Analytical Model For Shear Mechanical Of Bolted Rock Joints And Slope Stability Under Water-induced Degradation

Rock bolt has become the mainly structural reinforcement means of high slope and underground cavern of water conservancy and hydropower projects in China.In Southwest China,only one large-scale hydropower project has used millions of bolts,the long-term effective operation of bolt system directly affects the operation safety of power station.The service state of hydropower slope rock mass is controlled by environmental factors,slope rock mass type and structure,mechanical properties of boltage structure and other factors.Under the action of rainfall and reservoir water level fluctuation,the deterioration of mechanical properties caused by rock mass damage and bolt corrosion is inevitable,which is bound to affect the long-term stability of boltage structure on hydropower slope.The boltage design theory of slope has limitations at present,and the deterioration of boltage structure performance is not fully considered.In view of the long service life of large-scale hydropower projects,whether the rock mass boltage structure system of hydropower slope can meet the requirements of long-term service is one of the hot and difficult topics in current research.At present,scholars mainly focus on the axial pull-out performance of grouting bolt,while the research on shear performance of bolt used to reinforce unstable rock mass is not enough,and the research on the deterioration of shear performance of bolt considering water is even less.The establishment of an effective analysis model for the shear mechanical properties of rock mass with bolted rock joints is helpful to analyze the mechanical response of the bolt under shear action.At present,the research on the shear mechanical model of bolted rock joints is in the basic stage,many influencing factors and generalized models are not fully considered,multi-dimensional monitoring data support is not enough,and a unified theoretical system has not yet been established.In the study of slope stability,there is also a lack of consideration on the shear performance of bolt.Field monitoring shows that a large number of bolt bolts in engineering have failed by shearing.Therefore,in the evaluation of slope stability,the lateral shear capacity of bolt bolts can not be ignored.In view of the inadequacy in the study of shear mechanical properties and mechanical model of boltage joints and the stability of boltage slope,the shear mechanical model of boltage joints and the stability analysis of boltage slope under water degradation are taken as the main research line in this paper,and the deterioration mechanism of shear properties of boltage joints under water degradation through the combination of laboratory test and theoretical analysis are systematically studied.The shear mechanical model of bolted rock joints considering the evolution of shear parameters and the shear mechanical model of bolted rock joints considering water-induced deterioration are established;the time-varying stability analysis method of slope considering the shear failure mode of bolt is proposed;finally,the long-term stability of the boltage slope on the left bank of Xiangjiaba is evaluated based on FLAC^3D.The main research results and innovations of this paper are summarized as follows:(1)The degradation law of rock and bolt strength parameters under water induced degradation is studied.The 180 day dry wet cycle and long-term soaking deterioration tests of rock and bolts are carried out.The strength parameters mechanical tests of rock and bolts are carried out every 30 days,and the corrosion amount of bolts are measured.The degradation law of strength parameters of rock and botls are obtained.The main mineral composition of sandstone is analyzed by X-ray diffraction and the microstructure degradation characteristics of sandstone is observed by SEM.Based on the analysis of the microstructure degradation characteristics of sandstone,it is found that the water induced degradation destroy the microstructure of sandstone,which is mainly due to the connection and expansion of the original pores and the newly formed pores with the continuous wetting drying cycle and long-term immersion,which increase the permeability of sandstone,the size and number of pores in the medium.(2)The degradation law of shear properties of bolted rock joints under water induced degradation is studied.Based on 3D laser scanning instrument and 3D engraving instrument,the natural 3D joint surface is reproduced on the original rock,and the manufacturing process of botled rock joint sample is proposed.Based on the experimental study of the influence of anchoring parameters on shear characteristics,the indoor shear tests of anchorage joints after water induced deterioration test are carried out by selecting appropriate anchoring parameters and three-dimensional morphology of joint surface,and the shear strength parameters of bolted rock joints,the evolution process of bolt axial force,the deformation characteristics of bolt and the fracture characteristics of bolt are studied.The experimental results show that the decrease of shear strength is partly due to the decrease of fracture energy and friction coefficient between mineral particles.The small protrusions on the rough surface of joints are easily worn and sheared when they are affected by water.The decrease of rock strength leads to the decrease of deformation energy of constraint bolt,and the corresponding shear displacement increases gradually when the bolt breaks.(3)A shear mechanical model of bolted rock joint considering water induced deterioration is established.Based on Mohr Coulomb criterion,the shear load calculation formula of bolted rock joint is established.Combined with the shear strength parameter evolution equation,the analytical model which can reflect the whole process of shear load of bolted rock joint is established.Then,the strength and direction of shear force parameters and axial force parameters of rock bolt in the analytical model are theoretically deduced.Combined with the damage model of joint shear performance under water-induced degradation and the strength parameter degradation model of rock and bolt,the shear mechanical analysis model of anchor joint considering water induced degradation is established.Finally,the reliability of the model is verified by the shear test of bolted rock joints in Chapter 3.The results show that the model can well predict the shear load shear displacement law of bolted rock joints under water induced deterioration.(4)A time-varying stability analysis method considering shear failure mode of bolt is proposed.Considering the transverse shear action of the bolt,three modes of tensile failure of the free section of the bolt,debonding failure of the grouting body and the bolt in the anchorage section and tensile shear failure of the bolt on the sliding surface are determined,and the calculation formula of the safety factor of the anchored slope is modified.Based on the reliability method,the reliability model of the slope series system is established,and the time-varying model of the mechanical parameters of the slope is analyzed and established.The time-varying failure probability of the anchored slope is calculated by the Monte Carlo stochastic simulation method.Finally,the sensitivity analysis of influencing factors of slope time-varying stability is carried out.(5)The stability analysis of the left bank slope of Xiangjiaba hydropower station is completed.Based on the definition of safety factor adopted in FLAC^3D finite difference analysis software,the long-term stability analysis of the left bank slope of Xiangjiaba hydropower station is carried out,and the variation of safety factor when the slope is running for 40 years is calculated.The long-term stability analysis of Xiangjiaba left bank slope based on reliability method is carried out.Firstly,the general position of the potential sliding surface of the slope is searched by FLAC^3D software,and the position of the sliding surface is determined by combining with the joint occurrence and the position of the weathering zone.Then,the change of the failure probability of the anchored slope is calculated by combining with the time-varying stability analysis method in this paper.Based on the above research results,the main innovation achievements of this paper are summarized as follows:(1)The degradation mechanism of shear properties of bolted rock joints under water-induced degradation is revealed.Through the water-induced deterioration test of rock and bolts degradation effect and mechanism of strength parameters under the action of water-induced deterioration of rock and bolts are studied;through the indoor shear performance degradation test of bolted rock joint,the degradation law of shear performance of bolted rock joints is studied,and the variation characteristics and degradation law of axial force and shear force,interface mechanics and deformation of joint surface in the process of shear deformation of bolt are deeply analyzed The response law and degradation law reveal the degradation mechanism of shear mechanics of bolted rock joint under water induced degradation.(2)The shear mechanical model of bolted rock joint under water-induced deterioration is established.Based on the shear load calculation formula of bolted rock joint with shear strength parameter evolution,the shear force and axial force in the process of bolt shear are deduced,and the shear mechanical model of bolted rock joint is established.Combined with the deterioration model of bolt and rock strength parameters and the shear damage model of joint surface,the shear mechanical analysis model of bolted rock joint considering water-induced deterioration is established.(3)A time-varying stability analysis method considering shear failure mode of bolt is proposed.On the basis of considering the shear failure mode of bolt,three basic failure modes of bolt and the corresponding comprehensive failure mode of anchor slope are determined,the resistance characteristics of each failure mode of bolt are analyzed,and the calculation formula of safety factor of anchor slope is modified;according to the randomness and time-varying characteristics of mechanical parameters of slope,based on the reliability theory,a time-varying stability analysis method considering the shear failure mode of bolt is proposed.