Category: White Papers

Raising EPB Performance in Metro-Sized Machines

Singapore is employing more than 29 earth pressure balance machines (EPBMs) to excavate a single 21 km metro line, Downtown Line 3. Moscow is adding 50 km of new metro line by 2016, 150 km by 2020. China will expand their metro lines tenfold by 2050 to more than 11,700 km. China’s plans for the next two years require 250 EPBMs. With such extensive global metro expansion plans, increasing EPBM performance would have a monumentally positive economic impact, with tunnels being excavated in less time and at lower cost. EPBMs on several projects have recently set performance records. In this paper, the authors examine these and other projects, searching for clues as to why some EPBMs perform at higher rates than others and attempt to determine which causes are in the control of contractors, which in control of the machine designers and how one might replicate high performance on future projects.

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Achieving Fast EPB Advance in Mixed Ground: A Study of Contributing Factors

Earth Pressure Balance (EPB) tunneling in mixed ground conditions is a challenging prospect, as it often includes excavation in boulder fields, sections of rock, and/or sticky clay, under high water pressure or changing water pressure. Maintaining a rapid advance rate in such conditions is a function of many factors—from adequate cutting tools to cutterhead design, pre-planning and execution of an appropriate ground conditioning regime as well as proper maintenance and operation of the TBM. This paper will analyze recent record-breaking and high-performing projects seeking to identify factors that contribute to fast machine advance. These factors will then be discussed and an effort made to form simple, high level guidelines for optimal TBM excavation in mixed ground conditions.

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Rock Tunneling Machines: Options and Methods for Variable Geology

Modern tunnel boring machines come in a variety of designs that use different excavation methods to address a wide variation of geology seen during tunneling operations. Invariably tunnels of any length run into varying geology, some of which will fall outside the traditional range of any one machine type. On projects where the majority of the drive is rock with a short percentage of a softer formation, selection of a hard rock machine with maximized advance rates, minimized operating cost and wear would be desirable. However, when there are concerns associated with risks of the machine getting stuck, of high water inflow and of subsidence in soft ground, the contractor may be driven towards the choice of a soft ground machine. This paper will review the additional features and ground treatment options that could expand the spectrum of projects benefitting from a hard rock type machine, even when sections of soft ground are present.

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Logistics of Limited Space Urban Tunnelling at Singapore’s Mega Metro

Today’s mega metro projects are using multiple TBMs in difficult ground, short tunnels, and in urban settings: Factors that create unique challenges. At Singapore’s metro construction, 21 km of tunnel for the Downtown Line 3 are underway using 29 TBMs boring between 16 station sites in short bores often less than 1.5 km each. By 2017, 39 km of new construction will cut commute times in half in one of the world’s most densely populated locales.

This paper will detail six earth pressure balance machines on the project, analyzing the challenges of boring in a highly urban setting through rock and soft ground under water pressure. Machine performance at the Singapore Downtown Line will be analyzed with a discussion of the challenges involved.

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The Greatest Challenges in TBM Tunneling: Experiences from the Field

TBM tunneling is an ever-increasing prospect for underground construction, and with each new tunnel bored there are unknown elements. When boring through the earth, even extensive Geotechnical Baseline Reports can miss fault lines, water inflows, squeezing ground, rock bursting, and other types of extreme conditions. This paper will draw on the considerable field service experience within Robbins to analyze successful methods of dealing with the most challenging conditions encountered.

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Continuous Conveyor Design in EPB TBM Applications

While continuous conveyors have become the muck removal system of choice in long, hard rock TBM tunnels, they have gained acceptance in soft ground tunnels only recently. Soft ground, EPB TBM-driven tunnels provide a challenging environment for continuous conveyors due to the variety of materials present. The design of both horizontal and vertical soft ground conveyors will vary depending on the types of excavated material, amount of water present, and other factors. This paper will address the challenges of effective conveyance in different ground materials by analyzing conveyor performance in several recent EPB TBM projects.

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Urban EPB Tunneling in Limited Space: A Case Study of the San Francisco Central Subway Project

The San Francisco Central Subway project is a challenging modern example of urban tunneling in limited space conditions. Two 6.3 m diameter Earth Pressure Balance Machines (EPBs) are excavating parallel 2.5 km long tunnels under low cover and in mixed ground conditions. The small launch site situated between an interstate and an off-ramp, highly curved tunnel alignment, and geology are particular challenges. These elements required customized tunnel and machine design, from TBM shipment and assembly, to launch and excavation.

This paper discusses the project challenges and solutions at the Central Subway project, with a focus on TBM and continuous conveyor logistics. Requirements of the project include explosion-proof electrical components, laser-guided survey, rubber-tired supply vehicles, and machine and back-up solutions for steep inclines and tight curves.

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