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.

For this important reason, TBMs used in the project are heavily instrumented for efficient operation and better control to minimize the risk of over-excavation which can cause ground collapse and depression on the surface. Likewise, extensive arrays of geotechnical instrumentation are also required to be installed along the tunnelling corridor for monitoring. The substantial quantity of data generated from TBMs and geotechnical instruments require an efficient method for processing and delivering useful engineering data to interpret and assess the level of risks at all times. The most promising and prevalent method to do so is to create a common data environment using web and cloud computing technologies. With reliable and sufficient communication of monitoring data and in-situ construction information on a co-ordinated data platform, it is easy to devise appropriate action plans to avoid major hazards. Therefore, DTSS2, being a major tunnelling project in a densely populated urban area, requires a centralised integrated data management system implemented to deliver better quality and timely data with various analytics and reporting capabilities for decision making and risk management.

2. Background

In urban tunnelling and excavation works, geotechnical instrumentation data and TBM operation parameters are of paramount importance, and close monitoring is vitally important for safe and successful operation. Therefore, centralised database management systems are increasingly utilised in excavation and tunnelling project as they offer the ability to integrate various types of field information and relay this to decision makers in real time. Monitoring data in urban tunnelling projects are generally of two types: real-time data and non-real-time data. Real-time data are data from TBMs, Slurry Treatment Plants (STP), Slurry Transport Systems (STS), Automatic Tunnel Monitoring Systems (ATMS), Real-time Vibration Monitoring Systems, Expressway Monitoring Systems and live CCTV streams. Non-real-time data are manual instrumentation readings, soil investigation bore logs, reports, drawings, records, photographs, etc. Traditionally, these types of data are processed and managed separately on different platforms. Therefore, it is time consuming or operator intensive when combining and integrating this data for analysis.

Nielsen & Koseoglu (2007) pointed out that construction information monitored by manual work was expensive and limited. Moreover, it exhibits the lag effect and thereby cannot assist with the prompt decision making and instruction that is required for tunnelling and excavating work. In fact, there are several monitoring systems used in the industry. However, most of them are only designed to work with specific types of monitoring data and not capable of integrating diverse construction data from various sources. For example, most of the conventional TBM monitoring systems do not incorporate instrumentation and ground condition data or their availability is limited to PDF or non-interactive provision only. When cross-correlation is required, it has to be done manually using spreadsheet or graphic editor software. Depending on the types and volume of data, the process would take from a few hours to even up to a few days in some cases. But with an efficient data management system, it can be done conveniently with a few mouse clicks. Therefore, centralised integrated data management systems are becoming popular in urban tunnelling projects as they also carry many other benefits such as improvement in transparency, quality and timeliness in construction data delivery and accessibility.

Recognizing the recent development of data management systems and its applicability, Singapore’s National Water Agency (PUB) decided to utilize a Shaft and Tunnel Excavation Monitoring System (STEMS) as a centralised data platform in DTSS2 project to collate diverse monitoring and construction data, convert it to user-friendly formats and deliver it with appropriate analysis tools. As excavation and tunnelling performance relates to multiple factors, engineering geological data, geotechnical instrumentation data, excavation data, TBM operation parameters, construction progress and other associated data are taken into the system to facilitate the combined analysis and interpretation. With this system in place, it is able to retrieve the information which would not be readily available in conventional systems or hidden in the diverse field data. Therefore, loss of essential construction information can also be avoided.

3. Project Management

PUB awarded the contract for the provision for the Shaft and Tunnel Excavation Monitoring System (STEMS) to Maxwell-Geomotion Joint Venture (MGJV) in September 2017.The duration of the contract is 89 months in which the first 7 months is given for system development. Before the deployment, acceptance test and system performance checks were carried out with dummy data. The developed system, STEMS, is designed to support 5 tunnel contracts, 12 link sewer contracts, 9 instrumentation contracts and an influent pumping station construction contract with unlimited number of users. Upon the completion of project, all data and software shall be handed over to PUB. The system scope and delivery are managed by PUB and its consultant, Binnie and AECOM Joint Venture.

4. Stems Overview

STEMS is developed as a web-based integrated data management system using GIS concept on MissionOS platform which is designed to work with diverse construction data. This system is neither a desktop application nor a ready-made software. It runs on any web browser and is configured according to DTSS2 contract specifications and project requirements. STEMS is different from conventional instrumentation monitoring systems or TBM monitoring systems as it also functions as a coordinated data management platform which bring together various construction data and transform them into useful engineering information. As such diverse data in their native formats can be combined or integrated because STEMS collect and collate them directly from their sources and process them in a way that everything can be combined and viewed in a single common platform (Figure 1).