基于岩体等级和隧道跨度耦合影响的卸荷拱研究

Research on Unloading Arch Based on Coupling Influence of Rock Mass Degree and Tunnel Span

以直墙拱顶隧道为模型,取隧道顶部至地表路径为分析对象,通过路径上最大主应力曲线判定出卸荷拱内、外边界点,从而可以确定岩体中卸荷拱的范围;在此基础上,分析了隧道拱顶矢高对卸荷拱的影响情况,研究了岩体等级及隧道跨度对卸荷拱内、外边界点及临界成拱埋深的耦合影响规律。结果表明:对于直墙拱顶隧道,当隧道拱顶高跨比小于0.5时,拱顶矢高的变化对卸荷拱基本无影响;卸荷拱内边界点至隧道顶部距离随岩体等级的提高、隧道跨度的增大而增大;外边界点至隧道顶部距离随岩体等级的提高而减小,随隧道跨度的增大而增大;临界成拱埋深基本不受岩体等级的影响,但随隧道跨度的增大而增大;拟合得到了内、外边界点及临界成拱埋深的计算公式;通过该计算公式可以判断出隧道上部岩体中卸荷拱的范围,卸荷拱拱体厚度为卸荷拱区域岩体厚度的1/3,且随岩体等级的提高而减小,随隧道跨度的增大而增大。所得结论可为岩体地下工程的设计施工提供参考。

Taking the upright wall-arched ceiling tunnel as the analytical model, and taking the road from the tunnel roof to the ground as the analytical object, the internal and external boundary points could be found out through the maximum principal stress diagram. On this foundation, the influence of the tunnel＇s arch ceiling height on the unloading arch was researched, the arching regulation and the critical arching depth of the unloading arch under the coupling influence of the rock mass degree and the tunnel span were studied. The results show that when the height-to-span ratio of the tunnel＇s arch ceiling is smaller than 0.5, the change of the tunnel＇s arch ceiling height has little influence on the unloading arch. The distance from the internal boundary point to the roof of the tunnel＇s arch ceiling is becoming longer with the raising of the rock mass degree and the lengthening of the tunnel span. The distance from the external boundary point to the roof of the tunnel＇s arch ceiling is becoming shorter with the raising of the rock mass degree, but longer with the lengthening of the tunnel span. The critical arching depth is becoming deeper with the lengthening of the tunnel span, but changeless with variation of the rock mass degree. The calculation formulae of the internal and external boundary points and the critical arching depth are obtained. Through the calculation formulae, the area of the unloading arch in the rock mass can be identified, and it can be concluded that the unloading arch body＇s thickness is 1/3 of the unloading arch region＇s thickness. The unloading arch body＇s thickness is becoming thinner with the raising of the rock mass degree, but thicker with the lengthening of the tunnel span. The conclusions can provide reference for the underground rock mass engineering＇s design and construction.