Client-Contractor Collaboration for Integrated TBM Process and Geotechnical process Control – Power Grid Cable Tunnels Singapore

For many years partnering has been a well-established principle for promoting a “best for project” culture within a construction contract. This endeavors to remove the adversarial nature of classical “engineer’s design” contracts by openly discussing issues which may impact on project performance and look to engineer ways to mitigate them within the terms of the contract. These discussions rely on information and often the data available to client, engineer and contractor is incomplete, different or ‘selectively’ chosen to support a particular point of view. On many contracts clients have implemented project wide systems either independent of the main contractor or as part of the contractor’s specification and these have seldom provided the common information base desired in order to facilitate the partnering approach. The Powergrid Cables tunnels in Singapore represent the first time that all contractual parties have contributed to the implementation of project wide data management systems. The paper will describe the systems; their technical capabilities within TBM process and geotechnical control, their implementation and the contractual framework origins within which they have been delivered.

Keywords

Data system, Partnering risk

 Introduction

The North-South, East-West and Jurong Cable tunnels currently under construction by SP Powergrid in Singapore are the second set of deep tunnels constructed by Singapore Power. The first phase of tunnels faced a number of challenges, many relating to tunnel depths in excess of 40m below the water table. The most acute of these challenges involved flowing sand conditions which led to a stoppage of several months on one TBM drive. In planning phase 2 of the scheme the designers were also obliged to set the tunnels deep to avoid other infrastructure such as metro, sewage, drainage culverts and road tunnels. At this depth, the tunnels would be passing through old alluvium, decomposed granite soils, metasediments of the Jurong Formation and Bukit Timah Granite with a high proportion in mixed face. Occasional exotic conditions such as lavas, eutaxitic and ignimbrites in addition to volcanic breccias would be expected. Faulted ground was expected and in some cases is suspected to be linked to hydrothermal water. The water table is high and the near surface soils including peat, alluvial clays and residual soils are sensitive to water drawdown.

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