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Study on ground behaviour associated with tunneling in mixed-face soil condition

机译：混合面土条件下隧道掘进的地表特性研究

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摘要

The ground behaviour associated with tunnelling in mixed-faced soil condition is gaining more attention from researchers in recent years. A sudden change in soil medium at the tunnel face creates difficulties in controlling face pressure and over excavation that can cause substantial ground loss and movements. To date, a majority of studies were carried out in single-face soil conditions. Therefore, this research aims to understand the ground behaviour due to tunnelling in mixed-face soil conditions by local case studies and numerical analyses. Main studies include (i) ground behaviour at a tunnelling project (ii) 3-D FE study on the soil responses in single-face soil tunnelling of Old Alluvium (OA) and Kallang Formation (KF), and (iii) 3-D and 2-D FE study on the soil responses in mixed-face tunnelling.;The tunnel alignment of a recent tunnel project in Singapore was expected to pass through single-face and mixed-face soil conditions. With the measured field data, numerical back-analyses were performed to study mixed-face tunnelling behaviour using 3-D finite element (FE) GeoFEA software. The findings were compared with the well-understood behaviours of those in single layer tunnelling and similarities and differences were highlighted.;The FE studies demonstrated that the settlement increased up to 3.5 times at the mixed-face location, hard soil (OA) to soft soil (KF) in this case, as compared to single layer tunnelling in OA. Highly localised ground loss up to 2% was estimated. The longitudinal settlement profiles were highly dependent on the soil condition at the tunnel face and no longer followed the shape of cumulative Gaussian curve. However, the transverse settlement remained the same Gaussian profile as in single-face tunnelling.;A series of sensitivity studies were also implemented to investigate the influence of some important factors such as the contribution of F1 layer in the Kallang Formation, different face pressure values, tunnel advancing directions, and mixed-face tunnelling under different geological condition. The findings from parametric studies showed that the volume loss decreases with increasing face pressure, up to 1.25Hy (Hy = Hydrostatic pressure), beyond which reduction in the volume loss becomes insignificant. In order to maintain the volume loss less than 2% at all times, face pressure of 1.3Hy to 1.5Hy is recommended to maintain throughout the mixed soil transition zone. Sometimes, the face pressure is expressed in terms of the overburden pressure, P0 and the face pressure of 0.7P0 to 0.8P0, is recommended. Similar trends of mixed soil settlement were observed in different geologies for the same tunnel advancing direction. The relative stiffness of two different soils at the transition also influences the resulting ground movements. Soft clay and rock interface showed larger total settlement than that of hard soil and rock interface.;Finally, an idealization of mixed-face tunnelling problem in 2-D numerical analysis was discussed. The study showed that fairly reasonable predictions can be obtained with 2-D FE modelling, if the percentage of soft soil/hard soil at the tunnel face are correctly incorporated and the applied face pressure is 1.0Hy or higher.
机译：近年来，与混合面土条件下的隧道掘进相关的地面行为越来越受到研究人员的关注。隧道工作面土壤介质的突然变化给控制工作面压力和过度开挖带来了困难，可能导致大量的地面损失和运动。迄今为止，大多数研究都是在单面土壤条件下进行的。因此，本研究旨在通过局部案例研究和数值分析来了解由于混合面土条件下的隧道效应而引起的地表行为。主要研究包括（i）隧道工程的地面行为（ii）旧冲积层（OA）和加冷组（KF）单面土壤隧道中土壤响应的3-D FE研究，以及（iii）3-D混合面隧道施工中对土壤响应的二维有限元研究。；新加坡最近的一个隧道项目的隧道定线有望通过单面和混合面土壤条件。利用测得的现场数据，使用3-D有限元（FE）GeoFEA软件进行了数值反分析，以研究混合面隧穿行为。将研究结果与单层隧穿中的良好行为进行了比较，强调了相似性和差异。有限元研究表明，在混合面位置，硬土（OA）到软土的沉降量增加了3.5倍与OA中的单层隧穿相比，在这种情况下土壤（KF）更大。高度局部化的地面损失估计高达2％。纵向沉降曲线高度依赖于隧道工作面的土壤状况，不再遵循累积高斯曲线的形状。然而，横向沉降仍与单面隧穿中的高斯剖面保持一致。；还进行了一系列敏感性研究，以研究一些重要因素的影响，例如加冷组中F1层的贡献，不同的面压值，隧道前进方向和不同地质条件下的混合面隧道。参数研究的结果表明，体积损失随表面压力的增加而减小，最高可达1.25Hy（Hy =静水压力），超过此压力，体积损失的减少就变得微不足道。为了始终保持体积损失小于2％，建议在整个混合土壤过渡带中保持1.3Hy至1.5Hy的面压力。有时，面压力用上覆压力P0表示，建议使用0.7P0至0.8P0的面压力。对于相同的隧道行进方向，在不同的地质条件下观察到相似的混合土沉降趋势。过渡处两种不同土壤的相对刚度也会影响地面运动。软土和岩石界面的总沉降比硬土和岩石界面的总沉降要大。最后，讨论了二维数值分析中混合面隧道问题的理想化方法。研究表明，如果正确组合了隧道工作面的软土/硬土百分比，并且施加的工作面压力为1.0Hy或更高，则使用二维有限元建模可以获得相当合理的预测。

著录项

  • 作者

    Su, Thiri.;

  • 作者单位

    National University of Singapore (Singapore).;

  • 授予单位 National University of Singapore (Singapore).;
  • 学科 Environmental engineering.
  • 学位 Ph.D.
  • 年度 2015
  • 页码 260 p.
  • 总页数 260
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

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