Research On Instability Mechanism Of Beveled Slope With Variable Inclination Angle In Red Bed Area

The variable-inclination bedding slope is a common type of slope in the red bed,especially in the barrier fold structure area in eastern Sichuan.Controlled by the conditions of“upward steepness and slow down”variable dip angle structure,special lithology combination and other conditions,the instability mechanism of red layer variable dip angle bedding slope is complicated.The deformation failure mechanism and evolution process of this kind of slope are studied.The prediction and evaluation of landslides and the prevention and mitigation of landslides in layers have certain theoretical significance.The Xinglangpo slope in Xuanhan County,Sichuan Province is a variable-inclination bedding slope composed of interbedded layers of sand and mudstone with different thicknesses.With the evolution of the valley landform,the slope has undergone multiple deformation and failures.Recently,under continuous heavy rainfall,a slip-bending deformation failure occurred on the slope on September5,2004,which provided a typical example for studying the deformation mechanism of the bedding slope with varying dip angles.This article takes this landslide as the research object,based on the systematic investigation of the geological environment conditions of the landslide area,the basic characteristics of the landslide,especially the deformation and fracture characteristics of the landslide,using geological analysis,mechanical analysis and numerical simulation methods to comprehensively study the Xinglangpo landslide many times Deformation and failure mechanism and its evolution process.The following main research results have been achieved.?1?Under the control of the barrier folds in the east of Sichuan,the Xinglangpo slope is a"upward steep and gentle"type variable-inclined bedding slope,and the inclination of the rock layer gradually slows down from 32°at the top of the slope of510m to the front 14°at 270m elevation.The slope is composed of sandstone and mudstone of different thickness in the middle Jurassic Shaximiao Formation?J₂s?,with a single layer thickness ranging from 0.15m to 1.5m.At present,the thickness of the single layer of the shallow layer of the slope?sliding and bending deformation zone?is mostly 0.15m-0.3m,and the thickness of a few layers is 0.5m-0.7m.?2?The Xinglangpo slope has been deformed and destroyed many times in the geological history.The old landslide accumulations are mainly distributed in the elevation of 270m-385m below the slope.The scale of I#old landslide accumulation is about 63×10⁴m³;the size of II#old landslide accumulation is about 262.8×10⁴m³.According to the analysis of the slope structure and the structure characteristics of the old landslide accumulation body,the formation of the old landslide is a variable-inclined bedding slope.Under the erosion condition of the rivervalley,the weak interlayer in the slope body is exposed at the foot of the slope,and under heavy rainfall conditions,the slope Along with the weak muddy interlayer,the bedding slip failure occurred,and its deformation failure mode was slip-pull type.3DEC numerical simulation software was used to reproduce this deformation failure process of the old landslide.?3?"9.5 landslide"occurs at the trailing edge of the old landslide accumulation area at the upper part of the slope,with an elevation of about 360m-510m,a thickness of about 8m,an area of about 26.23×10⁴m²,and a volume of about 2.0984million m³.Its occurrence was affected by heavy rain for a hundred years from September 3 to 5,2004,and its deformation failure mode was slip-bend.The deformation of the landslide generally shows that the sliding body at the top of the slope slides along the weak interlayer,and the lower part bends and bulges at an elevation of 360m-430m,and even breaks out.According to the different sliding distances,the deformation of the slope can be divided into left and right areas.In the left area,the slip distance is 45m.There are two uplift and lower bend zones in the lower part of the sliding body.The upper bend uplift zone is located at an elevation of410m to 420m.It is characterized by rock layer slip-bend-break shear failure,forming steep ridge landforms;The belt is located at an elevation of 360m to 380m,which is characterized by a curved uplift of the rock layer with an uplift height of 10 m-15m,without breaking and breaking.The sliding distance in the right area is 30m,and the rock sliding-bending deformation occurs in the area of 420m-430m elevation in the middle of the landslide area,and the rock layer bends and breaks.?4?According to the slope structure and deformation and failure characteristics,a geological-mechanical analysis was made on the formation mechanism of"9.5landslide"."9.5 landslide"is under the condition of rainfall,under the influence of the old landslide accumulation foot of the front edge,the rock layer on the trailing edge of the Xinglangpo slope is under the combined action of its own weight and the groundwater buoyancy force.Using the mechanical calculation formulas of Sun Guangzhong and Li Shusen,the effects of rock layer dip angle,single layer thickness and rock physical and mechanical parameters on the critical slope length of Xinglangpo 9.5 landslide collapse failure were analyzed.The greater the dip angle of the stratum,the smaller the critical slope length of the stratum buckling;the greater the thickness of the single layer of the stratum,the greater the critical slope length of the stratum buckling;the greater the elastic modulus of the rock mass and the Poisson ratio,the critical slope of the stratum buckling The greater the length;the greater the weight of the rock,the smaller the critical slope length of the rock collapse.?5?The 3DEC software was used to simulate and analyze the instability mechanism of the"9.5 landslide"and its slip-bending deformation process,and the rock slope dip angle and single layer thickness on the sliding deformation of the"9.5landslide"rock layer on the Xinglangpo slope Impact.The effect of rock layer dip angle on the deformation slope of the landslide is analyzed by establishing two different sliding surface forms?straight sliding surface and variable dip angle sliding surface?.The straight sliding surface slope only undergoes one slip bending deformation and variable dip angle sliding The surface undergoes two sliding and bending deformations.The greater the single layer thickness h of the rock layer,the larger the critical slope length Lcr of slip bending deformation,that is,the higher the critical slope height for maintaining the stability of the slope.?6?The deformation and failure mode of the bedding slope with variable dip angle in Xinglangpo changed from the early bedding slip-cracking type to the later slip-bending type.The transformation of slope deformation and failure mode is mainly affected by topography and landform factors?slope type,slope,slope height and free surface development of Xinglangpo slope?,structural factors of slope body?variable dip angle rock layer occurrence,sand and mudstone unequal thickness interlayer Lithology combination and rock layer thickness,etc.?and the control of rainfall factors.