深圳地铁12号线沙三站采用新型上下组合式矩形顶管机进行建造,目前对于该形式顶管机的排渣速率及上下排渣速率的组合方式对掘进过程中地层的力学响应影响缺乏研究。建立该顶管机的等尺寸模型,利用离散元法研究了不同排渣速率大小和上下子顶管机不同排渣速率差对地表沉降和开挖面稳定性的影响规律。结果表明:最佳螺机转速为95 rpm(对应的排渣-顶进速度比为9~10 r/mm),该转速下不会发生超排或滞排,对地表沉降影响最小;大于95 rpm转速为超排情况,可导致开挖面局部失稳,最终导致地表坍塌,小于95 rpm转速为滞排情况,可导致地表隆起;相对于上下子顶管机排渣速率差异引起的地表最大位移(3 cm),全开挖面不同排渣速率对地表沉降的影响更显著,所引起的地表位移在-10 cm(沉降)到16 cm(隆起)范围内;总结了浅埋矩形顶管施工开挖面局部失稳破坏的演化规律,分为非满仓局部失稳、局部失稳发展,以及贯通地表破坏三个发展阶段。研究成果可为相关工程提供理论参考。
An innovative rectangular pipe-jacking machine in the form of up-and-down combination is employed in the construction of Shasan station in Shenzhen Rail Transit Line 12. However, existing studies fall short of investigation into the effect on the mechanical responses of stratum caused by the rate of muck discharge and its up and down combination modes. Therefore, this research establishes a full-scale model of this machine and uses Discrete Element Method to investigate the effects produced by different muck discharge rates and the differences in discharge rates between the upper and lower submachines. The results show that: The optimal rotation speed of screw conveyors for tunneling is 95 rpm (which corresponds to the ratio of muck discharge-to-driving rate is 9~10 r/mm), under which no excess or under discharge will occur, and the influence on vertical displacement of ground surface can be minimal. The excess discharge is that the rate higher than that, which can lead to local failure on tunneling face and ultimately ground collapse, while the under discharge is that the rate lower than that, which can induce ground uplift. Compared with the maximum displacement (3 cm) induced by the rate differences between the upper and lower submachines the muck discharge rate of the whole tunneling face can influence ground subsidence more significantly, which ranges from -10 cm (settlement) to 16 cm (uplift). Additionally, the study summarized the progressing regulation of local failure on tunneling face regarding rectangular pipe-jacking constructions under a shallow cover, which can be divided into three steps: underfilled muck chamber causing local failure, local failure developing, and failure penetrating to surface with ground collapsing. Grounded in the results obtained, this study is expected to serve correlative engineering projects with theoretical reference.
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