Category: White Papers

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.

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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.

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Excavating Turkey’s Hardest Rock at the Bahce-Nurdag Railway Tunnel

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.

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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.

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Difficult Ground Solutions (DGS): New TBM Solutions carve a Path to Success

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.

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The Return of TBMs to Norway at Røssåga HEPP—TBM Operation Through Extremely Hard Rock, Unstable Rock Mass, and Other Challenges

The TBM that broke though at Røssåga HEPP in December 2015 was the first to breakthrough in Norway in more than 20 years. During the excavation the TBM encountered extremely hard rock (over 280 MPa), which posed an extreme challenge for both the TBM and the cutters. During the excavation a highly efficient main bearing replacement was also performed in the tunnel. This paper discusses the project as a whole, including TBM design, Onsite First Time Assembly (OFTA) of the machine, challenges faced, and project outcomes.

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Large-Diameter 20-Inch Disc Cutters: A Comparison of Tool Life and Performance on Hard Rock TBMs

Optimization of disc cutter life and penetration rate in hard rock can be one of the biggest predictors of project success. With hard rock TBMs being used today in ever more difficult conditions and longer tunnels, the question of which type of disc cutter to be used becomes critical. At one such project in Northeastern China, varying disc cutter tool steels and sizes were put to the test on a total of nine different 8.5m diameter hard rock, Main Beam TBMs from various manufacturers. The TBMs excavated sections of a vast water tunnel in similar granitic geology.

This paper will look at the development of 20-inch disc cutters and the case for large diameter cutters, using the most recent example in China as a focus area of study. Varying advance rates, cutter life, tool steels, and challenges excavating the rock will be discussed. The paper will conclude with recommendations for optimal cutter life in TBMs destined to bore long tunnels in hard rock.

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Use of “Command Chair” Simulator Technology to Optimize Modern TBM Performance

TBM operator cabs and controls are often a long way down the list of priorities when it comes to the overall design of a Tunnel Boring Machine. However, their proper design and inclusion of the latest technology can mean the difference between a successful project and an unsuccessful one.

On soft ground machines the industry often puts operators in control of machines with little or no practical experience of that particular machine or the control systems. This practice can, in some cases, lead to major incidents such as ground heave or sinkholes in densely populated urban zones causing major disruption, downtime and untold damages and cost.

This paper will discuss the advances and developments in TBM operator controls and the use of “command chair” technology as both a training tool in the form of a boring machine simulator and as a way of controlling modern-day TBMs.

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Rondout West Branch Bypass Tunnel—TBM Boring in Hard Rock Against High Water Pressure and High Water Inflows Beneath the Hudson River in New York

This paper focuses on a single shield hard rock tunnel boring machine that is set to bore in hard rock, high water inflows and high water pressure in New York State. To overcome the difficult conditions the TBM is designed to handle 2500 gpm water inflows and seal against 30 bar of pressure. The TBM will bore a tunnel to replace a damaged portion of the Delaware Aqueduct that supplies half the raw water to New York City. The 2.5 mile bypass tunnel passes beneath the Hudson River with geology consisting of shale and limestone.

Due to the high water pressure and inflows, the TBM was designed with new sealing systems for the main bearing and to close the TBM off if high water inflows are encountered. The TBM is to be equipped with two dewatering systems and multiple drilling and grouting systems for pre excavation grouting and segmental lining backfill. Systematic drilling and grouting procedures specific to the project were developed and incorporated into the TBM and backup design to ensure that the TBM can handle the extremely difficult ground conditions of the project.

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A Smart Disc Cutter Monitoring System Using Cutter Instrumentation Technology

In mechanized tunneling, continuous information from the excavation face is essential. The ultimate goals of cutter instrumentation are to monitor real-time individual cutter operation, acquire more realistic cutterhead thrust force values, and gain a better knowledge of the geology in front of the cutterhead. Analysis of this information can provide in-depth knowledge of machine excavation. Information about cutter operation has direct and indirect advantages: It helps better predict and monitor cutter usage rates, and it can reduce the cost of unplanned cutter or ring replacement, which can result in a better planning of inventory, manpower, and cutter rebuild requirements.

Current disc cutter instrumentation technology is designed to be a conveniently mounted instrumentation package that monitors individual cutter rpm, wear, temperature, and vibration. A data logger service receives the cutter information wirelessly using low-power radio technology and displays cutter conditions in real time. With cutter instrumentation, the operator continuously monitors cutter conditions, which results in higher efficiency, lower incidence of down time, and prevents unexpected ring wear-related damage from causing further damage to bearings and hubs. Cutter instrumentation technology has been tested on Robbins’ rock machines and results from previous and recent projects are presented. Design improvements for longer lifetime and increased reliability are discussed.

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