Analytical model of shear mechanical behaviour of bolted rock joints considering influence of normal stress on bolt guide rail effect

Abstract

Rock bolts have been widely used in slopes as a reinforcement measure. Modelling the shear mechanical behaviours of bolted rock joints is very complicated due to the complex factors that affect the axial force and shear force on the bolts. Rock bolts under shear action exhibit the guide rail effect; that is, the rock mass slides along the rock bolt as if the rock bolt is a rail. The normal stress can inhibit the guide rail effect and reduce the axial force on bolts. However, this factor is not considered by the existing analysis models. Shear tests of bolted joints under different normal stresses were carried out in the laboratory. During the test, the axial force on each point monitored on the bolt was recorded by a strain gauge, and the attenuation trend of the strain was studied. An analytical model that considers the inhibition of the bolt rail effect due to an increase in the normal stress was proposed to predict the shear mechanical behaviour of rock bolted joints. The new model accommodates the bolt shear behaviours in the elastic stage and plastic stage, and the estimated values agree well with the results of the direct shear tests in the laboratory. The validation shows that the proposed model can effectively describe the deformation characteristics of the bolts in the shear tests.

摘要

锚杆被广泛应用与边坡岩体的加固。由于影响锚杆轴力和剪力的因素过于复杂, 因此, 建立锚 固节理剪切力学分析模型十分困难。锚杆在剪切作用下表现出导轨效应, 即岩体会沿着像轨道一样的 锚杆滑动。节理面的法向应力可以抑制导轨效应, 从而降低锚杆中的轴力的发挥, 然而, 现有的分析 模型没有考虑到这一影响因素。为了研究法向应力对锚杆导轨效应影响, 开展不同法向应力下的锚固 节理剪切试验, 采用应变片记录锚杆各监测点的轴向应变, 研究了锚杆轴力随法向应力增大而衰减的 规律。基于轴力的衰减规律, 提出了一种考虑法向应力对锚杆轨道效应抑制作用的锚固节理剪切力学 分析模型, 该模型兼顾了锚杆弹性阶段和塑性阶段的剪切特性, 可以较好地预测锚固节理的剪切力学 行为。模型预测值与室内直剪试验结果吻合较好。验证表明, 该模型能有效地描述锚杆在剪切试验中 的变形特性。