Tunneling Technology Bores Ahead

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

The tunneling industry's toolbox continues to expand with improved machine design and a wider range of products

Simplicity, capacity, safety and speed-qualities that could be considered the collective holy grail of mine production equipment-are equally applicable to tunneling applications. Whether the tunnel project at hand is a drill-and-blast job or a directly excavated face, the underground equipment and products available today can provide efficiency and reliability comparable to levels generally associated with surface mining. Although size is always important in the cramped world of underground construction, tunneling iron has benefited from technological advances that often first appeared on manufacturers' larger flagship surface units.

Major equipment builders such as Caterpillar or Liebherr have taken dual routes in their underground product line development; in some cases adapting standard surface designs for underground applications, while in others designing application-specific models that nevertheless include a high level of already field-proven components. Both Cat and Liebherr now list specialized tunneling hydraulic excavators and wheel loaders in their respective product lineups, which feature additional vital-component guarding, structural reinforcement, and other modifications for underground use. Optional features such as quick-change tool handlers and side-dumping buckets, available both from OEMs and independent suppliers, also allow conventional wheeled and tracked equipment to maneuver and multi-task more conveniently in tight tunnel environments.

In this article, E&MJ samples some of the latest developments in tunneling technology and its applications, starting with the most basic of underground tools-drills and pumps.

A Big Push on Drills

Based on a solid and simple design, Atlas Copco Construction Tools' pneumatic rock drills and pusher legs offer high reliability and performance for a variety of rock drilling applications, including driving drifts and tunnels with small cross sections.

Atlas Copco provides three families of rock drills: BBC, BBD and RH. The drills weigh between 49 and 68 lb (22 to 30 kg), offer stroke lengths up to 3 in. (7.6 cm) and impact rates up to 55 Hz.

Designed for medium to hard rock between 100 and 400 MPa, the BBC units are the largest of the product line. The BBC drills feature long strokes and rifle bar rotations located in the rear of the drill to provide optimum impact energy per blow. Large-diameter pistons make the units extremely efficient even with decreased air pressure.

To achieve a high impact rate, the BBD rock drills feature ratchet wheel rotations located in the front of the drills, while short strokes ensure high impact energy per blow. BBD drills are also designed with large-diameter pistons for increased efficiency with low air pressure. They are suited for use on medium-hard and fissured rock between 100 and 200 MPa. Additionally, the BBD 46WR model features clockwise rotation for tightening nuts when roof bolting.

The RH drill is the smallest unit, weighing 49 lb, but Atlas Copco claims that its rifle bar rotation, high penetration and low air consumption make this drill efficient, powerful and ideal for use with soft to medium rock between 100 and 200 MPa. Because of its light weight, the RH rock drill is also useful as a sinker, and a T-handle can be used in place of a pusher leg.

Atlas Copco also offers three families of pusher legs: BMT, ALF and BMK. The BMT and ALF series match with the BBC and BBD drills and feature lightweight designs and double-acting feed legs with aluminum cylinders. The BMT and ALF series can extend more than 10 ft (3 m) in length and offer a feed length of 37 to 51 in. (94 to 130 cm).

Also available for BBC and BBD drills is a telescopic pusher leg with a double-feed cylinder, which provides a feed length of more than 73 in. (185 cm) and a length of approximately 11 ft (3.3 m) when extended. The telescopic pusher leg is ideal for drilling at height or performing applications that require extra feed.

The double-acting BMK pusher leg is compatible with the RH rock drill and features a pushbutton release valve that quickly retracts the feed on the leg. The BMK is more than 10 ft long and has a feed length of 51 in.

For larger drifter and tunneling drills, Sandvik Tamrock Tools has developed drill bit and steel product lines that offer improved performance through computer design optimization and higher rod stiffness. Sandvik's CAPP standard bits for drifting and tunneling, for example, include hole diameters from 35 to 51 mm. The CAPP line-CAPP refers to the computer-aided design and production process used to develop the family of bits-features diameters, threads, bit front designs, gauge and front inserts, flushing configurations, insert shapes and carbide grades as well as other components "matched for optimal performance," according to the company.

Tamrock's Alpha 330 45-mm-diameter drilling tool system features a stronger and more rigid thread that is only 1 mm larger in diameter but with a 14% larger cross-section than R32 drifter rod. To further improve rigidity, Sandvik introduced a new guiding function between the rod and bit skirt. In addition to reducing the risk of bending, the bit skirt covers the thread to reduce the risk of corrosion fatigue. A stronger connection between the rod and bit results in a significant drop in the overall frequency of breakages. This tool economy, together with more accurate collaring and straighter holes to give better fragmentation and improved profile control, can reduce the overall cost of drifting and tunneling.