Study On Deformation And Failure Mode Of Joint Rock Slope With Inclined Weak Interlayers Under Excavation

Joint rock slope with inclined weak interlayers is very vulnerable to instability under external disturbance,which may cause huge economic losses and casualties.Excavation not only directly reduces the supporting force around the excavation face,but also causes the stress redistribution,stress differentiation and stress concentration of the slope,which has become a common factor triggering landslide.Taking Jietai temple II slope as an engineering case,the deformation and failure mode of joint rock slope with inclined weak interlayers under excavation is studied in this paper.Based on the analysis of the existing geological data,the structural characteristics of the slope were identified by combining the high-density resistivity method and the drilling method.Based on Hoek-Brown empirical criterion,the shear strength,elastic modulus and tensile strength of jointed sandstone were determined by field joint information investigation and drilling core analysis.The shear strength of soft carbonaceous mudstone was obtained by large-scale shear test.Finally,the excavation process of slope was simulated by FLAC 3D software.The variation characteristics of deformation,plastic zone,stress and stability coefficient of slope with excavation process were analyzed.The following conclusions are drawn:(1)The deformation and failure modes of slope under excavation are closely related to the slope structure,and the deformation and failure are mainly controlled by faults and carbonaceous mudstone interlayers.The outcrop of carbonaceous mudstone and rebound effect of unloading is the direct cause of landslide.And the excavation of the fifth,seventh and ninth step has great influence on the stability of the slope.(2)Under the excavation,the slope shows a traction failure mode along the multistage carbonaceous mudstone interlayers.Because of the exposure of weak interlayer and the rebound effect of unloading,the front slope slides,and then tracts the back slope sliding.Three tension cracks may be formed after slope excavation.The whole landslide body can be divided into four sliding blocks with three tension cracks as its boundary,and each sliding block has a carbonaceous mudstone interlayer as its main sliding surface.This mode of deformation and failure provides a basis for the design of reinforcement measures.It also can provide reference for similar slope engineering.(3)The proposed reinforcement location and timing optimize the reinforcement design scheme of the slope.The combination reinforcement measures of "pre-stressed anchor cable + anchor cable anti-slide pile" can effectively prevent large-scale deformation and failure of this kind of slope.Faults and carbonaceous mudstone interlayers should be the key control objects.Before slope excavation,it is suggested that a row of anchor cable anti-slide piles should be arranged on the slope surface near F2 fault,the fourth step and the eighth step to provide supporting force to slope.In the course of slope excavation,it is suggested to install pre-stressed anchor cables on the third,fourth,seventh and eighth step for active reinforcement.Prestressed anchor cables and anchor cable anti-slide piles can constitute a joint reinforcement measure to jointly resist the sliding thrust along the carbonaceous mudstone interlayers.