Boring Through Hardpan Pneumatic Tool Completes Project in Adverse Soil Conditions

August 18, 2017

Most of us don't have the chemistry background to understand the ingredients in a microwave dinner, much less the contents of an industrial solvent. But it's a sure bet that the residents of Grant, Mich., have learned all they'll ever want to know about TCE, or Trichlorethylene, an industrial-strength solvent that leached its way into the town's water system, forcing residents to resort to bottled water for the entire summer of 1995. 

Located in western Michigan, just south of the Manistee National Forest, the town of Grant was shocked when the water system was despoiled. However, city leaders wasted no time in capping the old wells, digging new wells outside of town, and contracting the installation of house service lines as quickly as possible. So the chosen contractor, Montgomery Excavation, and its subcontractor, J. L. Fisk Excavating of Perrinton, Mich., experienced a sense of urgency in getting the water lines in. 

Fortunately, J. L. Fisk Excavating has a 25-year history of working in Michigan's variable soil conditions, so the project was well-matched with the company's experience in installing water and sewer systems. From April to October of 1995, Montgomery's and Fisk's crews labored to install eight-inch and 12-inch main lines, and one-inch to two-inch copper house service lines to over 290 residences in contaminated areas. The placement of an estimated 17,000 feet of service line was completed October 4 when the last line was tied into the town fire department. 

Throughout the installation period, Fisk's crews worked feverishly, often past sundown. Not only did the crews tie in the house drops to the main water lines, they also bored under the properties and made the water connections inside the residents' houses. 

According to job superintendent Lee Fisk, the difficulty was compounded by the soil conditions. "This area has extremely variable soil conditions. East of town, where a lake was drained many years ago, is low land that vegetable farmers use," he explained, "But in town where we did most of the work, we found a hardpan clay that was as close to rock as I have ever seen." 

The Newaygo County Soil Conservation Service described the conditions Fisk's crews were boring in as Marlett - striated soil layers consisting of a top foot of dark gray loam, a layer combined of mottled clay and sand, and, finally, a subsoil of firm clay. According to Lee Fisk, the word firm does not adequately describe this hardpan. 

"We were potholing to find our tie-in sites to the main lines with a CAT 436 backhoe," he stated. "And we could not take out any more than a scant six inches of earth with any bucket load. That's how hard it was in some places." 

Productivity was slow going most of the spring and summer, with Fisk's crews installing house lines with pneumatic tools. Fisk became impatient with the low productivity. "Sometimes, we could get only from one to six inches a minute," he lamented, "The ground would glaze around the bore like it had been in a kiln. The smooth-headed tools would not grab and hold their position, but would recoil and slide back." 

Fisk started using a three-inch HAMMERHEAD MOLE® with a gumbo nut replaceable head around mid-August, and his productivity soared. Originally designed for soft, nonplastic, less compactible conditions, the replaceable head for the three-inch pneumatic tool worked well in this tough clay. 

The gumbo nut tool head has a tapered stair-step design, with the underside of each "step" undercut like the barb on a fishhook. As the striker hits the front anvil and drives the tool into the soil, the clay molds itself around the "barbs" and holds the tool in place. A small amount of anchoring force is enough to assure the forward movement of the tool. 

"Once I had this HAMMERHEAD MOLE, I left the gumbo nut on and used it in all the shots, regardless of the soil conditions. You have to understand, this ground was a real bear, and this tool was the only one that went anywhere," exclaimed Fisk. "We used it for shots from 30 feet all the way up to 100 feet, and because of it, we were able to get the job done and get these folks their water system back."