SPECIALIST EQUIPMENT
some machines still operational 30 years on. Currently machines are also manufactured in China and Australia. Many manufacturers have the bulk of the heavy fabrication undertaken in countries with competitively priced labour rates and with the key complex units manufactured at their country of origin. Typically the TBMs are fully assembled in the factory for an inspection by the client, while some manufacturers are providing the options for the fi rst-time assembly on site, with the advantage of reducing the procurement programme. T e development of TBMs also saw the use of bentonite slurry as a face support and muck spoil transport media, laser guidance systems coupled with segment ring selection programmes, electronic cutter wear systems, data management systems, communication and processing of the sensor data from all equipment/motors. As monitoring and sensor technology developed, belt weighing, CCTV and remote access via internet are now standard features. How fast is fast? Advance rates in hard rock TBMs can be up to 30m/day, 430m/week and excess of 1,000m/month have been achieved. One record I am aware of was in Australia of 70m in 1x12hour shift, hardrock TBM in sand stone – usually after such records the following shift cleans up! Recent applications of TBMs in mining include projects in Indonesia, South America and the USA.
Shaft or decline? T e advancement of TBMs and conveyor technologies has combined to form a competitive option for mine development both underground and from surface. Conveyors are able to operate around curves and TBMs can be designed to negotiate tighter radius curves. According to my records, the tightest radius negotiated by a hard rock TBM is 20m – the design was for a U turn. As a general rule of thumb for tunnels in rock shorter than 1,500m, drill & blast is the more economical option. So how much does a TBM cost? Last time I was looking, the average cost for a TBM in the 6.5m diameter size range, confi gured for mixed ground conditions was around US$8.5 million. Recent studies have shown that an economic alternative to a 1,200m deep shaft is an 8km
decline at an inclination of 18°. T e pre- feasibility study indicated that considerable CAPEX savings of up to 30% plus a reduction in execution time of 25% was possible compared to the traditional shaft sinking methods.
T e advantage with a decline is that the
services and transportation infrastructure is installed as the excavation proceeds. Service conduits, pipes and power cables utilised in the decline construction can later be used by the mine. In zones of challenging ground conditions pre-cast concrete lining can be installed. T e dismantling of the TBM can be further facilitated by being specifi cally designed for easy disassembly. With the focus these days on cost reduction
and pressure to obtain a faster return on one’s investment, the use of TBMs should be revisited. Alternatively, the shaft sinkers have to tighten their belts and up the pace. ‘What about mechanised shaft sinking?’ I hear some ask – well that in itself is worthy of a separate article. TBM manufacturers currently still operating worldwide; in alphabetical order are: CRTE; Herrenknecht; Hitachi-Zosen; IHI; Kawasaki; Iseki; NFM; Robbins; Shanghai Tunnel Engineering & Construction; and Terratec. ●
For more information ✔ at
www.engineerlive.com/ime
Martijn-K Mannot-Russell is with BASF Construction Chemicals Europe.
www.basf.com
www.engineerlive.com 39
The advancement of TBMs and conveyor technologies has combined to form a competitive option for mine development
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