Category: White Papers
Risk management in the world of TBM tunneling is, in itself, a risky business. The underground often presents obstacles and complex projects spanning miles of tunnel multiply those risks. However, there are ways to manage and reduce risk in our industry; i.e., by ensuring that thorough geotechnical studies are done and that contingency plans are in place. The TBM itself can be designed with risk reduction in mind, using tools that expand visualization of the ground around the machine and arm the contractor with ways to get through challenging ground conditions with minimal delays. This paper explores risk in TBM tunneling from the viewpoints of the consultant, the contractor, and the equipment manufacturer. It also seeks to make recommendations as to how risk can be better managed in today’s tunneling industry.
Atlanta, Georgia’s water supply program is a priority project involving a 5.0-mile long tunnel connecting up with the Chattahoochee River, which will establish an emergency water supply for the city. A 12.5 ft diameter Main Beam TBM is boring the area’s deepest tunnel through hard, abrasive Gneiss rock at rates of up to 100 ft per day. This paper examines the project specifics and design, as well as the performance of the TBM. It also draws conclusions as to the optimal TBM design for excavation in the area’s exceedingly hard geology based on this project and past projects in the area.
The abrasive nature of glacial geology generally results in Tunnel Boring Machine (TBM) cutting tool inspection and replacement needs that may require hyperbaric interventions and are a cost and risk factor. Correlation analysis of geotechnical conditions, TBM operational parameters, and tool wear measurements is a proven way to gain insight into the wear system behavior. This paper presents findings from various TBM drives in the Seattle and Vancouver, B.C. metropolitan areas on the performance of disc cutters and ripper-type tools in glacial and inter-glacial deposits. The authors provide recommendations for cutterhead configurations, tool management strategies, and the use of monitoring technology.
Logistics and Performance of a Large-Diameter Crossover TBM for the Akron Ohio Canal Interceptor Tunnel
The Ohio Canal Interceptor Tunnel (OCIT) below the city of Akron is utilizing the first large diameter Dual Mode, “Crossover” type TBM in the United States. The 30.4 ft diameter machine is excavating in variable conditions including soft ground and shale rock. Due to the unique conditions, the TBM has been designed with features including a flexible cutterhead design and abrasion-resistant plating on the cutterhead and screw conveyor. As part of a predictive maintenance plan, measurements for the screw conveyor’s exposed features will be taken along the drive to report on the wear rate of these components in shale. This paper concentrates on the logistics and process of the TBM launch, and component wear and performance at the jobsite in variable ground conditions.
At the Gerede Water Transmission Tunnel in Central Turkey, a 31.6 km long water supply line has been designated a national priority due to severe and chronic droughts in the capital city Ankara. Drawing water from the Gerede River (and conveying to Çamlıdere Dam), it will be the longest water tunnel in Turkey once complete.
But completing the tunnel has been an obstacle in itself. The project has been called the most challenging tunnel currently under construction in Turkey, and with good reason. Out of three standard Double Shield TBMs originally supplied to bore the tunnel, two became irretrievably stuck following massive inflows of mud and debris. In 2016, a hybrid type “Crossover” machine was launched to excavate the final 9 km of tunnel, but to do so it would need to cross dozens of fault zones and withstand intense water pressures up to 20 bars.
To accomplish this, the machine was designed with a number of unique features including the ability to be sealed up to 20 bar pressure. In the event of a large water inflow, the stopped TBM would hold back the water/muck and allow time for pre-consolidation grouting. The machine is also equipped with a bottom screw conveyor and a unique cutterhead design that facilitates effective muck transportation in both hard rock and mixed ground, among other features. This paper discusses the performance of the machine in exceedingly difficult conditions, and outlines the challenges yet to be overcome and how they may be surmounted. The paper also covers the unique aspects of this urgent Turkish projects and the unique logistical requirements of assembling and launching a machine deep within an existing tunnel.
Excavating Mexico City's Mega-Tunnel in Mixed Ground at 150 Meters Deep: Emisor Oriente Wastewater Tunnel Lot 5
Mexico City, with its 19 million inhabitants, is one of the world’s largest cities, but much of its infrastructure is struggling to keep up. Between 1970 and 200 the population doubled and today it produces 40m³/sec of wastewater; however, capacity is only 10 m³. In addition, much of the city’s wastewater is untreated and flows through a network of open sewers and underground lines.
The National Water Commission, CONAGUA, has developed a critically designated plan to assuage health concerns and the potential for catastrophic flooding if a wastewater line should fail. The mainstay of their scheme is the country’s largest infrastructure project, Túnel Emisor Oriente (TEO). The 62 km long tunnel will be connected to the first wastewater treatment plant in Mexico City, and will alleviate flooding. A total of six TBMs are excavating the tunnel in some of the most complex geology on earth.
This presentation will look at the challenges of the TEO Lot 5, examining machine assembly at the bottom of the deep shaft, and modifications and performance in the exceedingly difficult conditions that challenge the limits of the EPB tunneling.
Recent Cutter Technology Advances to Efficiently Bore Through Extremely Challenging Conditions in Hard Rock
For TBMs in hard rock, two of the most important parameters to consider are the cutter performance and the penetration rate. These two considerations are highly dependent on each other, as the cutters are typically the critical components that limit the thrust of the machine—a critical variable that dictates the net penetration rate. In such conditions optimal cutter performance is extremely important, not only to optimize the net penetration rate, but also to minimize the time needed to change cutters and maximize the time available for boring. Over the last five years, massive investments have been made in cutter development to make cutters that can withstand even the most challenging conditions. This paper presents the developments and challenges that have driven the last years’ advances in cutter technology, as well as the results of those developments on recent projects.
Southeastern Turkey’s Gaziantep province is characterized by complex fractured rock within the Eastern Anatolian Fault, and it is now the location of an important railway tunnel project. With a population of nearly 1.7 million, the province is overhauling its public transportation with a rail line between the towns of Bahçe and Nurdağı. The Bahce-Nurdag Railway Tunnel consists of two parallel 9.75 km tunnels being excavated by both NATM (850 m) and TBM (8.9 km).
Contractor Intekar Yapi Turizm Elektrik Insaat San. ve Tic. Ltd. A Robbins Single Shield TBM, 8 m in diameter, was chosen to excavate two sections of tunnel. Mixed ground conditions prevail on the project, and range from abrasive, interbedded sandstone and mudstone with quartzite veins to highly weathered shale and dolomitic limestone. The TBM has thus far encountered some of the hardest rock ever tunneled in Turkey, measuring between 136 and 327 MPa UCS.
This paper will analyze TBM performance, as well as the performance and wear of disc cutters in the difficult ground conditions. It will discuss TBM design and project logistics including onsite TBM assembly in a remote area of Turkey. Finally, it will give recommendations as to proper TBM design and cutter usage in hard, abrasive rock based on the project results.
EPB Excavation of Less Than Five Meters Below the Historic Structure of Chandpole Gate on the Jaipur Metro Project
The tunnels excavated by Continental Engineering Corporation (CEC) for the underground section of the Jaipur Metro project faced the usual challenges posed by metro projects worldwide, including small site footprints, and the associated problems regarding segment and muck storage space, etc. These challenges were, however, relatively straightforward when compared to the challenges faced by the tunneling operations. The Earth Pressure Balance (EPB) TBMs were required to bore under extremely low overburden, alongside and beneath several culturally sensitive historic structures. The age of these structures and their construction methods/materials were of great concern when considering the possible consequences of tunneling-induced ground settlement and vibrations. This paper will describe the measures taken regarding TBM operations and surface monitoring to ensure that these historic structures suffered no adverse effects due to tunneling.
In many TBM-driven tunnels, the occurrence of squeezing ground, high inrushes of water, blocky rock, and other challenges is a real possibility. Difficult Ground Solutions (DGS) reduces risk to contractors and owners in these conditions while providing accurate ground investigation. The story of how these methods came into practice involves hardship that tested the mettle of a shielded hard rock TBM on a recent project. What came out of those challenges is a new way to deal with both predicted and unforeseen ground conditions in rock and mixed ground. DGS features such as dual-range cutterhead drives, high pressure grout injection systems for face stabilization, and water inrush control are customizable and should be considered to be built into shielded TBMs. This paper will cover solutions informed by field experiences, the tools it takes to be successful in difficult ground, and how they are applied.
- The Risks Associated with TBM Procurement and the Next Steps Towards Industry Change
- Boring Hard, Abrasive Gneiss with a Main Beam TBM at the Atlanta Water Supply Program
- TBM Tool Wear Analysis for Cutterhead Configuration and Resource Planning in Glacial Geology
- Logistics and Performance of a Large-Diameter Crossover TBM for the Akron Ohio Canal Interceptor Tunnel
- Excavating Turkey’s Most Challenging Project: The Gerede Water Transmission Tunnel