软土层中类矩形盾构掘进施工引起地层竖向变形实测与分析

 类矩形盾构断面形状、机械配置与圆形盾构的差异必然引起地层变形规律有所不同，以国内首例软土层中类矩形盾构地铁隧道工程为背景，依据现场实测地表变形、土体分层沉降数据，分析类矩形盾构隧道施工引起地层竖向变形的基本规律，并结合变形机制对施工控制提出建议。结果表明：类矩形盾构施工引起地表沉降最大值约50 mm，开挖面前方影响范围约20 m；地表竖向位移随时间发展呈现出缓慢沉降(隆起)、急剧隆起、快速沉降、平稳沉降4个阶段，沉降主要发生在盾构通过后，由软土地层受扰动后固结引起。地层竖向变形主要受土仓压力、盾尾注浆、盾构姿态等因素的影响，其中，盾构掘进姿态控制是盾构两侧土体竖向位移方向相反的主要原因，盾构姿态对周围地层变形影响比单圆盾构更显著。

Measurement and analysis of vertical deformation of stratum induced by quasi-rectangular shield tunneling in soft ground

The stratum deformation caused by the quasi-rectangular shield tunneling is different from the circular shield tunneling and the limited research has been carried out to study the issue. The first time application of the quasi-rectangular shield tunnel in soft ground in China was studied and the surface deformation and layered settlement were monitored and analyzed to investigate the major pattern of the vertical stratum deformation. The suggestions for the construction controlling were presented in terms of the deformation mechanism. The results show that the maximum surface settlement is about 50 mm and the range of excavation influence is about 20 m ahead of the excavation face. The vertical displacement of the ground surface experiences four stages over the tunneling period，the slowly down(upward) stage，the rapid upward stage，the rapid down stage and the gently down stage. The surface settlement occurs mainly after the pass of the shield tail，which is caused by the consolidation of the disturbed soft stratum. The main factors for the vertical stratum deformation include the chamber pressure，synchronous grouting and shield posture. The shield posture caused the soil on two sides of the shield machine to move in the opposite directions. In addition，the influence of the shield posture to soil deformation is more significant than in the case of single circle shield tunneling.