北京地铁砂卵石地层盾构推力组成及可控因素敏感性研究

A Study of the Composition of the Shield Thrust and the Sensitivity of Controllable Factors Concerning the Beijing Metro in a Sandy Cobble Stratum

北京地铁盾构施工中穿越的砂卵石地层卵石含量高、粒径大，土体摩阻力大、流塑性差，给施工过程中盾构推力的控制带来了极大困难。为了降低盾构施工风险、提高掘进效率，文章着重在土压平衡盾构推力组成特征及主要可控因素等方面展开细致的研究；系统分析了土压平衡盾构掘进机理，推导了盾构推力的理论计算公式。根据砂卵石地层的力学特征，分析了砂卵石地层盾构推力的组成特征，并推导了简化的盾构推力计算公式。为了检验理论计算公式的合理性，以推导的盾构推力为研究对象，对刀盘开口率及碴土内摩擦角两大可控因素进行了敏感性统计分析。研究结果表明：（1）盾构推力与刀盘开口率成反比，刀盘开口率每增加10％，盾构推力约降低3％～5％；（2）盾构推力与碴土的内摩擦角成正比，内摩擦角每增加10。，盾构推力约增加6％～10％。同时以北京地铁十号线二期盾构工程为背景，开展盾构现场掘进试验，对理论研究成果进行了验证。研究成果为类似砂卵石地层盾构选型、设计与工程施工阶段土压平衡盾构推力的预测与控制提供依据，具有一定的理论意义与应用价值。

The sandy cobble stratum encountered by the Beijing metro project is characterized by a high content of large cobbles, great friction resistance, and a low plastic flow of the soil body, all of which caused many difficulties regarding the control of the shield thrust during tunnel construction. To lower the risk and increase efficiency, a careful study of the characteristics of thrust compositions and controllable factors of the EPB shield was carried out, a systematical analysis of the mechanism of the EPB shield driver was undertaken, and a formula for theoretical shield thrust calculations was deduced. The composition characteristics of a shield thrust in a sandy cobble stratum were analyzed and a simplified formula was derived according to the mechanical characteristics of the sandy cobble stratum. To demonstrate the rationality of the theoretical formula, a sensitivity statistical analysis with the derived shield thrust as a study object was carried out regarding the two controllable factors of open ratio of the cutter head and internal friction angle of the muck. The results show that： 1） the shield thrust is inversely proportional to the open ratio of the cutter head with an increase of the open ratio by 10%, resulting in a reduction of the shield thrust by about 3-5%; and 2） the shield thrust is proportional to the internal friction angle of the muck with an increase of the internal friction angle by 10＂, resulting in an increase of the shield thrust by about 6-10%. The research results were verified by the on-site shield driving test during the phase 2 project of the Beijing Metro line 10. This study can be used as a reference for similar projects in terms of shied selection, thrust prediction, and control measures.