粉细砂地层双线盾构施工实测地表沉降规律分析与预测

依托南通地铁二号线某区间盾构隧道施工，针对盾构穿越典型粉细砂地层条件，对双线盾构隧道施工引起的地表沉降开展现场测试和规律分析，对经典Peck公式在南通地区粉细砂地层中双线盾构施工的适用性进行探讨，并研究先行线和后行线土体损失率和地表沉降槽宽度系数的取值及影响因素。研究结果表明，在粉细砂地层中，后行线隧道施工对地层的二次扰动效应会引起先行线轴线上方地表沉降的显著增加，且二次扰动效应明显强于其他软土地层，但弱于砂土地层；相较于淤泥质土地层，在粉细砂地层中盾构停机对地表沉降的影响更为显著；先行线和后行线施工引起土体损失率比值η₁/η₂在1~5倍范围内，平均值为2.3，先行线和后行线地表沉降槽宽度系数比值K₁/K₂在1~2倍范围内，平均值为1.4；砂土、粉细砂和粉土地层中土体损失率比值η₁/η₂均大于1，η₁/η₂和K₁/K₂与隧道覆土深度比（H/D）相关性较弱。

Investigation of surface settlement induced by twin shield tunelling in silty fine sand stratum

Field tests were carried out to observe surface settlement induced by twin shield construction in silty fine sand stratum, based on the project of Nantong Metro line 2. The applicability of the twin peck formula for silty fine sand stratum is examined through measured data. The ground loss rate, the width of the preceding tunnel and the rear tunnel were analyzed. The results show that in silty fine sand soil, the secondary perturbation effect of tunnel construction on the rear tunnel induces a significant increase in surface settlement above the axis of the preceding tunnel. The secondary perturbation effect in silty fine sand stratum is more obvious than that in other soft soil layers, but less than that for sand layer. Compared with silty soil layer, the impact of shield stoppage on ground settlement is more significant in silty fine sand stratum. The ratio of ground loss rate η₁/η₂ caused by the twin shield construction ranges from 1 to 5 with a mean value of 2.3, and the ratio of the surface settlement trough width parameter K₁/K₂ between the leading tunnel and the trailing tunnel ranges from 1 to 2 with a mean value of 1.4; The ratios of ground loss rate η₁/η₂ in sand, silty fine sand, and silt soil stratums all exceed 1. Furthermore, none obvious relationship can be found between ratios of ground loss rate η₁/η₂, width parameter K₁/K₂ and the ratio of cover depth to diameter (H/D).