Analysis Of Ground Settlement And Grouting Reinforcement For Cross-river Larger-diameter Shield Tunneling Construction

With the dramatic development of underground transportation in China, shield tunneling construction has become main stream in metro construction. The construction of large-diameter shield will have certain impact on ground stability, even greatly affect ground settlement. It is significant to analyze the influencing rules of ground settlement especially exerted by the construction of large-diameter shield. Taking the ground settlement change law as main research target, based on the three-dimensional finite element numerical simulation method, the paper will illustrate the influencing law of ground settlement conducted by major influencing factors in large-diameter shield construction. Furthermore, combined with practical engineering, the paper will analyze the reinforcement effect of stratum grouting rendered by large-diameter shield tunneling. General structure of this paper is as followed:Firstly, this paper reviewed and summarized related literature to analyze the disturbance process of formation affected by the shield tunneling and deformation factors. By establishing three-dimensional finite element numerical model, the paper focused on selecting and analyzing the primary influencing factors to surface in the shield tunneling construction and summarized the influencing law of ground settlement affected by influencing factors.Taking Tianjin rail underground transit line across Haihe river as example, three formulas for tunneling minimal thickness of overburden layer were deduced based on theoretical derivation. By setting up three-dimensional finite element numerical model, this paper numerically simulated shield tunneling construction across the Haihe River bottom, with the research emphasis on the comparative analysis of river bottom surface settlement under grouting and without grouting. Wireless monitoring information management and early warning system was used for real-time monitoring the river bottom surface settlement during the construction of shield tunneling, furthermore, carried out comparison between it and numerical simulation result.The analysis indicates that factors such as physical property of soil (soil elastic module, internal friction angel, cohesion), heading face supporting force, excavation drawing pace, buried depth have significant impact on ground settlement in light of obvious deformation law. Such conclusions are drawn to provide corresponding guidance for subsequent projects. It is proved by the formulas of tunneling minimal thickness of overburden layer that measures should be taken to ensure safety once thickness of overburden cannot meet the requirements of project. Numerical analysis shows that shield tunneling construction imposes too much extent of ground settlement when crossing river bottom without grouting, comparably, grouting reinforcement is strikingly effective in lowering the extent of ground settlement. By Comparing, numerical simulation analysis is in line with the field monitoring data, which further proves the validity of the model and the parameters selection, moreover, it factually reflects the whole process of shield tunneling construction crossing Haihe River and provides certain references for the prediction of subsequent projects.