隧道围岩-衬砌接触面剪切特性模拟研究

Simulation Study on Shear Characteristics of Tunnel Surrounding Rock-Lining Contact Surface

探究隧道围岩-衬砌接触面在不同法向应力及不同粗糙度条件下的剪切特性规律,对进一步研究隧道围岩与衬砌间的相互作用及岩体稳定性具有重要的理论和工程意义。为考虑粗糙度条件,利用分形理论,通过改变分形公式中的分形维数D及分形粗糙度G生成5种不同接触面,基于二维颗粒流程序(PFC^(2D)),建立接触面数值剪切模型,尺寸为150 mm×150 mm。开展同一接触面在不同法向应力下,数值模拟剪切试验及不同接触面在同一法向应力下的数值模拟试验;将数值剪切试验与室内剪切试验获得的剪切应力-剪切位移曲线进行对比,验证数值剪切模拟的可靠性。研究结果表明:(1)数值模型剪切破坏产生的裂隙主要集中于中间接触面处,破坏后的应力主要集中于接触面粗糙度最大处,破坏裂纹可分为剪切裂纹和张拉裂纹,其中张拉裂纹占主要优势;(2)剪切应力-剪切位移过程曲线存在爬坡、啃断、滑移三大阶段,具有明显的峰值强度和残余强度,法向位移随着剪切位移的增加而增大,产生剪胀效应;(3)随着法向应力增加,剪切和张拉裂纹数量增加,破坏现象越明显,峰值强度和残余强度增大,剪胀效应减小;(4)随着粗糙起伏度增大,即分形维数D的增大或者分形粗糙度G的减小,破坏裂纹数量增加,其中张拉裂纹增加较明显,峰值强度和残余强度增大,剪胀效应增大。

Investigating the shear characteristics of the contact surface between tunnel surrounding rock and lining under different normal stresses and roughness conditions has significant theoretical and engineering importance for further research on the interaction between tunnel surrounding rock and lining,as well as the stability of rock mass.To consider roughness conditions,fractal theory was adopted to generate five different contact surfaces by changing the fractal dimension D and fractal roughness G in the fractal formula.Based on the two-dimensional particle flow code(PFC^(2D)),a numerical shear model of the contact surface with dimensions of 150 mm×150 mm was established.Numerical shear tests were carried out for the same contact surface under different normal stresses and for different contact surfaces under the same normal stress.In order to verify the reliability of the numerical simulation,shear stress-shear displacement curves obtained from a typical numerical shear test were compared with those obtained from the laboratory shear test.The research results showed that:(1)The cracks generated by shear failure in the numerical model were mainly concentrated at the middle contact surface,with stress after failure mainly concentrated at points with the greatest contact surface roughness.The failure cracks could be divided into shear cracks and tensile cracks,with tensile cracks being predominant.(2)Shear stress-shear displacement curves exhibited three stages:climbing,cutting and sliding,with obvious peak strength and residual strength.Normal displacement increased with increasing shear displacement,resulting in dilatancy effect.(3)With the increase of normal stress,the number of shear and tensile cracks increased,failure phenomena became more pronounced.Peak strength and residual strength increased,and the dilatancy effect decreased.(4)With increasing roughness undulation,i.e.,an increase in fractal dimension D or a decrease in fractal roughness G,the number of failure cracks increased,especially tensile cracks,as well as peak strength and residual strength.The dilatancy effect also intensified.