基于实际围岩变形的全长锚固锚杆杆体应力分布特征分析

在全长锚固锚杆支护过程中,锚杆与围岩之间会相互作用,进而引起锚杆应力分布变化。为探究全长锚固锚杆正常支护过程及临界失效时锚杆应力分布规律,以围岩变形为基础,建立了锚杆-围岩相互作用模型,推导出锚杆在正常支护过程中及临界失效时轴力及剪应力沿杆长分布解析表达式,进而获得了轴力及剪应力沿杆长分布曲线。并在考虑锚杆及锚固剂弹性模量、锚杆及锚固剂横截面面积等锚固参数的条件下分别分析了围岩条件、锚杆长度、托锚力对全长锚固锚杆杆体应力分布的影响。结果表明:在全长锚固锚杆正常支护过程中,杆体应力分布符合中性点理论;影响锚杆轴力、剪应力分布的因素有围岩条件、锚固参数、托锚力;在锚杆正常支护过程中,全长锚固锚杆杆体应力分布符合中性点理论,随着围岩变软,锚杆为了限制变形,中性点向孔口方向移动且所受轴力、剪应力增大;托锚力影响杆体应力分布,托锚力越大,轴力分布越不均匀,且孔口到中性点处剪应力越小,中性点到杆端剪应力越大。所以在工程实际中可实时监测锚杆托锚力,依靠本文理论依据可深入揭示锚杆支护过程中受力特征;在锚杆支护临界失效时,围岩越坚硬,剪应力及轴力越大,且分布更加集中;锚杆长度影响全长锚固锚杆的支护性能,但在锚杆长度超过一定范围后再增大锚杆长度并不能显著提升锚杆的锚固效果。

Analysis of stress distribution characteristics of fully anchored bolt based on actual surrounding rock deformation

During the fully anchored bolt support process,the interaction between the anchored bolt and the surrounding rock will cause the stress distribution of the bolt to change.In order to explore the stress distribution of the bolt in the normal support process and critical failed support process,the interaction model of the anchored bolt surrounding rock is established based on the deformation of surrounding rock.The analytical expressions of axial force and shear stress along the length of the bolt during the normal support process and critical failed support process are derived.Furthermore,the distribution curves of axial force and shear stress along the length of the bolt are obtained.Also,the effects of rock condition,anchor length and anchorage force on the stress distribution of fully anchored bolt are analyzed under the condition of anchorage parameters such as anchorage modulus,anchorage and anchorage cross sectional area.The results show that during the normal support of the full length anchor bolt,the stress distribution of the rod conforms to the neutral point theory.The factors affecting the axial force and shear stress distribution of the anchor include surrounding rock conditions,anchoring parameters and anchoring forces.During the normal support process,the stress distribution of the full length anchor bolt body conforms to the neutral point theory.As the surrounding rock becomes soft,the anchor rod moves to the orifice direction and the axial force and shear stress increase.Large anchoring force affects the stress distribution of the rod,the greater the anchoring force,the more uneven the axial force distribution,and the smaller the shear stress from the orifice to the neutral point,the greater the shear stress from the neutral point to the rod end.Therefore,in the actual project,the bolt anchoring force can be monitored in real time.The theoretical basis of this paper can reveal the force characteristics during the bolt support process.In the bolt support critical failure,the harder the surrounding rock,the larger the shear stress and the axial force and the more concentrated the distribution is.The length of the anchor affects the support performance of the full length anchor bolt,but the increase of the bolt length after the bolt length exceeds a certain range doesn’t significantly improve the anchoring effect of the anchor.