破碎岩石锚固结构承载力学特性模型试验研究

Model test study on bearing mechanical properties of anchored gravels

为揭示破碎岩石锚固结构承载失稳机制,探索支护构件与破碎岩石相互作用下锚固结构内部应力演化规律,通过自主研制的试验系统开展不同预紧力下破碎岩石锚固结构的自稳及再承载模型试验,研究破碎岩石锚固结构承载力学特性与变形破坏特征,分析破碎岩石锚固结构自稳及再承载全过程预紧力对结构内部压力和锚杆锚托力时空响应的影响规律,探讨破碎岩石锚固结构自稳及再承载失稳机制,并从强化破碎岩石锚固结构内部力链网络角度出发,提出以恒高预紧力、强均压护表、高刚度及合理支护密度为核心的巷道冒顶防控理念。结果表明:破碎岩石锚固结构自稳的临界锚杆预紧力约为3 N·m,其自稳过程内部压力在上层中部出现突增,并向四周扩散维持稳定,而在下层中部出现突降,这与结构内部力链网络重分布密切相关。随着锚杆预紧力的增大,锚固结构内部压力突增更显著、锚托力突降数值有所减小,表明高预紧力的破碎岩石锚固结构容易形成强力链网络,低预紧力的破碎岩石锚固结构力链网络较弱且离散显著,难以自稳及承载。破碎岩石锚固结构承载过程中出现频繁的大幅应力跌落,预紧力越大的模型应力跌落数值越大,且最大承载位移往往大于其峰值位移,对应的荷载也低于峰值荷载。破碎岩石锚固结构承载过程中内部压力显现基本与自稳过程一致,并与其变形破坏模式相对应,下层中心位置形成的穹窿顶空腔破坏了力链网络,致使岩块沿模型中心向四周扩散迅速冒落。锚杆锚托力则随着承载变形的增大而持续降低,临近结构中轴线的锚杆锚托力降低数值要远大于远离结构中轴线的锚杆。高锚托力是保证破碎岩石锚固结构力链网络的必要条件,预紧力越高,锚杆锚托力突降数值越大,但在突降后仍能承受较长时间的荷载。

To reveal the instability mechanism of deep anchored broken surrounding rock and to explore the internal stress evolution law of the anchored structure under the interaction of support components and gravels,the selfstabilization and reloading model tests of anchored gravels under different pretightening forces were carried out through a self-developed test system.The bearing mechanical properties and deformation failure characteristics of anchored gravels were studied.The influences of the pretightening force on the spatiotemporal responses of internal pressure and bolt anchoring force within structure during the self-stabilization and reloading processes of anchored gravels were analyzed.The mechanisms of self-stabilization and reloading instability of anchored gravels were explored.Based on strengthening the internal force chain network of anchored gravels,a concept of roadway roof fall control was proposed with constant height preload,strong pressure equalizing support,high stiffness and reasonable support density as the core.The results show that the critical pretightening force for self-stabilization of anchored gravels is about 3 N·m.A sudden increase in internal pressure is occurred in the upper-middle part during self-stabilizing process and it spreads outwards to maintain stability.In the lower-middle part,there is a sudden decrease,which is closely related to the redistribution of internal force chain network within the structure.The higher the pretightening force,the more prominent the sudden increase in internal pressure and the less the decrease of the anchoring force.This indicates that high pretightening force is more likely to form a strong force chain network,while low pretightening force result in weak and scattered force chains to damage self-stabilization and loading.During the loading process of anchored gravels,there are frequent and significant stress drops.The larger the pretightening force,the greater the model stress drop,and the maximum loading displacement is generally greater than its peak displacement,and the corresponding load is also lower than the peak load.During the loading process of anchored gravels,the internal pressure behavior is basically consistent with the self-stabilization process,and corresponds to its deformation and failure mode.The dome cavity formed at the center of the lower layer destroys the force chain network,causing the rock mass to spread and fall rapidly along the center of the model to the surrounding areas.The bolt anchoring force decreases continuously with the increase of the loading deformation,and the value of the anchoring force reduction near the central axis of the structure is much greater than that far away from that.High anchoring force is a necessary condition to ensure the force chain network of anchored gravels.The higher the pretightening force,the greater the sudden drop in anchoring force,but after the sudden drop,the structure can still withstand a long time of load.