Abstract

The use of Tunnel Boring Machines (TBM) for tunnel excavation is widespread around the world for its capabilities and great advantages against the traditional tunnel excavation method, but sometimes this technology can be difficult to manage, requiring huge spaces for the assembly on the job site and involving complex installations at the tail of the machine.

Aiming at creating a versatile and compact tunnel borer, TunnelPro and Master Drilling designed the MTB (Mobile Tunnel Borer) that is built on crawlers, easy and fast to assembly with no need of special equipment. This prototype MTB is currently excavating a Platinum mine in South Africa, being tested in very hard rocks.

The study here presented, carried out by GEEG srl, startup of Sapienza University of Rome, compares the actual values of thrust, torque, penetration and cutter wear recorded during the trial excavation monitoring with those estimated with models commonly used in TBM performance prediction. The aims of this study, still ongoing, are a better comprehension of the MTB operation in terms of efficiency, work of the excavation tools, load distribution, and the evaluation of the adequacy of the most known methods when applied to this prototype machine.

Introduction

The Tunnel Borer Machine is nowadays the preferred method for the excavation of underground works as subways, railways or hydraulic tunnels in urban as well as non-urban areas, thanks to its many advantages in terms of production, surface displacements control and safety, even if the drill and blast tunneling method can still be more effective depending on the rock conditions, tunnel cross section and length. The drill and blast can be in fact more feasible when the excavation affects a complex geology, when the tunnel has a variable cross section, a high slope or when its length may not justify the initial cost of a TBM, which happens for a length less than about 3 km, as discussed by Zare, Bruland and Rostami [1], Girmscheid and Schexnayder [2].

Due to the above reasons, a field of application so far dominated by the drill and blast tunneling method is mining, despite all the disadvantages that the use of explosives entails for the health and safety department, especially when the ore is deep and the temperatures inside the tunnel are consequently very high. To implement a solution for mining with mechanized tunneling, TunnelPro s.r.l and Masterdrilling Group Ltd designed a Mobile Tunnel Borer (MTB), built on tracked wagons, which assembly takes a few days and does not require a special equipment; an open machine to be applied in rocks that doesn’t need segmental lining but only spot bolting. The prototype MTB was tested in a Platinum mine in South Africa to prove if it could achieve an equal or better advance rate than the mine daily rate of about 1.5-3 m, simultaneously improving safety and logistic.

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