Fighting Mud in the Poconos

In the Pocono Mountains resort area in eastern Pennsylvania, pipeline construction companies normally have to look for work in other regions during the typically harsh, snowy winters. But, because of El Niño's warm, wet weather blasts coming with the southwest winds during the winter of 1997-98, the crews of Linde Enterprises, Inc. of Honesdale, Pennsylvania, were able to get ahead of schedule on a major sewer-line installation project. The problem now wasn't snow and frost, but mud and water-lots of it.

Tobyhanna Township is located just north of the famous Pocono International Raceway near I-80 in eastern Pennsylvania. The township acquired state infrastructure funds though the PENVEST lending authority to build a sewer treatment facility and sewer system that would support new home development in this picturesque and populated resort area.

Linde Enterprises's crews were charged with placing 17 individual casings under state highways 115 and 940. These casings would carry gravity sewer and forced sewer mains. The first of these was a 36-inch diameter casing that was to carry a gravity sewer line at a precise six-tenths of a percent downgrade over the 50-foot run under Highway 115.

According to Paul Fedor, Linde Enterprises's maintenance supervisor and equipment manager, the wet weather delivered pluses and minuses. "We've had plenty of jobs running at full speed. We were able to get a start on some jobs that we didn't think we could get to until spring," stated Fedor. "But the rain slowed us up some. Take these casing installations for example. There was plenty of dewatering that we had to do in the launch pits."

This first casing installation was done in wet, sandy gravel, typical soil conditions for the region. "Digging the launch pit was the biggest headache," described Fedor. "The wet gravel made digging difficult. We were eight feet below the road surface and the wet gravel and rainwater wanted to roll down into the launch area. The water kept washing down the sides of the pit making it difficult to pump the water out fast enough. We brought in shoring and some rock. That at least allowed us to get the launch area prepared."

Linde Enterprises chose to use the 16-inch HammerHead Mole to ram in the half-inch thick wall casing under the highway. The 50 feet of casing were rammed in using three segments, two 20-foot pieces with a 10-foot pipe length in the middle.

"Linde Enterprises has more than 35 years of experience in this area," explained Fedor. "Normally, we would have considered using conventional auger boring. However, the PENDOT authorities were leery because of all the rain and the possible voids that might have been created under the road. We looked for an alternative. Pipe ramming with pneumatic tools is relatively new to our area. The success we had with this technology enabled us to use it on all 17 of the casings for this sewer installation project."

To prepare for the pipe ramming, the launch pit was carefully graded. Base rock and wood support beams were put in place to support the casing as it was rammed open-ended under the road. A half-inch lubrication line was welded atop the first casing in order to pump a solution of polymer and condet to the inside and outside of the soil shoe. The soil shoe was welded to the lead casing. Not only did this lubrication mixture make ramming easier, but it also kept the spoil inside the pipe in a movable state so that it could be removed from the pipe more easily with compressed air once the ram was completed.

A 36-inch adapter ring and 24-inch collets were set into the casing and the16-inch HammerHead pneumatic tool taper was locked into them. The crew's constant dewatering to keep the rains of El Niño out of the launch area and the welding of the casings lengthened this ramming to two days. The total ramming time during this stretch lasted only 1 1/2 hours.

"The actual ramming time was impressive," said Fedor. "And when the casing came out on the other side exactly on grade, my crew was even more impressed. In these soil conditions, it was much more successful keeping to grade than conventional auger boring would have been. It convinced us that it was able to ram the casing in on grade better than what we had been doing in the past and it's a lot faster."

"We think the productivity of pipe ramming with the HammerHead tool is superior to that of conventional auger boring by 60 to 70 percent in the right soil conditions," described Fedor.

"There's far less labor and material time since we don't have to pour and cure a concrete launch pad. The maintenance difference was obvious to us from the beginning. Our experience with conventional auger boring is that you have to bear the costs of the wear and tear on carbide teeth, flight cutters and augers. With the pneumatic tool, the maintenance is virtually zero."

The population in the Poconos will be growing even more with the addition of this new sewer infrastructure. Land development companies are on the phone with people who are interested in building vacation homes in the Poconos.

Written By: Richard Yach - Technical Writer Des Moines, Iowa
Provided By: Vermeer Manufacturing Company - Pella, Iowa