复合顶板锚杆受力特征及临界长度研究

Stress characteristics and critical length of bolt in composite roof

为探究锚杆在复合顶板岩层中的受力分布特征,以2种岩层形成的复合顶板为例,考虑复合顶板力学性质和岩层厚度对锚固体受力分布的影响,构建复合顶板锚杆受力分布模型,分析复合顶板锚杆在受拉作用下的剪切位移、轴力和剪应力分布特征,揭示锚固体受力变形特征受岩层力学性质和厚度影响的变化规律。结果显示:锚固体在岩层之间的接触面处存在剪切位移和剪应力的突变,从而造成复合顶板易沿接触面区域产生拉伸破坏;此外,上位岩层与直接顶部岩层之间弹性模量比值越大,锚固体受力变形越集中,且越靠近接触面;直接顶板岩层厚度越大,复合顶板的剪应力和剪切位移最大值越靠近直接顶板岩层。基于复合顶板锚杆的受力分布,定义剪应力残余系数,建立复合顶板锚杆临界锚固长度计算模型。当剪应力残余系数一定时,计算得到的临界锚固长度随顶板厚度增加而增长。最后通过复合岩层锚杆受拉数值模拟对比分析,锚杆的受力变形特征及求取的临界锚固长度与理论计算结果具有一致性,检验了理论计算结果的合理性。

In order to explore the force distribution characteristics of bolt in composite roof strata,with the composite roof formed by two kinds of rock strata as an example,the stress distribution model of the composite roof anchor has been constructed considering the mechanical properties of the composite roof and the influence of the thickness of rock strata on the stress distribution of the anchor.The distribution characteristics of shear displacement,axial force and shear stress of composite roof anchor under tension have been analyzed,and it has been revealed that the deformation characteristics of anchor is affected by mechanical properties and thickness of rock stratum.The results have shown that there is a sudden change of shear displacement and shear stress at the interface between rock layers,which makes the composite roof prone to tensile failure along the interface area.In addition,the greater the ratio of elastic modulus between the upper rock layers and the direct top rock layers,the more concentrated the stress deformation of the anchorage,and the closer it is to the contact surface.The greater the thickness of roof rock, the closer the maximum shear stress and displacement of composite roof are to the direct roof rock. Based on the stress distribution of composite roof anchor, the residual coefficient of shear stress has been defined, and the critical anchorage length calculation model of composite roof anchor has been established. It is found that when the residual coefficient of shear stress was constant, the calculated critical anchorage length increases with roof thickness. Finally, through comparative analysis of numerical simulation of composite rock bolt, the stress and deformation characteristics of the bolt and the calculated critical anchorage boundary length is consistent with the theoretical calculation results,which verified the rationality of the theoretical calculation results.