Research On Key Hazard Factors Of Deep Toppling Deformation And Disaster Pattern Of Anti-dip Layered-rock Slope

Under the action of gravity,in the anti-dip layered slope formed by low-strength and single-layer rock mass,the rock mass will be bent and deformed in the direction of the free surface,forming deep toppling deformation,that is,deep toppling deformation.This type of deformation takes a long time to develop and the rock mass is dumped to a large depth,which will eventually form a large-scale geological disaster.Carrying out research on the evolution of deep toppling deformation,analyzing the key hazard factors and disaster pattern of deep toppling deformation,has a guiding significance for a comprehensive understanding of the mechanism and evolution of deep toppling deformation.Therefore,this paper collects the relevant data of typical deep toppling deformation slopes and analyzes the factors affecting the deep toppling deformation.Based on the field investigation and data collection,the toppling deformation body in front of the dam of the Lancang River Gushui Hydropower Station was taken as the research object.Through the centrifuge model test and discrete element numerical simulation software,the evolution process of anti-dip slope under the natural conditions was simulated under the valley trenching,the key hazard factors and disaster pattern of deep toppling deformation were studied.The research results obtained are as follows:(1)The engineering geological model of deep toppling deformation is described.For deep toppling deformation bodies,according to relevant indicators(slope angle of rock slab,maximum tension in the layer,unit tension in the layer,unloading deformation of the rock body,weathering degree of the rock body,longitudinal wave velocity,rock deformation characteristics),the deep toppling deformation body is divided into four areas: extremely strong toppling deformation area A,strong toppling deformation area B(strong toppling deformation upper section B1,strong toppling deformation lower section B2),weak toppling deformation area C,and original rock area D.(2)Combined with the relevant data of typical deep toppling deformation slopes,the influencing factors of deep toppling deformation are summarized into two categories: background factors for deformation appears and hazard factors for disaster occurrs.Background factors for deformation appears include geological environment,stratigraphic lithology,slope foot,and rock formation dip angle.Hazard factors for disaster occurrs include free-surface conditions,earthquake,water storage,rainfall,and artificial disturbance.Using discrete element numerical analysis,it is obtained that the free-surface condition is the key hazard factor for deep toppling deformation.(3)Taking the toppling deformation body in front of the dam of the Lancang River Gushui Hydropower Station as the research object,the prior produced block modules and the excavation step by step were used to simulate the valley trenching under natural conditions.Through the five-stage centrifuge model test of the slope,The disaster process of deep toppling deformation is studied,the results show that:(1)The generation and development of deep toppling deformation of anti-dip layered rock slope can be divided into linear deformation stage,accelerated deformation stage and stable deformation stage;(2)During process of the development of deep toppling deformation,multi-level bending zones can be formed inside the slope,and the development and penetration of the bending zone will affect the final evolution of the slope;(3)The freesurface condition is key hazard factor for deep toppling deformation,which affects the deformation mode,deformation range,and rock deformation characteristics of anti-dip slope;(4)The disaster process of the deep toppling deformation can be generalized as: A rock formation topples;multilevel bending zones form;shear damage occurs throughout a certain bending zone.(4)Taking the same geological profile as the centrifuge test,and using discrete element software,the evolution process of the toppling deformation body in front of the dam of the Lancang River Gushui Hydropower Station was simulated,and the relationship between free-surface angle and the degree of rock topples and deformation failure mode is studied.Selecting quantitative indicators(deformation behavior of slope,structural characteristics of the rock,and macroscopic-damage signs)and qualitative indicators(toppling angle of rock formations,length of tensile crack at back edge,and tensile length in rock formation)to analyse numerical calculation results,the relationships between the degree of rock topples,the depth of rock topples and the excavation angle are obtained.Through quantitative index statistics,the regression relationship between the maximum toppling angle of rock formations,length of tensile crack at back edge,and maximum tensile length in rock formation,the maximum depth of rock topples are obtained.Selecting the maximum toppling angle of rock formations,length of tensile crack at back edge,and maximum tensile length in rock formation and the angle of excavation,the table of the disaster pattern of the deep toppling of the slope are established.