Journal of Zhejiang University-SCIENCE A

, Volume 19, Issue 4, pp 255–265 | Cite as

Discontinuum analyses of openings constructed with side drift and limited rock cover

Article

Abstract

The design of rock support for a typical horseshoe shaped tunnel with considerations of it being excavated into a twin arch tunnel was studied using the distinct element method (DEM). Two different competent rock covers, i.e. 4 m and 7.5 m above the tunnel crown, were analysed. The results are relevant to the granitic geological unit in Singapore which has a weathering profile with rockhead found at some locations to be only 20–35 m below ground level and undulating, leaving limited rock cover for some sections along tunnels of similar depth. The verification of the adequacy of competent rock cover is important to ensure that the choice of ground support is suitable, particularly when the tunnel is excavated using the drill-and-blast method. In the opening geometry analysed in this study, a side drift is excavated adjacent to the first tunnel to create a twin arch opening. This creates a pillar between the openings during the intermediate construction stage. The influence of excavating the side drift on the support of the first opening was studied. We found that the bolt forces in the pillar approximately doubled during the excavation of the side drift, which may have been due to the rock joint inclinations and adopted strength parameters. This paper shows how DEM analyses may be used to complement conventional empirical rock mass classifications to design rock supports. Limitations of the pressure relaxation approach to model 3D effects in 2D are acknowledged.

Keywords

Rock cover Twin tunnel Side drift Pillar Distinct element method (DEM) 

关于具有测边导坑和有限岩石覆盖层的隧道开口 的离散分析

概要

目的

针对新加坡的花岗岩地质结构,研究将典型马蹄 形隧道挖掘成双拱隧道时岩石支撑的设计问题。 利用离散元法分析侧边导坑对隧道主体开口的 影响。

创新点

1. 基于平面应变假设, 提出一个针对性的离散元 模型以分析侧边导坑的设置对主体隧道支撑的 影响;2. 此模型适用于解决底下长跨度开口的支 撑设计问题,如大众捷运系统隧道和紧贴式双孔 隧道的建造,补充了传统经验主义的设计方法。

方法

1. 采用离散元法对马蹄形隧道开口支撑问题进行 非连续分析;2. 采用二维平面应变模型简化问 题。

结论

1. 离散元法可用于分析有限岩石覆盖层的失效机 制,单隧道支撑要求以及增加侧边导坑后的支撑 要求;2. 模型计算结果显示,侧边导坑的挖掘使 得支柱总的螺栓连接作用力增加了一倍。

关键词

岩石覆盖层 双隧道 侧边导坑 支柱 离散 元法 

CLC number

TU45 

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Notes

Acknowledgements

The work was undertaken at One Smart Engineering Pte Ltd., Singapore in 2016. The authors would like to thank the organisation for the encouragement. The analyses presented here do not indicate a preference for the numerical methods by the institutions to which the authors are affiliated.

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Copyright information

© Zhejiang University and Springer-Verlag GmbH Germany, part of Springer Nature 2018

Authors and Affiliations

  1. 1.One Smart Engineering Pte Ltd.SingaporeSingapore

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