Development of the safety control framework for shield tunneling in close proximity to the operational subway tunnels: case studies in mainland China
IntroductionChina’s largest cities like Beijing and Shanghai have seen a sharp increase in subway network development as a result of the rapid urbanization in the last decade. The cities are still expanding their subway networks now, and many shield tunnels are being or will be constructed in close proximity to the existing operational subway tunnels. The execution plans for the new nearby shield tunnel construction calls for the development of a safety control framework—a set of control standards and best practices to help organizations manage the risks involved.Case description Typical case studies and relevant key technical parameters are presented with a view to presenting the resulting safety control framework. The framework, created through collaboration among the relevant parties, addresses and manages the risks in a systematic way based on actual conditions of each tunnel crossing construction. The framework consists of six parts: (1) inspecting the operational subway tunnels; (2) deciding allowed movements of the existing tunnels and tracks; (3) simulating effects of the shield tunneling on the existing tunnels; (4) doing preparation work; (5) monitoring design and information management; and (6) measures and activation mechanism of the countermeasures. The six components are explained and demonstrated in detail.Discussion and EvaluationIn the end, discussions made involve construction and post-construction settlement of the operational tunnel, application of the remedial grouting to rectify excessive settlements of the operational tunnel, and use of the innovative tool of the optical fiber measurement for tunnel movement monitoring.ConclusionsIt is concluded that the construction movement of the tunnel can be controlled within 15 mm when the shield machine is <7 m in excavation diameter. The post-construction settlement of the tunnel buried in the very soft ground is much greater than its construction settlement, and last several years until reaching a final stable state. Two cases are outlined to demonstrate the feasibility of using the remedial grouting to reduce the long-term settlement of the operational tunnels. The more and more segmental tunnels being constructed, there is an increasing need of the optical fiber measurement for tunnel movement monitoring in the near future.
Research on the Mechanical Behaviors of New Tunnel Construction in the Area Orthogonal to Existing Metro Tunnel
Research purposes: For construction of No 3 line's shield tunnel under-passing the existed No 1 line's tunnel of Shanghai metro,the mechanical behaviors of new tunnel construction were simulated with the three-dimensional fast Lagrangian analysis of continua(FLAC3D)method,the change and influencing scope of stratum stresses and the stresses and safety of structure were discussed,and the measures for and proposals to ensuring the construction safety of new tunnel and operation safety of existing tunnel were offered.Research conclusions:The additional stresses distribution of existing tunnel was of laterally symmetrical status which took the central line of new tunnel as symmetry axis in construction process.The subsidence of the existing tunnel occurred and additional stresses of existing tunnel increased during construction of new tunnel.As the maximum internal force in the target face of the tunnel tubular lining appeared on the tubular lining on the arch web on both sides of new tunnel,the stratum between tunnels should be reinforced.When construction was finished,the main stress in the target face of the tubular lining of the shield tunnel became the biggest.
Twin Tunnel Interaction: Surface and Subsurface Effects
ABSTRACT This article presents the results from 13 plane strain, coupled consolidation, non-linear finite element analyses of twin tunnel construction. There are two sets of analyses, the first models two tunnels running parallel side-by-side, and the second one above the other (piggyback). The spacing between the tunnels is varied so as to ascertain the zones of influence, and the time between the construction of the two tunnels is varied to establish the influence of prolonged consolidation or swelling. The results present the expected modification to the settlement profile above the second of two close tunnel excavations, and the expected distortion induced in an existing tunnel lining when an adjacent tunnel is excavated. Field data, where available, are presented to support the magnitudes of the interactions being predicted numerically. It is concluded that the relative position (above, below, or to the side) and the physical spacing of the tunnels has a significant effect on the surface settlement p...