Study On The Stress Of Supporting Structure And Surface Subsidence Of Shallow Embedded Tunnel In Watery And Weak Stratum

When shallow embedded tunnel is built in the watery and weak stratum,large deformation of surrounding rock even instability of tunnel may occur which will affect the ground surface and the surrounding environment. Taking a shallow embedded tunnel in the section from GDK25+080～GDK33+022.303 in the inter-city rail way from Dongguan to Huizhou, as the engineering background, the law of forces and deformation in the supporting structure and the subsidence of ground surface are studied. The research works and conclusions are as follows:(1) A kind of leak stoppage cement at the ratio of 1.0.8 with water was found to be used as shotcrete in model test.(2) The grouting and shotcrete equipment was improved and a kind of spray nozzle to jet shotcrete and a pressure grouting pipe was developed.(3) Two groups of model tests with/without advanced grouting of full section were carry out. The CD method was simulated in the excavation of tunnel. The internal of supporting structure and subsidence of surface ground were measured. Moreover, the model test was simulated by ABAQUS.The main conclusions are as follows:(1) When grouted with pressure 30 to 50kPa, the maximum surface uplift could reach up to 1.8mm, which is 45mm corresponding to the actual engineering and is much higher than 10mm which is the construction quality control standard.(2) The surface settlement curve shows the normal distribution curve described by Peck equation, and the maximum settlement point tends to the side of earlier excavation. The maximum surface settlement of model test is 2.6mm corresponding to 65mm in actual construction conditions. The maximum surface settlement of numerical simulation is 1.42mm corresponding to 35.5mm in actual construction conditions. They are all above the standard of 30mm set by construction quality control standard(3) It was found that most of ground surface subsidence (Model test is 83%, while numerical simulation is 79.4%) at measuring section takes place before the excavation reaches the section. The proportion of the subsidence during the excavation from 0D to 1D to the measuring section is as high as 63%. Therefore, to control the ground settlement, strong advanced support measures is quite necessary..(4) By measuring and calculating the internal force of the steel arch during the excavation of the tunnel, it was found that the vertical distance that affects the internal force of the arch during the excavation is about 1-2 times of the width of the tunnel. Before the removal of the diaphrgam, the side wall of arch bears larger axial force; Removal of the diaphrgam will cause large change of the stress state of the arch. When the diaphrgam is removed, the maximum bending moment appears in the arch corresponding to zone one and the zone four; the bending moment in zone two and zone three is smaller and appears to have a negative bending moment; the maximum axial force occurs in zone four, the axial force gets smaller in zone two and zone three and tensional axial force appears.