软弱围岩隧道锁脚锚杆受力特性及其力学计算模型

锁脚锚杆在软弱围岩隧道中应用非常广泛，为了研究其受力特性，以包茂线西康高速公路包家山特长公路隧道为依托，采用现场试验的方法，对典型断面锚杆轴向应力进行测试，结果表明：拱部锚杆受力较小，最大应力仅为锚杆极限应力的11.5%，作用不大；锁脚锚杆受力较大，最大应力达到锚杆极限应力的55.4%，作用很大；锁脚锚杆受长度和角度限制，不能发挥锚固作用。在分析其受力特性的基础上，采用结构力学和弹性地基梁的方法，建立了钢架和锁脚锚杆力学计算模型。应用该模型对隧道测试断面处的锁脚锚杆受力进行了分析计算，给出了锁脚锚杆弯矩分布图。根据弯矩推算锚杆应变值，并与实测值进行对比，结果表明：实测值和计算值规律一致，在距离孔口最近位置处锚杆应变最大，随着距离孔口距离增大，应变逐渐变小。

Mechanical characteristics and mechanical calculation model of tunnel feet-lock bolt in weak surrounding rock

The feet-lock bolt is widely used in weak surrounding rock tunnel. In order to study the mechanical characteristics, based on the Baojiashan extra-long highway tunnel in Baomao line Xikang highway, the field test method was used to test the bolt axial stress at the typical section. The results show that the stress of arch department bolts is small, the maximum stress is only 11.5% of the bolt’s ultimate stress and the effect is not big; the stress of feet-lock bolts is larger, the maximum stress is 55.4% of the bolt’s ultimate stress and the effect is very big; and the anchorage effect cannot be used very much at the feet-lock bolts as a result of the length and the angle limitations. Based on the analysis of its mechanical characteristic, the mechanical calculation model of the steel frame and feet-lock bolt is established using structural mechanical and elastic foundation beam methods. And the model is used to analyze the stress of feet-lock bolts at the tunnel test section, and the bending moment distribution of feet-lock bolt is given. The strain value of bolt is calculated from the bending moment and compared with measured values. The results show that the calculated values are consistent with the measured ones, that the strain of bolt is the largest at the closest point to the orifice and that the strain decreases gradually with the increasing distance between orifice and anchor body.