全长锚固锚杆支护软岩巷道围岩承载结构力学响应解析

Mechanical response analysis of surrounding rock bearing structure of soft rock roadway based on full-length anchorage

为研究高应力软岩巷道围岩在全长锚杆锚固后围岩力学承载结构的稳定性,考虑软岩峰后强度软化时的扩容特性和全长锚固锚杆受力边界条件,建立了全长锚固锚杆力学模型,推导得到锚杆受力解析式。并通过将锚固力等效为体积力的形式建立了全长锚固围岩力学模型,将其由浅及深依次划分为锚固残余区、锚固塑性软化区、非锚固塑性软化区及弹性区,推导了各分区的应力表达式。结合工程算例分析了空间效应、扩容系数、锚杆长度和托盘反力等因素对围岩应力和锚杆受力的影响规律。结果表明:受空间效应影响,巷道变形破坏呈现渐进式发育,借此提出了“锚固调控区”的概念,即在全长锚固锚杆支护过程中,围岩的虚拟支护力和锚固力处于此消彼长的状态,从而抑制围岩应力向深部转移,有效减小了塑性区范围。锚杆安装时机越早,作用于杆体的围岩变形越大,且与围岩之间更易形成共同承载体;锚杆轴力与扩容系数呈正比关系,随着扩容系数增大,锚固力增长速率显著加快,保证了锚杆对围岩径向应力的恢复作用;锚杆长度越大,围岩/锚固剂界面粘结范围越广,使得沿杆体的轴力分布及其峰值明显增大,进而使围岩切向应力峰值区向洞壁方向偏移;全长锚固锚杆托盘反力对残余区和塑性区边界的影响较小,其作用主要体现在改善锚杆受力情况,充分发挥锚杆锚固作用及护表能力。

A mechanical model of full-length anchoring bolt is established to study the stability of mechanical bearing structure of surrounding rock in high stress soft rock roadway after full-length anchoring bolt.The model considers the dilatancy characteristics of soft rock post-peak strength softening and the stress boundary conditions of full-length bolt,and the analytical formula of bolt stress is derived.Furthermore,the mechanical model of full-length anchored surrounding rock is established by equivalent the anchoring force to the form of volume force.From shallow to deep,it is divided into anchorage residual zone,anchorage plastic softening zone,non-anchorage plastic softening zone and elastic zone,and the stress expression of each zone is deduced.Combined with engineering examples,the influence of space effect,expansion coefficient,bolt length and tray reaction force on surrounding rock stress and bolt stress is analyzed.The results show that under the influence of spatial effect,the deformation and failure of roadway presents progressive development.The concept of anchorage control zone'is proposed,that is,in the process of full-length bolt support,the virtual support force and anchoring force of surrounding rock are in a state of reciprocal growth and decline,thus inhibiting the transfer of surrounding rock stress to the deep and effectively reducing the plastic zone.The earlier the anchor bolt is installed,the greater the deformation of the surrounding rock acting on the rod body,and the easier it is to form a common bearing body with the surrounding rock.The axial force of the anchor bolt is proportional to the expansion coefficient.With the increase of the expansion coefficient,the growth rate of the anchoring force is significantly accelerated,which ensures the recovery effect of the anchor bolt on the radial stress of the surrounding rock.The axial force distribution and peak value of the rod body will increase with the increase of the length of the bolt and the bonding range of the surrounding rock/anchoring agent interface,and then the peak area of the tangential stress of the surrounding rock will shift to the direction of the tunnel wall.The effect of the reaction force of the full-length bolt tray is mainly reflected in improving the stress of the bolt,giving full play to the anchoring effect of the bolt and the ability to protect the surface,and having little effect on the boundary of the residual zone and the plastic zone.