ABSTRACT
Groundwater control measures are very important and desirable to implement in urban deep excavation and tunnelling processes to prevent excessive drawdown and subsequent settlement. They form an integral part of the project to protect the various stakeholders’ interests such as deterioration of construction performance and significant impact to existing utility services and building structures. In Singapore’s Deep Tunnel Sewerage System Phase 2 (DTSS2) Project, a major used-water infrastructure project, criteria and guidelines for ground water control scheme are outlined in the contract specifications for implementation at all of its deep tunnel shaft excavation sites. In this requirement framework, there is no restriction to the approach, method and procedure used on groundwater control based on prevailing ground condition and construction schedule. Following the guidelines, detail plans and designs for groundwater control scheme such as permeation grouting, pumping test, monitoring & groundwater recharging, are developed for implementation at each tunnel shaft location. However, there are certain sites in the project where implementation of such a pre-groundwater control scheme is subject to own assessment. This paper briefly explains the concept, principle, and procedure implemented, and also reviews the effectiveness and the benefits of groundwater control in construction risk mitigation.
