David Ng is Executive Director of ONE SMART ENGINEERING with offices in Singapore and Malaysia. He is a Specialist Geotechnical PE registered with Singapore PEB. He graduated in 1999 with a Master Degree in Geotechnical Engineering from NUS where he received the Innovation Award and NSTB Gold Award for his outstanding academic results and research work. In 2000, he was awarded the First Prize of the prestigious Hulme’s Competition by the Tunnelling & Underground Construction Society of Singapore for his technical paper in tunnelling. In 2013, he has received the Young Consulting Engineer Award 2013 by the Association of Consulting Engineers of Singapore (ACES). He has published 39 technical papers in the field of geotechnical engineering. He has been involved in the design, supervision and project management of major infrastructure projects with deep excavation, mined tunnels and bored tunnels in Deep Tunnel Sewerage System, Kallang Paya Lebar Expressway, North East Line, Circle Line & Downtown Line during his 16 years of working experience.
Presentation Title
More Sustainable Underground Infrastructure Projects by Observations by Observation Approach - A Case Study of Singapore MRT Downtown Line Contract C922 Project
Abstract
Contract C922 Overrun Tunnel is part of Package C9181C Downtown Line Stage 3. The Overrun Tunnel (ORT) basically an underground facility building functions as both Railway Facility (Operation Control Centre) and Electrical Substation (ESS) which is to be built next the Expo Station. . The overrun tunnel is located in the area of intersection of Changi South Avenue 2 and Avenue 3 as shown in Figure 1. ORT is located in old alluvium (OA). The proposed underground overrun tunnel is a box structure with dimensions of approximately 23m wide, 25m deep and approximately 440m long. The proposed diaphragm wall function as the earth retaining system (ERSS), it designed for both temporary loading conditions during excavation and permanent load conditions in accordance with LTA Civil Design Criteria. Bottom-up construction sequence is adopted where lateral supports using four (S3 to S6) or six (S1 to S6) layers of steel strutting were installed as excavation progresses downward. The challenges for ERSS at this project include its close proximity to the existing buildings that requires stringent control on ground deformation and controlled working hours with tight construction schedule. The most challenging part is the omission of the last layer of strut S6 for the whole ORT by using observational approach. The approach to the back analyses and forward analyses in this observational approach is presented in this paper. This paper will also discuss the design and construction considerations by focusing on the challenge of strut omission by observation approach. The instrumentation monitoring results will also be presented as evaluation of the performance of the ERSS. The site observation and instrumentation result is in line with the forward analysis prediction for the omission of strut. This proposal has helped to expedite the project with a more economical design. With the implementation of observational approach, we will be able to achieve a more sustainable development of underground infrastructure projects.