Implementation of Shaft and Tunnel Excavation Monitoring System in the Deep Tunnel Sewerage System Phase 2 Project Lai Lynn Woo, Aung Ko Ko Soe, Kyi Khin, Darryl Tan National Water Agency PUB, DTSS2 Department, Conveyance, Singapore Angus Maxwell, Elpidio Valdez. Jr Maxwell Geosystems, Singapore ABSTRACT: Singapore’s Deep Tunnel Sewerage System Phase 2 (DTSS2) project comprises 50 km of tunnelling work by 19 Tunnel Boring Machines (TBM) and another 50 km of link sewer pipe jacking work to channel used water to a new centralised water reclamation plant to be constructed at Tuas – Tuas Water Reclamation Plant (TWRP). A number of the tunnel shaft locations also include Air Jumpers (AJ), Odour Control Facilities (OCF) and hydraulic structures. Therefore, construction of DTSS2 will produce significant amount of data every day particularly from well instrumented TBMs and pipe jack machines. Since PUB recognizes the volume of data during construction, the Shaft and Tunnel Excavation Monitoring System (STEMS) is introduced in DTSS2 project to integrate all construction monitoring and tunnelling data into a common system environment. The aim is to deliver better quality and timely data with various analytics and reporting capabilities for decision making and risk management. Therefore, engineering geological data, geotechnical instrumentation data, excavation data, TBM and pipe jacking machine data, construction progress and other metadata across the project are taken into the system for processing and integrated into various user definable formats to facilitate quick review and combined analysis. The web-based and integrated nature of this centralised processed data management system also has real-time TBM monitoring capability and automatic SMS alerting feature. Hazards and risks, which are always linked to ongoing activities and planning, can also be identified ahead of time. This paper focuses on the application and implementation of STEMS and also highlights the importance of collaboration for successful implementation. 1 INTRODUCTION The Deep Tunnel Sewerage System (DTSS), an underground highway for used water management, is a core water infrastructure which provides a cost-effective and sustainable solution to support Singapore’s continued growth and meet its long-term needs for used water collection, treatment, reclamation and disposal. DTSS Phase 1 (DTSS1), comprising the North and Spur Tunnels, the associated link sewers, the Changi WRP and outfall, was completed in 2008. DTSS Phase 2 (DTSS2) comprises the South Tunnel which conveys domestic used water, the Industrial Tunnel for non-domestic used water, associated link sewers and the Tuas WRP. The DTSS2 conveyance system has 100km of deep tunnels and link sewers of which 50km is constructed by 19 Tunnel Boring Machine (TBM) and 50km by pipe jacking. Deep shaft and manhole excavations are also required to facilitate launching/receiving the boring machines and to construct associated hydraulic structures. The tunnel construction is split into 5 design & build contracts (Contract T-07 to T-11) and link sewer construction by pipe-jacking is split into 3 schedules (Schedule I, II and III) where each schedule is packaged into 3 to 5 build only contracts. Geographically, the tunnel alignment runs largely under major expressway corridors at between 35 to 55 metres below ground and is bounded by transportation infrastructures, educational institutions, healthcare, commercial, industrial and residential buildings. The geological formation prevailing in the project area is Jurong Formation which is notorious for high groundwater inflow during excavation and tunnelling works. Pockets of soft soil deposits from Kallang Formation are also present locally some distance above the tunnel horizon. It is known that excavation and tunnelling process inevitably causes disturbance to surrounding ground and further leads to ground settlement, even induces severe hazards to structures and infrastructures (Yin et al. 2017, Wang et al. 2019, Yin et al. 2020, Zhang et al. 2021). Therefore, all potential risks must be assessed and a comprehensive monitoring regime established to ascertain an acceptable level of security for existing structures in excavation and tunnelling influence zone.