基于孔壁形态的锚杆锚固体荷载传递机理及特性分析
Analysis of solid load transfer mechanism and characteristics of anchor based on hole wall shape
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摘要: 在进行锚杆(索)拉拔试验时发现一个重要的力学现象,即当拉拔力加到一定数值,锚杆(索)体未从孔内拔出,岩体试件却伴随巨响或震动,瞬间沿孔壁径向发生整体开裂,由于这种径向压力足以引起整个岩石试件迅速开裂,可见其对锚杆承载力的影响是不可忽视的。针对该现象,通过深入研究岩-岩结构面剪切特性和扩孔理论研究成果中结构面受力剪切过程中必然产生的剪胀效应,分析认为钻孔孔壁形态是产生该径向应力的最主要因素。在适当的假设条件和考虑锚杆钻孔孔壁粗糙形态的前提下,基于非线性Mohr-Coulomb强度准则,结合荷载传递函数法和锚固体-围岩结构面剪胀效应及破坏机理,建立了适应于圆形巷道锚杆锚固体应力传递模型,分别求得破坏和弹性条件下锚固体轴力及剪应力解析式。基于所获得的解析式,深入探讨了锚固体轴力随剪胀角即钻孔孔壁粗糙度变化的分布规律和随圆形巷道应力场切向应力变化的分布规律。同等条件下,剪胀角越大即钻孔孔壁粗糙度越大,锚杆的抗拉拔性能越好,极限抗拉拔力越大;并且注浆锚杆的灌浆压力对锚杆的抗拉拔力有着重要的制约作用,建议在实际锚固工程设计和施工中适当增加钻孔孔壁的粗糙度以提高锚固效果和适当增加灌浆压力来改善锚杆的承载性能。Abstract: In found in testing the anchor rod(rope) drawing is an important phenomenon of mechanics,namely when the drawing force to a certain value,the anchor rod(rope) body did not pull out from the hole,rock specimen with noise or vibration,instantly overall cracking along the radial of hole wall,due to the radial pressure is sufficient to cause the whole rock specimen cracking quickly,it cannot ignore the influence of the bearing capacity of anchor bolt is visible. In view of this phenomenon,through the in-depth study of the shear characteristics of rock-rock structural plane and the dilatancy effect that inevitably occurs in the process of structural plane stress shear in the theoretical research results of reaming,it is concluded that the shape of borehole wall is the most important factor to produce this radial stress. Therefore,based on the proper assumptions and consider the bolt hole under the premise of the rough shape of hole wall,based on the nonlinear Mohr - Coulomb strength criterion,combined with load transfer function method and the anchor solid - structural plane dilatancy effect and failure mechanism of surrounding rock,established the stress transfer model adapted to the circular roadway anchor rod anchor solid,were obtained under the condition of damage and the elastic anchor solid axial force and shear stress. Based on the analytical equation obtained,the distribution law of the axial force of the anchor with the dilation Angle,that is,the roughness of the borehole wall,and the distribution law of the tangential stress with the stress field of the circular roadway are discussed. Under the same conditions,the larger the dilatation Angle is,the greater the roughness of the hole wall is,the better the tensile performance of the bolt is,and the greater the ultimate tensile force is. Moreover,the grouting pressure of the grouting bolt has an important restricting effect on the tensile force of the bolt,so it is suggested to increase the roughness of the borehole wall properly in the actual design and construction of the anchorage engineering to improve the anchorage effect and increase the grouting pressure appropriately to improve the bearing capacity of the bolt.