节理岩体锚杆的综合变形分析

Synthetical deformation analysis of anchor bolt in jointed rock mass

在总结国内外对节理岩体中锚杆加固机制的试验研究和理论探讨基础上,综合考虑锚杆的切向和轴向变形能力,建立节理锚固锚杆在剪切荷载作用下的变形模型,将节理锚固锚杆的变形区划分为弹性变形段和挤压破坏段,引入表征挤压破坏段长度的变量,对锚杆与岩体的相互作用机制进行理论分析,推导了剪切荷载与剪切位移和轴向荷载与轴向位移的关系。通过分析锚杆的屈服破坏形式,得到了确定挤压破坏段长度的方法。最后,通过算例分析了挤压破坏段长度与锚杆直径、岩体强度、锚固角度等参数的关系,得到了以下结论:(1)节理锚固锚杆抗剪作用的实质是锚杆调动岩体的抗压强度抵抗节理切向荷载。在抗压强度较高的硬岩中,挤压破坏段局限于节理面附近,锚杆影响范围小;而在抗压强度较低的软岩中,挤压破坏段较大,而且会产生较大的剪切变形,锚杆影响范围较大。(2)锚杆屈服破坏形式与岩质和锚杆直径有关。硬质岩体发生剪切屈服,而较软岩体中容易发生弯曲屈服;小直径锚杆一般直接剪切屈服,而大直径锚杆可能发生弯曲屈服。锚杆屈服破坏后出现塑性铰,挤压破坏段范围在节理一侧约为直径的1～2倍,继续增加剪切荷载,挤压破坏段长度不再增大。(3)随岩质的不同,锚杆锚固节理的最优锚固角变化较大。岩质较硬时,最优锚固角度较小,反之则较大。

Based on the former experimental and theoretical researches on the reinforcement mechanisms of anchor bolt in jointed rock mass at home and abroad, and comprehensive considering of the tangential and axial deformability of anchor bolt, a deformation model of joint bolts under shear load is proposed. The deformation of joint bolts is divided into two parts： elastic deformation zone and crushing failure zone. A variable is introduced to express the length of crushing failure zone. Mechanism of interaction between bolts and rock mass is analyzed. Relationships between tangential load and tangential displacement, and axial load and axial displacement are deduced respectively. Through the analysis of yield failure model of bolt, a method to calculate the length of the crushing failure zone is proposed. Finally, a calculation example is presented to study the relationship between the length of crushing failure zone and the parameters, such as the bolt diameter, the rock mass strength, anchorage angle and so on. It is concluded that： （1） The shear resisting function of joint bolts is actually that the bolts arouse the compressive strength of rock mass to resist the shear load of the joint plane. In the hard rock with higher compressive strength, the crushing failure zone is limited near the joint plane and the influence area of bolt is small; while in soft rock with lower compressive strength, the length of crushing failure zone and shear deformation and the influence area of bolt is larger. （2） The yield failure mode of anchor bolt is related to rock properties and diameter of the bolt. Shear yield occurs in hard rock and bending yield occurs in soft rock. Bolt with little diameter usually go through shear yield and bolt with large diameter may go through bending yield. After yield failure, the plastic hinge appears. The length of the crushing failure zone on one side of the joint is 1-2 times of the bolt diameter, however, it no longer increases with the increasing of shear load. （3） The optimal anchor supporting angle of joint anchor bolt varies with rock properties. Hard rock has a smaller anchor supporting angle and the soft rock has a larger one.