Construction Technology Of Large Diameter Slurry Balance Shield Going Through The Floodplain Silty Sand Strata Of Xiangjiang River

Changsha Nanhu road tunnel is the first slurry-shield tunnel underpassing the Xiangjiang River, which means that the construction experiences is short. When driving across the flood plain of west side of Xiangjiang River, the strata above the tunnel is silty sand and sandy gravel layer, with massive underwater, high seepage coefficient, loose strata and poor self-supporting ability. When driving the north tunnel at this stratum firstly, ground subsidence had happened. Based on the study of silty sand strata, this paper have analyzed the reason of ground subsidence, and then proposed some control measures for the next tunnel of south. The main research contents as follows:(1) Take some samples from silty sand strata to do laboratory tests. The main tests as follows:specific gravity test, grain-size analysis, void ratio test, direct shear test, triaxial compression test. Through these tests, we can get the physical and mechanics parameters and engineering characters of silty sand, which provide the basis for the ground subsidence analysis and the control measures.(2) Analyzed form the aspects of strata characters, advancing mode and driving parameters and pore water pressure fluctuation, we try to find the reasons of ground subsidence in flood plain at west side of Xiangjiang River, and then proposal some control measures.(3) Have introduced the method of high-pressure rotary jet grouting pile to reinforce the ground, and then analyzed the advancing mode and driving parameters between north and south tunnel driving, to verify the effectiveness of such control measures when crossing the silty sand strata.