Abstract：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.
