Study On The First Fracturelength Of Bedding Slope

The failure of bedding slope is an engineering problem often encountered in railway,highway,mining and water conservancy construction,which is often sudden and destructive.In recent years,scholars have found that the instability of bedding rock slope with weak interlayer is a gradual failure process,and the strain softening of weak interlayer is one of the main factors causing this progressive failure.In this paper,the theoretical calculation formula and finite element calculation method of the first fracture length are obtained by means of theoretical analysis,numerical calculation and engineering example verification.The sensitivity of rock and soil mechanical parameters and slope geometric parameters in the first fracture length is analyzed and verified in practical engineering.The main work and conclusions are as follows:(1)theoretical calculation: a generalized one-dimensional slope model is established,and the excavation unloading stress of elastic slope is obtained by referring to the wedge calculation theory.Based on the force of micro-element of slope body,the force balance condition of slope body under the action of strain softening of weak interlayer is analyzed.The effects of critical shear displacement of slip zone,length of rigid-plastic section,excavation unloading stress,thickness of cut layer,elastic modulus of slide body,peak shear strength of slide zone and residual shear strength of slide zone on slope force are considered.According to the stress equilibrium condition,the formula of the first fracture length of bedding slope with weak interlayer strain softening is derived.(2)finite element calculation: a total of 135 working conditions are calculated through the theoretical calculation formula and finite element method of the first fracture length of bedding slope.the influence of strain softening of weak interlayer on the displacement,stress and plastic zone of slip zone and slope is discussed.after the comparative analysis of the calculation results,it is determined that the plastic zone length of slip zone is used as the calculation method of the first fracture length in finite element calculation.(3)based on the influencing factors such as rock and soil mechanical parameters and slope geometric parameters,the sensitivity analysis of influencing factors is carried out in theoretical calculation and finite element calculation,respectively.the results of sensitivity analysis show that the rock dip angle of bedding slope and the strain softening of shear strength parameters of sliding zone soil are the main factors affecting the length of the first fracture.(4)the results of theoretical study and finite element calculation show that the calculation of the first fracture length of bedding slope is suitable for the compound failure mode of sliding zone shear yield and trailing edge tension crack、 the dip angle of rock layer is small、and the weak interlayer is obvious.(5)the comprehensive analysis of three practical projects,namely,the Pingle interchange landslide of Renmuxin Expressway,the bedding slope of Bawan Expressway and the landslide of Chengdu Tianfu International Airport Expressway,is carried out to verify the formula for calculating the first rupture length of the bedding slope proposed in this paper.The results show that the theoretical formula established in this paper is reasonable and reliable and can be used in the design and calculation of practical bedding slope engineering.