Research On Shear Mechanism And Strength Analysis Method Of Rock-concrete Interface

With the policies and strategies of double carbon,strong transportation country and urbanization construction being put forward and implemented,the fields of water conservancy engineering,transportation engineering and high-rise construction in China have been developed rapidly.The stability of concrete dams and rock foundations,the reinforcement capacity of anchor rods and the bearing capacity of rock-socketed piles in these engineering fields are strongly dependent on the shear characteristics of the rock-concrete interface.The establishment of a reasonable roughness quantification model and the clarification of its shear mechanism are the prerequisites for the accurate assessment of the interface shear characteristics.However,there is a lack of quantitative models that can reasonably describe the interface roughness for engineering applications,and the shear model for calculating and analyzing the interface strength still needs further improvement.In view of this,this paper starts from studying the quantitative model of roughness at the rock-concrete interface,combines experimental and theoretical research methods to further investigate the interface shear mechanism,so as to establish an improved shear model and propose the corresponding method to predict and analysis the interface strength.This paper first analyzes the shear characteristics and load transfer mechanism of rock-concrete interface under normal stiffness constraints.To address the problem that the existing regular triangular model fails to reflect the variability and dispersion of asperity dimensions in the analysis of shear characteristics of natural interfaces,two corresponding improved quantization models are established based on the theory of arithmetic progression and normal distribution,respectively.The methods for determination the key parameters in the quantification model are also given.In addition,based on the energy method,the expressions of shear stress under the sliding dilatancy mechanism,the displacement proportionality coefficient and residual friction coefficient under the residual shear mechanism are derived,and the collapse load of the local asperity is solved using the limit analysis theory.Secondly,to further clarify the shear mechanism of rock-concrete interface,a series of shear tests were designed and carried out for different quantization models with regular,isotropic and normal distributions for three different triangular asperity interfaces with the help of constant normal stiffness shear apparatus.The test results show that the regular triangular interface shows synchronous damage,and the shear of the interface can be divided into two shear processes:sliding dilatancy and residual shear,and the shear stress and shear displacement show obvious linear shear characteristics;on the contrary,due to the difference of asperity size,the arithmetic progression and normal distribution interfaces show obvious asynchronous damage,and the shear of the interface can be divided into three processes:sliding dilatancy,progressive damage,and residual shear,and the shear stress and shear displacement show obvious nonlinear shear characteristics.In addition,the shear response of the normally distributed interface is more ductile than that of the regular and arithmetic progression interfaces.Then,the linear shear model R1 is established based on the quantized model of regular triangular asperity,the sliding dilatancy mechanism and residual shear mechanism of horizontal sliding;on this basis,an improved linear shear model R2 is established by further considering the residual shear mechanism of the relative motion between the asperity and the scrap;the upper bound theory is adopted to solve for the critical shear displacement used to distinguish the sliding dilatancy process from the residual shear process in the linear shear model.Then,the flow chart of the solution method for interface strength using the two linear shear models is given.To verify the rationality of the above two linear shear models,the two shear models are compared and validated with the shear test results of the regular triangular interface,and the comparison indicated that the shear model R2 predicted the residual strength with better accuracy than R1.After that,the effects of the initial normal stress,normal stiffness,rock cohesion,internal friction angle,half-chord and inclination of asperity on the τ～s curve,peak strength τu,residual strength τr and critical shear displacement sc are analyzed and summarized in detail.Again,the nonlinear shear model M1 and M2 are established based on the arithmetic progression,normal distribution,theory and irregular rock-concrete interface shear mechanism,respectively.The critical displacement determination conditions for the three shear processes of the two nonlinear shear models are solved using the limit analysis theory,and the evolution equations of the number of asperities under the sliding dilatancy and residual shear mechanism are further derived.On this basis,the methods for solving interface strength using the two nonlinear shear models are proposed respectively.Then,the prediction errors of peak and residual strengths and critical shear displacements for the two nonlinear shear models were obtained by comparing the theoretical predictions and experimental observations.The comparison results show that both types of nonlinear shear models overestimate the residual strength,and the reasons for the overestimation are analyzed in detail.The effect of boundary condition parameters,rock strength parameters and interface roughness parameters on the interface shear characteristics are explored separately using the control variable method.Finally,to address the overestimation of the interface residual strength for the previous nonlinear model,the modified nonlinear shear models are developed by further considering the local lift-off mechanism in the shear process of irregular interface.Based on the residual shear mechanism,the determination criterion of local asperities lift-off and the evolution equations of the number of asperities under the sliding dilatancy,residual shear and lift-off mechanisms are established.On this basis,the methods for solving interface strength considering the local asperities lift-off are given respectively,and the essential reasons of the lift-off mechanisms affecting the interface strength are summarized by analyzing the number of asperities and the stress evolution process.The results of model validation show that the modified nonlinear shear model improves the prediction ability of the interface strength,especially the accuracy in predicting the residual strength.