不等跨连拱铁路隧道围岩压力分布及受力特征模型试验研究

Model test study of surrounding rock pressure distribution and mechanical characteristics of unequal-span double-arch railway tunnel

以兰渝铁路新作坊隧道洞口明挖段不等跨连拱结构为背景,采用室内模型试验的方法,对不等跨连拱铁路隧道围岩压力分布及受力特征进行研究。试验结果表明：隧道水平侧压力均小于竖向围岩压力,拱顶处侧压力小于墙脚处侧压力,小洞侧侧压力系数平均为0.55,大洞侧侧压力系数平均为0.65;中隔墙顶部围岩压力均大于拱顶处围岩压力,且大洞拱顶围岩压力约为小洞的1.2倍;隧道结构总体为小偏心压弯构件,大洞所承受的轴力总体比小洞承受的轴力大20%-30%;隧道先后在大小洞靠近中隔墙的拱腰及仰拱处破坏,最终发生整体失稳;靠近中隔墙的大小洞拱腰及仰拱是设计施工时应重点关注的部位;最终获得不等跨连拱铁路隧道的围岩压力分布模式,研究结果可以直接指导新作坊隧道结构的设计与施工,有利于完善不等跨连拱隧道设计施工理念。

A model test is carried out to study the distribution of surrounding rock pressure and its mechanical characteristics based on open excavation section of Xinzuofang unequal-span double-arch tunnel of Lanzhou-Chongqing railway. Test results show that lateral pressure acting on the tunnel is smaller than the vertical stress of surrounding rock, and lateral pressure at the crown is smaller than that at the bottom of side wall, moreover, lateral pressure coefficient of small hole side is about 0.55 on average, while the big hole side is about 0.65. The stress of surrounding rock on the top of middle wall is bigger than that on the crown; the surrounding rock stress of big hole side is about 1.2 times that of the small hole. The tunnel is in a small eccentric bending state, and thrust stress in big hole is about 20% to 30% greater than that in small hole side; the destroy of tunnel structure firstly occurs at hance and invert near the middle wall in succession, finally the whole structure collapse; thus, the hance and invert near the middle wall are the place that should be focused on in the design and construction. Based on the above, the mode of surrounding rock pressure distribution is obtained finally. The results can directly provide guidance for the design and construction of Xinzuofang tunnel; what’s more, it’s also helpful to improving the design and construction concepts related to the unequal-span double-arch tunnel.