Category: White Papers

Long Haul TBM: Use of a Rebuilt Main Beam Machine at the DigIndy Tunnel System in Indianapolis, IN

TBMs can last for decades and be rebuilt project after project with proper maintenance. How successful can rebuilt TBMs be? At the DigIndy Tunnel System in Indianapolis, Indiana, USA, a rebuilt TBM was used to great effect. The 6.2 m diameter Main Beam, originally manufactured in 1980, bored 40+ km of tunnels and set three world records in its size class of 6 to 7 m, including a best month of 1,754 m. In this paper, the authors analyze the TBM rebuild, performance and lessons learned to make recommendations for future projects seeking to use rebuilt TBMs over long distances.

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Evaluating TBM Design and Performance, 30 Years Apart: The Lesotho Highlands Water Tunnel, Phase 1 and Phase 2

Two massive tunnel projects 30 years apart: The Lesotho Highlands Water Project (LHWP) is a multi-phased project that has taken place over decades to provide water to the Gauteng region of South Africa and to generate hydroelectricity for Lesotho. Phase I tunneling began in 1992 and utilized multiple Main Beam TBMs to bore long tunnels in basalt and dolerite ground conditions. Phase II, now under construction, consists of 38 km of transfer tunnel to be excavated by both TBM and drill & blast.

This paper details the design for the TBMs to be used on the Phase II tunnel, while comparing the modern-day machines to the history-making Main Beams used in the 1990s. It draws some conclusions and lessons learned about boring in volcanic rock at depth utilizing Main Beam vs. Double Shield TBMs.

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Use of a Tunnel Boring Machine on Nepal’s First and Second TBM-Driven Tunnels

Nepal’s mountainous terrain has historically been a challenge to tunnel through. That very terrain also holds great promise for hydropower – a resource that the country is now beginning to tap into. Launched in October 2022, a 6.4 m Double Shield TBM is making Nepal’s hydropower plans into a reality as it bores the 13.1 km headrace tunnel for the Sunkoshi Marin Diversion Multipurpose Project (SMDMP). The tunnel is connected to a 28.6 MW surface powerhouse on the Marin River.

The SMDMP is the machine’s second tunnel: on its 12.2km first tunnel (the Bheri Babai Diversion Multipurpose Project/BBDMP), the TBM finished nearly one year early and achieved 1,202 m advance in one month. It was the first instance of TBM use in the country.

In this paper, we examine the successes and lessons learned in Nepal’s mountainous conditions during excavation of both the SMDMP and BBDMP.

 

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Record-Setting Large Diameter Mixed Ground Tunneling in Turkey: The Eşme-Salihli Railway Tunnel

Large diameter tunneling has historically been seen as a challenge. Add into the equation mixed ground conditions, and it becomes a task that may seem insurmountable. How-ever, a recently completed tunnel in Turkey is a flagbearer for changing the mindset towards these challenging tunneling scenarios that are becoming more frequent. A 13.77 m diameter mixed ground Rock/EPB TBM bored the Eşme-Salihli Railway Tunnel at rates of up to 721.8 m in one month, making it the fastest TBM ever recorded over 13 m in diameter. The machine began its bore in altered gneiss, then passed through mélange consisting of gneiss, sandstone, claystone, mudstone, quartz, and silt. By the end of the bore the machine was excavating in mainly mudstone. Core drillings were taken every 200 m prior to boring.

In this paper, we detail the project as well as analyze factors contributing to the fast advance rates. The factors include TBM choice and system design, ground conditions, TBM utilization rates and downtimes, as well as maintenance practices, crew expertise and technical support, all of which have a part to play in the overall advance rates and successful outcome. Recommendations are made as to best practices in order to achieve good advance rates on similar large diameter, mixed ground tunnels.

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Lessons Learned During Excavation of the Incredibly Challenging Yin Han Ji Wei Water Diversion Tunnel

The 2022 breakthrough of an 8 m diameter Main Beam TBM at China’s Yin Han Ji Wei project was a triumph of technology and perseverance – crews at the 17.5 km long tunnel encountered over 14,000 rock bursts, some with energy as high as 4,080 kJ. The rock, consisting of mainly quartzite and granite, was estimated to have a rock hardness of between 107 and 309 MPa UCS, with high abrasivity and a maximum quartz content of 92.6%. The incredibly challenging tunnel also experienced at times severe water inflows, with one particular event exceeding 20,000 m3 of water in one day from a single point. In-tunnel ambient temperatures peaked at 40 degrees Celsius and 90% humidity. Throughout the challenges, the crew and support teams found ways to persevere – whether through unique ground support, or increased monitoring and analysis. In this paper, we will examine the successes and lessons learned in the incredibly challenging ground conditions, determining what worked best to confront each condition as it came up. Recommendations will be made towards what could be used successfully on future projects that en-counter these geological features.

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Record-Setting Tunnel Boring Below Lake Ontario at the Ashbridges Bay Outfall Tunnel

The 3.5 km long Ashbridges Bay Outfall in Toronto, Ontario, Canada was a challenging drive set below Lake Ontario. After a remote machine acceptance due to the global pandemic, an 8 m diameter Single Shield machine launched in March 2021 from an 85 m deep shaft and began its bore in shale with limestone, siltstone and sandstone. During excavation, the TBM and its crew bored a city-wide record of 30 rings in one day, or 47 m of advance. This paper will cover the unique project, from TBM acceptance through to launch, tunneling in difficult conditions, and completion in 2022.

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Enhanced Probe Drilling & Pre-Grouting on Hard Rock TBMs

While probe drills are not strictly necessary for all projects, the incorporation and use of probe drills and pre-grouting adds capability and insurance to boring operations. Water ingress and unstable ground can be resolved before becoming a problem and resulting in costly delays through the use of enhanced, 360-degree probe drilling setups. To do this, proper design of the array of drill ports in the shield, matched to the possible ground conditions, is critical. For ground with exceptional water and instabilities expected, additional probing locations are low-cost additions that can lower risk and increase efficiency. In this paper we will look at recent and ongoing projects including the Lower Meramec Tunnel and Jefferson Barracks Phase 2. We will detail the design of those probe drill arrangements, and our overall recommendations for probing/grouting systems that best suit challenging ground conditions and keep projects running smoothly.

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A Clean Solution for Renewable Energy: Small Diameter Hydro Tunnels

Small hydroelectric power projects, with installed capacity up to 10 MW, are a relatively untapped but potentially game-changing source of renewable energy worldwide. In Norway, hydro projects are pioneering the use of small diameter TBMs in hard rock. Compared with drill and blast, TBMs offer increased production rates and reduction in cross section, as well as lowered rock support requirements and reduced project schedules.

The uniquely designed machines are engineered to take on steep gradients, up to a 45-degree angle in some cases. Both shielded and open-type TBM designs have been developed that utilize safety grippers and customized mucking systems to operate at steep grades. This paper will discuss the specialized TBMs and their performance at several projects in Norway, as well as the potential to use this technology throughout Europe and internationally.

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Non-Circular Tunnel Boring for Underground Mine Development

TBMs have been used in mining in decades past, but their use has been limited and sporadic. This has changed in recent years, with TBMs being used at Stillwater Mine, Grosvenor Coal Mine Slopes, and Sirius Minerals potash mine. These machines are all full face, circular TBMs. With their circular bores, these machines have thus far been unable to tackle a larger issue for mines—the need for a flat floor. While the mining industry excavates many more kilometers of tunnel each year than the civil construction industry, typically a flat floor is needed for mining vehicles to traverse.

A novel type of non-circular boring machine is now answering that need with its ability to cut a rectangular profile in hard rock. This cross section allows for use of typical mine trucks and other rubber-tired mine vehicles. It provides more useable space, compared to a circular profile, and minimizes the amount of excavated rock that must be hoisted out of the mine. This machine uses typical disc cutters to cut the rock and has a support structure similar to an open type TBM; however, the cutting geometry is entirely different. The machine is currently cutting an access tunnel at a silver mine.

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Unprecedented In-Tunnel Diameter Conversion of the Largest Hard Rock TBM in the U.S.

The largest hard rock TBM ever to bore in the USA, an 11.6 m diameter Robbins Main Beam TBM, recently underwent a planned in-tunnel diameter change to a more compact 9.9 meters. The first-of-its-kind conversion process for the Main Beam TBM was undertaken 2.8 km into the bore and was not done inside a shaft or pre-excavated portal. This paper will detail the unique dual-diameter machine designed for the Mill Creek Drainage Relief Tunnel in Dallas, Texas, USA, machine performance, and successful size conversion process that took place in early 2021—a process that utilized the four C’s of construction to enormous benefit: Communication, Cooperation, Collaboration and Coordination.

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