Geotechnical Process Control | Risk analysis in construction industry

 

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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Northeast Boundary Tunnel | DC Water clean project

The Northeast Boundary Tunnel (NEBT) is a reinforced concrete sewer tunnel (7m diameter, 15-48m deep), that will increase the capacity of the existing sewer system in Washington DC’s North East District. Maxwell GeoSystems is providing its industry leading MisssionOS cloud-data platform, to meet the client’s needs for real-time feedback of ground deformation in conjunction with shaft construction & key TBM operation parameters. Due to the sensitivity of surrounding infrastructure, the client relies on MissionOS ’s real-time alarm notification system to alert key parties of potential unwanted settlements. Addtional key features implemented on this job include proximity functions to relate ground deformation to TBM operations, prediction models to estimate final settlement, and TBM parameter alarms. The NEBT is the largest component of the Clean Rivers Project in Washington DC (USA) and will be built using the TBM “Chris” (92m in length). The tunnel project faces a number of challenges including heavy clay and water bearing clayey sands at water pressures up to 3bar, a challenging alignment with 15 curves, and a complex work environment for shaft construction with small shaft sites combined with urban residential neighbourhoods and a high traffic corridor. Parties afiliated with the Project: Designer: Brierley Associates; TBM Supplier: Herrenknecht; Slurry Walls, Jet Grout, Secant Piles, Solider Piles: Treviicos; Segmental Tunnel Liner Supplier: ConSeg JV; Muck Hauling: Bulldog; Construction; Instrumentation: Entech; Traffic Engineering & Instrumentation Installation: EBA; Construction Manager: EPC Consultants; DC Clean Rivers Program Manager: McMillan Jacobs and Greeley & Hansen.

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