided into four stages,namely,the expansion and penetration of pull crack on the trailing edge,the development of secondary cracks in superficial layer of the slope caused by the creep deformation of the slope toe on the leading edge and the intensive development of secondary cracks in superficial layer of the slope as well as the overall instability stimulated by rainfall.(7)Research shows that the deformation and failure mode of Huashengdi landslide is a composite action model that combines the deep pull crack-creeping-shearing-slip type with creeping in superficial layer-pull crack-shearing type,in which the motion mode in deep layer belongs to push type while that of the superficial layer is mainly pull type.As the rock stratum on leading edge become slower,the deformation in deep layer of original slope starts with forming pull cracks on the trailing edge at first and then creeping and shearing along the weak plane towards the leading edge.Meanwhile,the shear stress converges toward the foot of the slope.Finally,a penetrating sliding surface forms which is triggered by rainfall and the slope quickly slips and presents shearing failure.While the deformation in superficial layer begins to emerge with the creep and deformation of the above leading edge and the deformation of the slope toe increases,which in turn lead to or pull cracks on the back of the slope.At that time,a great number of secondary cracks in superficial layer of the slope develop,and the deformation zone gradually penetrates and generates shear failure under the effect of interstitial water pressure caused by the rainfall.