软岩隧洞锁脚锚杆–钢拱架联合承载分析

JOINT BEARING ANALYSIS FOR FEET-LOCK BOLT AND STEEL ARCH IN WEAK ROCK TUNNEL

锁脚锚杆–钢拱架联合支护是控制隧洞拱顶下沉的有效措施。为了研究其承载机制,建立软岩隧洞锁脚锚杆–钢拱架联合承载的力学计算模型,考虑钢拱架与锁脚锚杆连接处的弯矩、轴力、剪力传递及变形协调。将钢拱架处理为弹性固定无铰拱,采用结构力学法进行求解。锁脚锚杆的横向效应和轴向效应分析表达式分别采用弹性地基梁法和荷载传递法进行详细推导。通过实例首先研究锁脚锚杆的内力与变形特性,并与未考虑弯矩传递及变形协调的已有文献中的模型结果进行对比,然后讨论不同打设角度对锁脚锚杆与钢拱架连接处的内力和变形的影响,最后应用该模型对比分析围岩侧压力系数、刚度以及锁脚锚杆各参数对控制隧洞拱顶下沉效果的影响规律。得出以下结论:锁脚锚杆最不利受力位置在与钢拱架焊接的部位,该部位应焊接牢固,并且在计算模型中宜考虑焊接部位的弯矩传递;锁脚锚杆横向效应主要集中在端部附近区域,该区域围岩应重点加固,且锚杆过长对发挥其横向作用并无贡献;其打设角度不宜过大,取45°左右为佳;增大单根锁脚锚杆(管)规格或增加数量,可获得更好的支护效果;设计中,围岩侧压力系数宜考虑较小值。

Combined structure of feet-lock bolt and steel arch is an effective support measure in preventing the crown settlement. An analytical model to calculate the support of joint bearing with feet-lock bolt and steel arch in weak rock tunnel was established considering the compatibility conditions of bending moment, axial force, shear force and deformations at the junction. The steel arch was taken as a fixed arch and was analyzed using the method of structural mechanics. The formulae describing the lateral and axial mechanical behaviors of feet-lock bolt were derived with the methods of elastic foundation beam and load transfer respectively. The internal forces and the deformation of feet-lock bolt were studied through an example, and the results were compared with the model given in a reference paper in which the bending moment and deformation compatibility conditions at the junction were ignored. The influence of different installation angles of feet-lock bolt on its internal force and deformations at the junction was discussed. Finally, the influencing factors for the effect in controlling the crown subsidence were studied, including the lateral pressure coefficient and stiffness of surrounding rock, and the parameters of feet-lock bolt. The results indicated that the welded part was the weakest link for feet-lock bolt and should be welded firmly. The bending moment transfer at the junction was recommended to be considered. The lateral resistance to bolt mainly concentrated in the region near the end of bolt, where the surrounding rock should be specially reinforced. Extra length of bolt had no effect to its lateral behavior. The best installation angle was found to be about 45°.: Using more feet-lock bolt(pipe) or using feet-lock bolt(pipe) of high specification enhanced support effect. A low value of the lateral pressure coefficient of surrounding rock be better considered in the design of feet-lock bolt. ©, 2015, Academia Sinica. All right reserved.