Edward McGinn General Contracting Inc. had to fight the rain, the tides and the moon as it bored a tunnel beneath the Chester Creek in Chester, PA, and laid sewer pipe, but in the end, they were successful.
“We had 120 days to do the project. We started the first week of September. It looks like we’ll wrap up about one month ahead of schedule,” said Michael Kerr, project manager of McGinn.
In a nutshell, the project, as described by McGinn, was laying 450 ft. (137.2 m) of 36-in. (91.4 cm) TR Flex sewer pipe beneath the Chester Creek. The owner of the $950,000 project is the Delaware County Regional Water Quality Control Authority, otherwise known as DELCORA.
“It was tried by another contractor at least one time before, but they could not even get going on the job. The way the project is designed makes it difficult. You are working so close to the water — within 20 ft. of the edge of the river — that it was tough keeping the water out,” John McGinn, owner, said.
The first step was digging the 40-ft. (12.2 m) deep bore pit on one side of Chester Creek and the 40-ft. (12.2 m) deep receiving pit on the other side of the creek.
It took two weeks to dig each of the pits.
McGinn excavated as much as he could with Hitachi 450, 110,000-lb. (49,895 kg) track hoes. Their 28-ft. (8.5 m) reach made a big dent in the digging.
“The Hitachis are great machines. They have great reach and great capacity. We love them. All our hoes are Hitachis, from Elliott & Frantz,” Kerr said. “The challenge with the pits was getting to the bottom. Standard equipment would not go to the depth we needed — 40 ft. The Hitachi went down to 28 [ft.]. We reverted to the old fashioned way of the clamshell. It was slow, tedious, and monotonous, but we did it.”
Special custom made and engineered shoring from Mabey Bridge & Shore of Elkridge, MD, was used to shore up the pits. Concrete slabs were laid across the bottom of the pits to help provide structural integrity.
“We had them come out a couple of times to make it safe for the men down in the hole Mabey Bridge & Shore stopped by at least once a week while we were digging,” Kerr said. “Tight sheeting and shoring with the Z-lock system was used.”
McGinn had to make changes in the pit layout as the job progressed.
“We started digging the receiving pit as it was engineered, but water starting coming in. It was originally designed next to the bulkhead of the old abandoned bridge — 8 ft. off the edge of the bulkhead. That was just too close to the creek. We had to push it back about 40 ft.,” Kerr explained.
The shoring kept the sides secure, but that was no help against water coming in from the creek once the job started.
“Water seeks the path of lowest resistance and we were only 20 ft. from the edge of the river,” said McGinn. “We lost the bore pit not once but twice because of water infiltration.”
He said divers from Walker Diving, Hammonton, NH, were brought in.
“Water had seeped in and ran along the 48-in. casing. It came in on the bore pit side. The divers pumped grout in on the bore pit side. It solidified wherever there were voids and we managed to control the water,” said McGinn.
But, then the rains came and the creek levels rose. The job site is within 1,000 ft. (304.8 m) of the Delaware River so tides were a problem as well.
“There was a 6-ft. rise and fall with the tides. That put a lot of stress on the equipment and the work as we progressed,” said Kerr.
John Fithian Contracting, Youngstown, OH, which McGinn has used on other jobs, was called in to do the boring. Fithian was running an around-the-clock bore.
“Two or three o’clock one morning, the water started coming in pretty hard. The creek actually overflowed its banks. We got pumps from Godwin Pump of Bridgeport, NJ. We had pumps running around-the-clock. At one point, the water was up and over the top of the bore pit," Kerr recalled.
“With Godwin’s help, we were able to get water down. The pumps proceeded to keep the water down so we could get the bore all the way across to the receiving pit,” Kerr said. “The pumps were outstanding. Mike Delzingaro, Godwin’s sales manager swung by the job everyday to make sure everything was running OK.”
The pumps, along with Fithian’s rockhead drill bit, were the stars of the show.
Godwin supplied McGinn with three Heidra 15 6-in. (15.2 cm) pumps and one Heidra 200 8-in. (20.3 cm) hydraulic submersible pump. They were used to dewater the boring pit, so that the contractor could work in a dry area.
On the receiving end, a CD150 6-in. (15.2 cm) Dri-Prime pump was used to bypass a tidegate to feed into the pit. A Heidra 100 4-in. (10.2 cm) hydraulic submersible pump was used to dewater the pit.
Because there was no on-site power, Godwin’s diesel pumps were ideal. In addition the boring pit was 36 to 38 ft. (10.9 to 11.6 m) deep which meant that a submersible unit was required.
“We don’t have problems. We have solutions. This was a unique project. We took over a project that someone else started but didn’t finish. It made it more of a challenge for us than other jobs,” said Kerr.
“It was definitely a learning curve for us. We learned a learned a lot on this. It was exciting, challenging, and exhilarating. Eleven contractors picked up plans, but only two ended up bidding on it,” said McGinn.
Explosives and a rockhead drill were used to lay a 48-in. (122 cm) casing beneath the creek, then the 36-TR Flex pipe was brought through.
’There was clay and alluvial soil on the bore pit side so we had an easy start. Then we ran into solid rock as we tunneled across the river. We ended up using Explo-Craft of West Chester as the blasting contractor. We had to drill and shoot — lay dynamite and break rock up,” Kerr explained.
Even when the auger had made it through to the receiving pit, the job still was not over. They had to gingerly work to remove the drillhead.
“The auger got off-center just a tad. It made it through to the receiving pit, but got wedged in rock. We had to hand-drill and split the rock to get the bore out,” said Kerr.
“Fithian is the best. They have the expertise and the knowledge for a project like this. That’s why we went with them. Everyone worked together on this job, just like a team rowing sculls on the Schuylkill. It was a difficult job, but no one got hurt. It was challenging but we were all up to the challenge,” said McGinn.
“They just finished pressure-testing the line and it passed. All that is left is the restoration. It is 100-percent complete and we got the job done ahead of schedule. We started the first week in September and were given 120 days to do the project. It’s done,” said McGinn.