卵砾石土层大跨公路隧道初期支护优化研究

 江苏省宁常高速公路茅山隧道位于卵砾石土层斜坡中，具有浅埋、大跨扁平的特点，结合现场大型剪切试验分析、获取卵砾石层剪切强度参数，采用弹塑性非线性有限元法模拟并分析开挖和支护的全过程。根据新奥法，喷混凝土是公路隧道施工中体现初期支护柔性支护特点的主要因素之一，针对卵砾石土层II类软弱围岩浅埋地段交叉中隔壁法实际施工工艺特点，选择拱顶区右上部、中轴线、左上部3个测点下沉值(S1，S2，S3)建立协方差函数，并结合围岩和二衬塑性区的分析，对初支喷混凝土厚度进行合理性研究，提出该隧道卵砾石土层拱顶埋深在26 m左右断面最合理的初支喷混凝土厚度为22～28 cm，该典型断面最优初支喷混凝土厚度为26 cm，该研究成果对斜坡浅埋软弱II类围岩地段交叉中隔壁法施工设计有一定参考价值

PRIMARY-SUPPORTING OPTIMIZATION FOR LARGE-SPAN ROAD TUNNELS IN GRAVEL DEPOSIT LAYERS

Maoshan road tunnel in southern area of Jiangsu Province，located in slope of gravel deposits layers，has the characteristics of large span，shallow overburden. With the parameters of shear strength of gravel deposits obtained from the large in-situ shear test analysis，numerical simulation is conducted to analyze the excavating and supporting processes of the tunnel with elastoplastic FEM. According to NATM，in the process of tunnel construction，polypropylene fibre shotcrete is the main factor embodying the feature of primary-support flexible support. Based on the research on the center cross-diagram(CRD) method construction process applied to shallow-buried tunnels in soft surrounding rock class II，and the analysis of the covariance function of measured deformations of three points：right-upper point(S1)，top(S2)，and left-upper point(S3) and the plastic zone of surrounding rock and inner lining，a research on the rationality of primary-supporting thickness is performed. And it is proposed that the most rational thickness of polypropylene fibre shotcrete is 22–28 cm for the tunnel with buried depth of 26 m. The optimum thickness of polypropylene fibre shotcrete for the typical section of the tunnel is 26 cm. This research result，in addition to the method，can be used as reference in the construction and design of CRD method in slope and shallow-buried tunnels in soft surrounding rock class II.