基于颗粒离散元软件 PFC(particle flow code)和有限差分软件 FLAC(fast Lagrangian analysis of continuum)的离散-连续耦合模型,从细观角度研究了隧洞开挖边界围岩维持自平衡的压力环机制、锚杆支护围岩中性点特征和围岩-锚杆联合承载细观作用机理.结果表明:锚杆支护使开挖边界围岩压力环厚度降低,单根压接触力链量值升高并交织在锚杆周围,锚杆颗粒间平行粘结力远大于围岩颗粒平行粘结力,从细观角度良好地呈现了锚杆-围岩联合承载机制,并说明锚杆支护是保持洞室开挖面稳定的主要承载结构;围岩与锚杆颗粒变形不一致性直观体现了锚杆在隧洞围岩支护过程中的中性点特征;开挖前后临空面附近围岩的颗粒孔隙率下降百分比较无锚杆支护工况显著降低,体现了锚杆为改善开挖引起的围岩松动效应所发挥的重要作用.
Study on particle discrete element simulation and mesoscopic action mechanism of tunnel surrounding rock supported by fully grouted bonded bolt
Using discrete-continuous coupling model based on particle discrete element software PFC(particle flow code)and finite difference software FLAC(fast Lagrangian analysis of continuum),this paper studies the self-balancing pressure ring mechanism of surrounding rock at tunnel excavation boundary,the characteristics of neutral point of surrounding rock supported by anchor rod,and the mesoscopic mechanism of joint load-bearing between surrounding rock and anchor rod from the microscopic perspective.The results show that the rock bolt support reduces the thickness of pressure ring of the surrounding rock at the excavation boundary,but the single compressive contact force chain increases and weaves around the bolt rod.The parallel cohesive force between the rock bolt particles are much greater than that of the surrounding rock mass particles,which presents the joint load-bearing mechanism of rock bolt and surrounding rock mass from the microscopic perspective,and indicates that bolt support is the main bearing structure to keep excavation surface stable.The dis-consistency of particle deformation between surrounding rock and bolt directly reflects the neutral point characteristic of bolt in the process of surrounding rock support of tunnel.The percentage reduction of surrounding rock particle porosity before and after excavation is significantly lower than that without rock bolt supporting,which reflects the important role that bolt plays in improving the loosening effect of surrounding rock caused by excavation.