Abstract:

Based on the running tunnel (JinmasiTaipingcun) on Kunming Metro line No. 3, the intermediate pilot method is adopted for the large crosssection rectangular tunnel in soft soil stratum. The mechanical characteristics of tunnel structure are monitored and analyzed by field monitoring method combining with construction theory during tunnel construction. The results show that the internal force of tunnel primary support is in a stable range under the condition of long pipe roofing grouting at roof and bilateral sides. And the axial force of primary support is in a tension state at the bottom of pilot tunnel due to the excavation disturbance of different pilot tunnels, especially the construction process management should be strengthened during the construction of the second, fourth and fifth pilot tunnel. The maximum stress between surrounding rock and structure appears at the bottom of pilot tunnel. And the stresses of four corners of rectangular structure are obviously more than those of other parts of tunnel structure, which shows that the grouting measure should be adopted so as to improve the bearing capacity of tunnel foundation. Based on the analysis of the stress change law of temporary support, the stress of temporary structure appears in an updown change state caused by the construction process of different pilot tunnels, which reflects the stress releasing characteristics of surrounding rock for all pilot tunnels. The results can provide reference for the design, construction and monitoring of shallowburied rectangular tunnel in soft soil stratum.

Key words: soft soil stratum, large crosssection rectangular tunnel, intermediate pilot method, construction mechanics, monitoring