Methods For Seismic Stability Of Consequent Bedding Rock Slope And DDA Simulation Of Landslide Process

With the implementation and advancement of western development strategy and One Belt One Road initiative,all kinds of large infrastructures in southwestern China and along the Silk Road economic belt are under construction or have been built(e.g.the western route project of the South-to-North water transfers,the West-to-East gas pipeline project,the West-to-East electricity transmission project,the high dam projects in the source region of three rivers,the Sichuan-Tibet railway project).And these projects are threatened by serious earthquake-induced geological disasters,especially the failure of consequent bedding rock slopes triggered by earthquakes.However,the dynamic failure mechanism and the evolution process of earthquake-induced bedding-plane landslides are complicated and not very clear until now.Thus,the analyses of the seismic stability and the evolution process after failure are of great scientific significance and practical value,because they are vital to revealing the dynamic catastrophic mechanism,and further providing scientific evidences for the designs of slope stabilization and disaster mitigation measures.Considering the different failure mechanisms of consequent bedding rock slopes under earthquakes,this thesis aimed at proposing the corresponding methods for seismic stability evaluation and runout analysis after landslide initiation.The main research work can be classified into the following several parts.(1)By incorporating the Vector Sum Method(VSM)in the Discontinuous Deformation Analysis(DDA),the vector sums of resistant forces and sliding forces along the potential failure surface were determined based on the actual stress state of seismic rock slopes.Then the time history of safety factor and the permanent displacement obtained simultaneously by DDA-VSM could be used to evaluate the seismic stability of consequent bedding rock slopes against sliding comprehensively.(2)Assuming that the slope instability(or landslide initiation)was accompanied by the instantaneous shear strength degradation of discontinuities,a relationship between the transient stability of the slope and the shear strength parameters of discontinuities was established.And a state-dependent shear strength degradation model was presented based on the relationship.Comparing to the existing kinematics-dependent shear strength degradation models,the proposed state-dependent model is easier to establish and implement due to the simpler relationship with less parameters to be determined and the lower requirement for relevant test techniques of slope-forming materials.(3)By incorporating the proposed state-dependent shear strength degradation model of discontinuities,the DDA method was improved and used to model the Daguangbao landslide triggered by Wenchuan earthquake.The results illustrate that the shear strength degradation of discontinuities affects the evolution process,travel distance,and deposition pattern of seismic landslides significantly.Besides,comparing to the direct impacts of earthquake forces on the landslide process,the impacts of shear strength degradation of discontinuities induced by the earthquake are more significant.(4)The buckling failure of stratified rock slope was considered to be a multilayer beam stability problem,an analytical method based on the energy equilibrium theory was presented for the buckling stability analysis under complex environmental loadings.Comparing to the existing methods,the proposed analytical method could provide a more reasonable result for buckling stability assessment,because it was capable to consider the multilayered distribution characteristics and size effects of stratified rock slopes.Through the sensitive analyses,it can be concluded that the effects of rock strength,rock deformation modulus,Geological Strength Index,layer thickness and disturbance degree of rock mass on the flexural buckling stability were more significant than that of rock material constant and slope angle.(5)From the intrinsic mechanism of buckling deformation and failure of rock layer,the strategy of rigidity reduction was put forward and realized in the DDA method for buckling stability assessment.Based on the simulated transition process of single rock layer from the slipping state to the buckling state,the buckling failure process of the stratified rock slope and its migration and deposition processes after failure are investigated.(6)Aimed at the possible overturning failure of rock slopes under extreme earthquakes,an analytical method relied on moment balance theory was presented to assess the stability of rock slopes against overturning.Through parametric study,the effects of various factors,such as the earthquake,the surcharge,the hydrostatic water pressure,the tension crack depth and so on,were investigated in detail.The results suggest that the hydrostatic water pressure and the earthquake play dominant roles in the overturning failure of rock slopes.To conveniently evaluate the seismic stability against overturning for a rock slope with water-filled tension crack,a series of design charts are provided,in which the combinations of various parameters are of engineering interest.