Tunneling Technology Bores Ahead

Engineering and Mining Journal, Dec 2005 by Carter, Russell A

Since the crawler excavators and wheel loaders are working a two-shift operation in a tough environment, the joint-venture equipment team paid particular attention not only to specification but also to technical support and service arrangements. "We were already in contact with Liebherr-Mietpartner and CoMat (the Liebherr dealer in Luxembourg) concerning specifications and technical support for the machines several months prior to the start of construction," said Fercher. The machines will be serviced and technically supported by CoMat during the entire construction period. The joint venture's 30-person technical crew will support the CoMat team whenever necessary.

Fans Under Finland

The Fläkt Woods Group, formed in 2002 when Global Air Movement SARL merged Svenska Fläkt and UK-based Woods Fans, is a global supplier of ventilation equipment for the surface construction and tunneling industries. The group recently supplied about 300 fans for the ventilation system of a new underground mine at Outokumpu Ferrochrome's Kemi operation in northern Finland.

Here, mining activity extends to a depth of 600 m and good air quality is essential. Kemi's Underground Director, Juha Riikonen, explains: "The need for ventilation is increased by blast gases and the exhaust gases from diesel-powered machinery, as well as by dust generated by drilling, blasting and transporting the blasted rock." Two main 2-m-diameter JM axial fans on the surface supply fresh air for the mine through the ventilation air intake shaft. The fresh air is directed to work areas by local fans and ventilation ducts. Smaller Fläkt Woods fans are used in the roadway tunnels and as local fans at work areas. Other JM axials located throughout the mine infrastructure act as exhaust air fans, directing outbound air to the two exhaust air shafts.

All of the main fans are located on the surface and are controlled by frequency converters. The ventilation control is constructed so that it acts as a part of the mine automation system. Sophisticated system programming takes into account the time of year, blasting schedule and reduced mine operations during nights and weekends.

"The basic requirement underlying fan selection was that the different parts of the mine needed to be supplied with the necessary amount of air at a certain overall pressure. The outside positioning of the fans and the ability to rotate them in the reverse direction in a fire situation were additional requirements. After considering these requirements and the total economic impact, we ended up choosing Fläkt Woods' products," explained Juha Riikonen.

Liner Plates: Soft Sell

Steel liner plates provide a relatively lightweight, easy-to-handle, safe support for soft ground tunneling because the ground that supplies the loading also supplies the resistance to the load. Virginia, USA-based American Commerical Inc. is a leading supplier of liner systems, which can range from liner plates only, to steel ribs inside liner plates or liner plates installed between ribs.