Tigard Sand & Gravel is a busy place. Located just outside Portland at Tualatin, Ore., Tigard supplies aggregate for a booming real estate market. An average day can see more than 600 trucks crossing the scales at the quarry, and recently 823 trucks passed over the scales in one day. That's one truck every 20 seconds.

The quarry sells 13 types of aggregate material. Tigard's products are used for everything from road base to asphalt production. Two crusher systems separate various sizes of material with one dedicated to asphalt production and the other for general aggregate use.

To keep up with the production, Tigard's quarry superintendent, Steve Bennett, has moved two older ECM 370 air drills to backup duty, and purchased a ROC D5 for production drilling.

"The drillers think they've died and gone to heaven," said Bennett. Moving into the ROC D5 has gotten the drillers off their feet and into a climate-controlled cab. Out of the elements, drillers can more easily concentrate on their work.

"With the new MSHA rules it made sense to move to a cabrig," noted Bennett, citing silica dust and high decibel levels as potential problems for drillers.

Increased production

Left to right: Mike Dukart, sales manager for Modern Machinery; Steve Bennett, superintendent at Tigard Sand & Gravel; Clint Byington, district manager for Atlas Copco; Rob Jacobs, salesman from Modern Machinery and distributor for the territory.

Joystick controls and electric over hydraulic automation has provided additional benefits. Higher operational speed has increased production levels because one drill is completing the work of the two older drills. Bennett said, "The drillers love the automation, and they all think it's pretty cool."

To meet the demand, Bennett said they "drill 1,200 to 1,500 ft. a day for a 10,000-to 12,000-ton blast." The drilling is anything but straightforward in this quarry. Just looking at the high wall it is easy to see how each stratum in the formation varies. The face shows thick solid layers varying in depth separated by unconsolidated rock.

"Every layer causes another problem," said Bennett. In solid rock, there can be fracture problems causing large boulders, and soft rock causes drilling problems. Bennett wants others to consider the unconsolidated rock in their area when purchasing a rig. He said loose rock could cause problems for the driller, resulting in jamming in the hole from caving rock. To compensate, Bennett said it is necessary to put more air to the hole to keep it clean.

He said that in solid rock there is never a problem. In hindsight, he thinks going with the ROC D7 may have taken care of this issue because of the larger air package, 152 psi/223 cfm versus the 123/180 on the D5, but if the driller is careful in those areas, he gets by without too much of an issue.

Measuring the blast

The formation at Tigard goes from a solid to unconsolidated rock, making the drilling more of a challenge for the operator.

The rock taken at each level is used for different purposes so it is generally removed one layer at a time. Bennett said the deepest they will take a shot is 60 to 80 ft. This is to reduce noise and vibration, as much as anything, as a housing development has cropped up near the pit.

In the surrounding neighborhood, Tigard Sand & Gravel has located six seismography machines to measure the blast.

Bennett said he got a call from an angry neighbor after a shot saying she had just moved in and the realtor told her that the quarry had been abandoned for years.

Bennett suggested she call her realtor. The truck traffic in and out of the quarry alone is like a beacon pointing to this quarry that has been in operation for decades as the city has grown around the site.

Because of the hardness of the rock, Bennett said they had to go to T-45 steel. They started out with T-38, but the steel wasn't holding up to the conditions.