深埋圆形隧道的压力拱研究

Study on Pressure-Arch of Deep Circular Tunnel

针对压力拱存在概念不明确的问题,阐述了隧道中压力拱的概念,指出压力拱是一条受压的曲线,隧道开挖后会形成一次开挖压力拱,当围岩出现拉应力时会导致二次开挖压力拱出现。然后,在现有深埋圆形隧道解析解基础上,将地应力分为静水压力、双向常应力、与深度成正比三种情况进行压力拱分析。研究结果表明:对于地应力为静水压力情况,一次压力拱和隧道的轮廓线重合;对于地应力为双向常应力情况,一次压力拱和水平与竖向应力比有关,还和受拉判断标准有关,当竖向应力是水平应力的3倍以上时,拱顶将产生拉应力,且压力拱和隧道轮廓线间的受拉体随其值的增大而增大;对于地应力与深度成正比情况,一次压力拱的特性和地应力为双向常应力情况类似,隧道顶部受拉时的水平地应力与竖向地应力比值要小于0.2。从工程安全角度考虑,压力拱宜以最小主应力受拉为判断标准。

According to the problem that the conception of pressure-arch is undefined, the conception of pres- sure-arch in tunnel is described. It is pointed out that the pressure-arch is a compressive curve. First pressure-arch can be formed when tunnel is excavated. The first pressure-arch will result in the secondary pressure-arch when the surrounding rock generated tension stress. Then, according to the existing analytic stress solution of deep circular tun- nel, the ground stress is classified into three cases to analyze the pressure-arch. Firstly, the ground stress is a hydro- static-pressure, the first pressure-arch is the contour of circular tunnel. Secondly, the ground stress is bidirectional constant, the first pressure-arch is related not only to the initial stress ratio between horizontal and vertical stresses but also to the tension stress criterion. Tensile stress will occur in vault of the tunnel when initial stress ratio between ver- tical and horizontal stresses is more than three. Tension area between pressure-arch and the contour of circular tunnel increases with initial stress ratio between vertical and horizontal ones. Thirdly, when the ground stress is proportional to the depth, the characteristic of first pressure-arch is similar to that in second case. Tensile stress will occur in vault of the tunnel when initial stress ratio between horizontal and vertical ones is less than 0.2. Considering the engineer- ing safety, for the judging criterion the minimum principal stress in tension should be selected to analyze the pressure- arch.