Tunnel Business Magazine

OCT 2018

TBM: Tunnel Business Magazine is the market leader for North America. TBM is written for leading professionals in all aspects of tunneling and covers project stories, design elements, contracting strategies, legal issues, new technology and more.

Issue link: http://digital.tunnelingonline.com/i/1042145

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Page 29 of 47

TUNNELINGONLINE.COM F E AT U R E S T O R Y 3 0 TBM: TUNNEL BUSINESS MAGAZINE // OCTOBER 2018 We all know that tunnels are essen- tial to modern infrastructure, but what is the best way to drill a tunnel? The three defining methods are the Tunnel Boring d, the Cut-and-Cover ap- pr unneling o referred to as the Sequential Excava d onventional tunneling. Each method holds a set of strengths and weaknesses that make it the better ap- proach for certain applications. In this article, we will discuss one meth- o un- ompare its merits to the others. What is NATM? oth a construction method and a design philosophy. The philosophy looks to use the strength of the surround- ing soil to the greatest extent possible to strengthen the tunnel structure. In other words, ground conditions drive the tun- neling opera ophy also promotes constant monitoring. onstruction method is about flexibility—drilling and designing depending on the results of the ongoing monitoring. The operation occurs se- quentially to take most advantage of the ground conditions. Additionally installs ground support on the go and on an as-needed basis, adding reinforce- ment to the shotcrete where necessary. The final, permanent support is usually (but not always) a cast-in-place concrete lining placed over a waterproofing membrane. est suited for short-range (> 2 km) tunnels in regions with variable soil conditions. Its philosophy and construc- tion method yield a more cost-effective, flexible tunneling operation when com- pared with the other methods. Comparing NATM with Cut-and-Cover The Cut-and-Cover approach func- tions exactly as the name suggests. First, a large ditch is dug into the ground with room for the tunnel. After placing the tunnel, the ditch is covered with soil. This method is effective for building sta- tions and other large segments of a tun- nel with greater space requirements. While Cut-and-Cover is very flexi- ble, it significantly disrupts the ground surface making it ill-suited in dense urban environments or ecologically sensitive areas. Comparing NATM with TBM The Tunnel Boring method has recently earned a lot of press with Elon usk and The Boring Company, who lo onventions (de- creasing tunnel diameters) and pump R&D into improved power, automation, and ef- ficiency mining operation around a machine that drills the entire diameter of the tunnel concurrently. This approach can be been very costly (designing for the worst-load case) and time-consuming. However, once s eration can run indefinitely as the budget permits. Continuous Monitoring and Design with NATM and AGRU is not perfect, needing much co- ordination, cooperation, and communica- tion to compete with the other construction methods. And even at peak performance, erforms at a slower rate than the other methods as the team adapts to changing conditions. F om- pete successfully, the operation must reduce interruptions in excavation and support work by closely working with all elements of the operation to bring in the right supplies for the changing conditions. Understanding the New Austrian Tunnel Method

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