GSW Goes Small To Conquer Rock

March 2011, Vol. 66 No. 3

Cavalry
After the rock formations had defeated previous invasions initiated by another contractor using a larger drill and experimenting with various drill bits, Infrasource turned to GSW Contracting for assistance. After completing a site evaluation, Wilder’s clean-up crew put their experience to work and took the rock challenge head-on by employing a strategy they had used successfully in similar contests with varying rock formations in the past. After repeated, hard-hitting assaults, ranging from 200 to 500 feet per shot, the rock succumbed. After completing 20 shorter-range bores, Wilder’s crew had prevailed -- void of the muscle most felt was necessary to emerge victorious in similar contests against rock.

“We were drilling on average of 150 feet a day,” Wilder says. “There were times when we had to put on a reamer and pre-ream some of the bores and this slowed our production rates accordingly. But in conditions where we could use the hammer exclusively we were drilling close to 40 feet an hour. That’s not too shabby considering it was solid rock that we were boring through.”

The smaller D20x22 Series II Vermeer drill GSW Contracting used to complete the job had several competitive advantages over the larger rigs that had failed previously; including the ability to use a much smaller compressor to clear the bore of spoil. Wilder’s crew used a 375 cfm/ 200 psi compressor that not only used less fuel to operate than compressors often needed to accommodate larger drills, but by weighing in at only 7,000 pounds, it was also a unit that could be transported on site with a more economical towing vehicle, helping reduce operational costs.

In instances where back-reaming was required, Wilder’s crew used a 6-inch reamer to secure unstable formations resulting from occasional mini cave-ins. As Wilder explains, there isn’t much that equipment, attachment or operator can do to control every bore response in the various rock formations that can result in an unstable bore wall. While unpreventable, these situations still affect overall productivity -- something Wilder encourages other contractors to recognize as part of the rock contest.

“Do the best you can do with the experience of the operator and the capabilities of the drill but recognize that when drilling through rock some things are simply unavoidable,” Wilder says. “The key is to be aware of the variables up front and account for them when preparing the bore approach and most importantly, the bid. Account for what cannot be controlled and tackle the rest in the most efficient way.”