Diminishing surficial mineral deposits, increasing environmental regulation and advanced geological exploration techniques are ushering in a new era of mining. Unconventional technology must be adopted to ensure that safe, efficient and responsible access to minerals is possible as prospecting continues to push the mining industry deeper. This paper discusses why competitive mining operations will become increasingly dependent on Tunnel Boring machines (TBMs) for mine development and expansion, and explores the implications of TBMs in a drill and blast dominated industry.
Lessons learned from construction of the 62km Emisor Oriente Tunnel in Mexico's challenging and varied ground
In April 2009, tunnel boring started on the Tunnel Emisor Oriente (TEO) sewer project after decades of deliberation. The infrastructure will replace an open, untreated canal that conveys wastewater from Mexico City. The new tunnel will end at the capital’s first wastewater treatment plant and reduce the risk of catastrophic flooding in downtown Mexico City. It was this risk that led President Felipe Calderon to label the project a “National Emergency”. The TEO project was designed as a 62 km pipeline of 8.9 m diameter with a primary precast concrete segmental lining and a secondary in-situ concrete lining. 24 shafts up to 150 m deep support six TBM operations totaling about 10 km each. After five years of work, 34% of the bore is complete, and the owner of the project, CONAGUA, is rethinking their strategy based on incredibly difficult ground. This paper will discuss the new strategy from both the contractor and manufacturer perspective, including successful TBM modifications.
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.
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.
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.
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.
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.
- Rebuilding TBMs: Are Used TBMs as Good as New?
- Breaking Through Tough Ground in the Himalayas: Nepal's First TBM
- Tunneling in Mixed Face Conditions: An Enduring Challenge for EPB TBM Excavation
- 7.93 m Open TBM Shotcrete System Improvement and Innovation - Jilin Project, China
- Overcoming Extreme Tunneling Conditions in Vietnam's Longest Tunnel