长锚杆/锚索改善深埋大跨度隧道初支结构受力试验研究

Experimental study on improving mechanical characteristics of initial support structure of deep buried large-span tunnels with long bolts or cables

针对深埋大跨度软岩隧道拱脚及拱顶处初支开裂、钢架变形过大问题,提出了局部增设长锚杆或锚索的支护技术,以实现对该类隧道初支结构受力的调节改善。基于课题组自主研发的隧道结构性能测试平台,对比分析了同等围岩荷载作用下系统锚杆支护与多类长锚杆/锚索支护方案的初期支护结构受力变形特征,研究了不同环向间距与布设范围的长锚杆/锚索支护效果。研究结果表明:(1)常规支护时,大跨度隧道初期支护整体呈压扁趋势,拱顶内侧与拱脚外侧承受结构最大弯矩而最先开裂,仰拱内侧拉裂后模型加速变形进而引起结构整体失稳破坏;(2)4种增设长锚杆或锚索支护方案下,初支拱顶处结构安全系数分别为常规支护体系的4.59,2.12,1.96,1.80倍,拱脚处结构安全系数分别为常规支护的5.23,2.80,2.34,2.37倍;(3)在拱部120°范围以2 m环向间距布设长锚杆对初支结构内力改善效果最佳,支护点轴向强拉力产生的局部负弯矩组合效应抵消了拱顶处较大正弯矩;(4)不同位置长锚杆/锚索支护力整体呈从拱顶处至拱肩侧先减小后增大的规律。

To address the issues of the initial cracking at the arch foot and crown and the excessive deformation of steel frames in deep-buried,large-span soft rock tunnels,a support technology involving localized addition of long anchor bolts or cables is proposed to adjust and improve the structural stress.Based on the tunnel structural performance testing platform independently developed by the authors,the stress and deformation characteristics of the initial support structures under the same surrounding rock loads are compared and analyzed between the system anchor support and multiple types of long anchor bolts or anchor cables deployment schemes.The effects of long bolts/cables support with different circumferential spacings and layout ranges are studied.The research results show that:(1)Under the conventional support,the initial support of a large-span tunnel under surrounding rock loads tends to flatten,with the inner side of the arch crown and the outer side of the arch foot bearing the maximum bending moment of the structures being the first to crack.After the inner side of the inverted arch cracks,the model accelerates deformation,leading to the overall instability and damage of the structures.(2)Under the four conditions of adding long anchor bolts or anchor cables for support,the structural safety factors at the initial support arch crown are 4.59 times,2.12 times,1.96 times and 1.80 times those of the conventional support system,and the structural safety factors at the arch toe are 5.23 times,2.80 times,2.34 times and 2.37 times those of the conventional support system,respectively.(3)Placing long anchor bolts at a circumferential distance of 2 m within 120°of the arch has the best effects on improving the internal force of the initially supported structures.The combined effects of local negative bending moments generated by the strong axial tension at the support points offset the larger positive bending moments at the arch crown.(4)The overall supporting force of long anchor bolts and anchor cables decreases first and then increases from the arch crown to the arch shoulder side.