When the quartzite quarry that supplies rock products for Concrete Materials was established in the early 1900s, it was nowhere close to the Sioux Falls city limits. However, over the past 100 years, the sprawl of urban growth has reached beyond the quarry, and the company finds its quarry and the asphalt and concrete plant well within the city limits of South Dakota's largest metropolitan area.

A steel shell surrounds Concrete Materials' screening towers to help control dust and protect the close residential and business neighbors who have sprung up around the rock quarry.

Concrete Material's Aggregate Division manager, Jon Mulloy, said the company has adjusted its operations in recent years to minimize the impact of their work activities on the neighboring residents and businesses. They have been successful in that venture and in improving their own work process.

"About 20 years ago, our haul route took our trucks across Madison Street, one of the city's main thoroughfares," Mulloy said. "At that time, it was a two-lane road and our trucks had to yield to oncoming traffic. The route also took trucks up two different lifts, which meant they had an 80-ft. climb to navigate, too."

With increases in both production rates and the time factor involved because of traffic crossing their haul route, Concrete Materials began considering how they could alter their haul process.

"By 1990, we were looking for ways to save both time and fuel," Mulloy said. "Our goal was to eliminate the 80-ft. climb and keep our trucks out of city traffic. If we could find a way to shorten our haul, we knew we would save fuel and time."

Take note

One of the options Concrete Materials decided to explore was the creation of a tunnel to connect their north and south quarries. Blasting through a wall of rock dividing the quarries would make it possible to establish a shorter haul route for their trucks and circumvent traffic.

Correct angle

"We brought engineering specialists in to evaluate the impact a tunnel would have on the quarry," Mulloy said. "Because quartzite is formed in layers, we knew we would have to drill the tunnel at a specific angle so the rock above the tunnel wouldn't collapse. Quartzite layers are very jointed. The rock almost breaks itself into blocks. We had to work with the natural joints in the rock so they would lock even tighter."

Once they had evaluated the impact the tunnel would have on the surrounding rock, the company determined the best location for and angle to use to create the tunnel. The next step was to begin drilling and blasting.

"We drilled and blasted in the daytime," Mulloy said. "At night, we dug the rock out and hauled it away. It all worked very well. The natural joints in the rock lock the tunnel roof in place so securely that there's no need for roof anchors in the tunnel. It supports itself."

After approximately four weeks, Concrete Materials had a tunnel 275 ft. long, 25 ft. wide and 25 ft. tall at its shortest point. Their trucks easily pass through, one at a time, and their haul route was cut in half in terms of its length. The new route doesn't cross any major traffic streams and is actually under Madison Street, which they used to drive across.