Limestone Could Not Stop

Solid Limestone Could Not Stop Piercing Tool

In March 1996, Pennsylvania American Water Co. (PA-American) had nine crews armed with piercing tools installing water mains beneath roadways in a primarily rural area. The objective was to connect approximately 450 new services. Soil components were expected to be mostly clay, occasionally mixed with rock.

However, it was not expected that a crew would encounter a solid wall of limestone when performing a short bore.

Demo Requested

Limestone Could Not StopAlthough PA-American already owned several piercing tools, the company needed to add to its fleet to accomplish these water-line installations in a timely manner. This was the opportunity that 247 Equipment Co. sales manager Mike Schultz had been waiting for. 247 Equipment is an equipment sales and rental operation based in Eighty Four, PA.

Schultz received an initial request from Bill Daschbach, operations manager of PA-American’s office in Bethel Park, PA, for a demonstration of a Grundomat piercing tool with its patented reciprocating head. The Grundomat is manufactured by TT Technologies, Inc., Aurora, IL.

Schultz arranged the particulars with Dave Benz, purchasing agent in the Bethel Park office. Based on the background information provided, Schultz supplied a 3-in. piercing tool from the company’s rental fleet. The tool came with 50 ft hose and in-line lubricator.

On Site

While PA-American crews had prepared the entry area, they discovered that the sand and clay soil was peppered with an unusually high concentration of rock. What they didn’t know was this was only a forecast of what was waiting ahead.

Once the piercing tool was launched for the 25-ft bore, crews moved to the other side of the road to prepare the exit area. There, they quickly discovered the shelf of limestone. A jackhammer was used to create an exit area for the tool.

Even with this seemingly impenetrable obstacle ahead, the piercing tool was left to continue the bore as a test of its tenacity. At around 23 ft, the tool slowed dramatically, yet it continued to make progress. PA-American’s crew chief Tony Cappetta estimated at that point there was 12 to 18 in. of limestone between the tool and blue sky.

Crew members and onlookers were amazed when the piercing tool’s chisel tip first chipped through the stone in the exit pit. “Just two and a half hours from the time we started the tool until it poked its head out the other side,” Schultz said. Normally, this type of short bore can be completed in 20 to 30 minutes.

The amount of rock restricted the area of the exit pit, not allowing enough room to remove the tool. Crews backed out the tool, slid a 3/4-in. copper pipe into the bore and tapped the pipe.

Reciprocating Heads

Grundomat pneumatic piercing tools have a reciprocating stepped-cone head for power and accuracy. The tiers of the stepped-cone head act as a stabilizer through an assortment of mixed soils. The reciprocating chisel tip functions like a pneumatic hammer, breaking up obstacles in the path of the tool.

To aid in a successful bore, TT Technologies’ in-line lubricators provide a pre-established amount of bio-degradable pneumatic tool lubricant to properly mix with the compressed air as it enters the piercing tool. Pneumatic piercing tools perform better and require less maintenance when the piston/cylinder combination is well lubricated during use.

Reactions And Response

When the eight other PA-American crews heard about the successful bore, they stopped by the site to see it for themselves. “Everybody was amazed,” Schultz said.

One PA-American employee kept the piercing tool in his car for the next two weeks because he “didn’t want anyone else to use it.” PA-American crews traditionally perform bores through difficult soils with auger boring machines. The uncommon soil conditions in the area of the isolated bore allowed the piercing tool to demonstrate its full potential.

As in most trenchless boring operations, tools are selected based on apparent soil conditions.

“In no way could we envision what was going to happen,” Schultz said. “But it couldn’t have gone any better.”

Jim Johnson is a writer for Lime Valley Advertising, Inc., Mankato, MN.


by Jim Johnson

Trenchless Technology, July 1996, Page 37