Research On The Influence Of Excavation Conditions And The Law Of Excavation Deformation Response For Anti-dip Slope

The annular area around Qinghai-Tibet Plateau,where mountains are mostly with steep slope and gorges are dense,which mainly hydroelectric energy projects of China situate in.Due to the frequent fluvial erosion,high geo-stress field,and intense tectonic activity,the zone arises many slope geological hazard,threatening the projects and neighbouring inhabitants.Anti-dip slope is one special kind of slope hazard.Naturally anti-dip slope arises toppling that is a long geological evolution process.However,human usually make it short by various excavation activities,giving rise to that the slope may fail even though it is stable before excavation.At present,few study that involve in anti-dip slope and excavation was conducted.It is obvious that influence of excavation activity on anti-dip slope differ from dip slope and oblique slope,hence the conclusion obtained might be circumscribed.Aim at excavation problem of anti-dip slope,this article,having collected many toppling slope cases being in connection with excavation,adopting statistical analysis approach,summarized the toppling development laws of anti-dip slope,as well as typical toppling development conditions and features are raise.On the basis of the statistical result,this thesis explored influence of different excavation conditions via adopting numerical experiments,and the sensibility of excavation factors were analyzed in grey correlation method.Finally,a typical excavation slope case was studied to verify the conclusions having acquired previous.In this paper,several kinds of analysis approach are employed,and the research details are stated about as follows:(1)By collecting 40 domestic typical excavation anti-dip slope cases,the characteristics of regional distribution and the slope geological characteristics were analyszed,and put forward the following toppling conditions for anti-dip slope:(1)slope direction and stratum dip direction tend to be opposite,and the included angle of them is no less than 120°;(2)slope angle(β)is no less than 30°,while strata dip angle(α)is more than 40°;(3)85°≤α+β≤130°;(4)lithology:soft-hard interbeddings,upper-hard lower-soft ground,weak rockmass or jointed hard rockmass;(5)slope is horizontally uncontinuous and there are incise or free face in lateral.(2)By conducting two sets of numerical experiments,one of which has a middle strata dip angle while another is steep.Under natural conditions,the deformation of the former is unapparent and the latter topple prominently,which displacement reach6.32m.Based on the numerical experiments,the influence on anti-dip slope of excavation factors were analyzed,including excavation location-ΔH,excavation height-h,excavation gradient-ωand excavation rate-v.Adoptting grey correlation method(one analysis approach)excavation factors are ranked as follows according to influence:(1)middle dip slope,h>ω>ΔH>v;(2)steep dip slope,h>ΔH>ω>v.(3)Summarizing two sets of excavation numerical experiments,following conclusions could be achieved.(1)deformation region of stratum all locate above the normal plane(is known as Aydan plane);(2)slope is easier to topple when it has a steeper strata dip angle,and the former is much easilier fail than the latter when toppling appears;(3)The depth of toppling deformation is shallower in middle dip slope than the steep,and which fail more abruptly.(4)Through a field investigation deformation and fracture characteristics,deformation monitoring data after phaseⅠandⅠof a typical excavation anti-dip slope in a hydropower station,the slope deformation mainly develop above step3240m,and the deformation upstream side is larger than downstream side.By analyze the deformation process and feature of the slope,slope failure mechanism(top unloading rip--middle part topple—bottom collapse)can be concluded,and the the amount of failure mass is about 300000-350000m~3.(5)Based on the excavation slope model of a hydropower station,the slope deformation response under different excavation conditions were analyzed,and the slope is destroyed under the first excavation condition.Under the second excavation condition the slope deformation is not significant.Under the premise of guaranteeing the stability,The excavation volume of recommended condition is lower than the second excavation condition.