A Study On Construction Technologies Of Shield Tunnel Crossing Complex Buildings

Based on the shield tunneling underpassing Bihai Garden on Shenzhen Subway Line 5, this study investigated the behavior of ground settlement, displacement of building pile foundation, mechanical characteristics of segment linings, as well as control technology of shield driving due to shield tunneling, by using a combined method of literature review, theoretical analysis, numerical simulation, field construction assort and field segment tests. The achievement obtained from the study can be used to reduce the impact of shield tunneling on buildings, and to provide an important reference to the metro projects in the future. The main research work and achievements are as follows:(1) By carrying out numerical modeling of shield tunneling process of underpassing buildings, the study analyzed the pattern of groud settlement and facors affecting the surface settlement. The surface settlement is closely related to tunnling parameters. Appropriately increasing soil storage pressure and grouting pressure can effectively control ground settlement, but the pressure value should not be too large, otherwise it could easily lead to surface uplift.(2) The analysis of monitoring data showed that the surface settlement of cross-section is close to the normal distribution, the maximum subsidence occurs on the tunnel axis. Affected area of cross-sectional settlement and vertical section are respectively about twice and triple the tunnel diameter. Ground settlement monitoring results are consistent with the numerical results. The upside building will produce horizontal displacement except for vertical displacement, by the reason of irregular disturbances and partial load when shield excavating, but compared to the vertical displacement, the value of horizontal displacement is just about one third vertical displacement.(3) After the shield tunneling started, the tunnel arch subsides while the tunnel bottom upsides. With the continuous advance of shield, the deformation of assembled segments becomes more and more obvious. When the segment coming out of the shield tail, the surface settlment increases suddenly and settlement rate reaches its maximum. So the deformation control when the segment coming out of the shield tail is the key to control ground settlement in shield tunneling. (4) Based on the processing and analysis of construction data, a set of control parameters of shield tunneling beneath the buildings were summarized. Before the tunneling, the shield machine equipment must be checked and repaired carefully, and an emergency plan would be made, the construction would be in accordance with the principle of "safe, fast, continuous". It would reasonably control tunneling parameters, an extra 0.2 Bar of earth chamber pressure would be given based on the calculation, it would strictly control the unearth amount, reduce the amount of over excavation and reasonably make deviation rectification in order to reduce disturbance to soil, surface displacement and ground loss; it would strictly control the amount of synchronized grouting and grouting pressure, grouting volume is generally six cubic per ring; it would enhance sediment improving to has a good plastic and to reduce friction loss of the tool furthermore extending tool life.(5) When the geological condition is poor, to ensure the safety of the building, the support layer of pile and foundation must be prereinforced or reinforced. While shield machine is excavating beneath the building, the frequency of monitoring must be increased, the monitoring results must be timely feedbacked to the construction and used to adjust the construction parameters, which can prevent ground from too large or too fast settlement.(6) In the process of shield tunneling, there are two type of measures to avoid occurrence of settlment, tilt, even structural damage, including active control and passive control. The active control is optimizing construction parameters to reduce the adverse effect on buildings through the construction source. The passive control is, however, protecting the surrounding buildings by adopting partition, underpinning, soil stabilization and other methods. The active control should be focused on in the protection of nearby buildings along the tunnel.