Whitaker Construction diverts river and builds cofferdam using Efficiency Production trench boxes.

By James McRay

The swift currents of the Weber River in Riverdale, UT, are perfect for fishing. Both trout and whitefish are active and plentiful in the quick currents. The river is a sportsman’s paradise but a real headache for the Central Weber Sewer Improvement District.

On three occasions, the district has needed to rehabilitate utility pipes that run underneath the river because the swift current keeps eroding the riverbed and exposing the sewer lines, potentially causing leaks and cracks.

Experience Matters
On the third occurrence of sewer pipe trouble—this time in Riverdale—the sewer district let the $600,000 Weber River Sewer Crossing Rehabilitation project to Whitaker Construction Co. of Brigham City, UT, 60 miles north of Salt Lake City. The company has been in the underground utility business for more than 50 years and is still family owned by brothers Bob, Dennis, and Rick Whitaker. Having previously repaired a similar sewer line in a different area of the Weber River, Whitaker Construction Co. was familiar with the challenges of accessing under-the-river sewer pipes. The engineer for the project was Greg Poole from Hansen, Allen & Luce LLC; the project inspector was Paul Higgins.

Assessing the Situation
The first step for the sewer district’s project engineer was assessing the condition of the 18-inch pipe encased in 4-foot poured-in-place cement. A diver was called in to inspect the pipe and make a recommendation. Whitaker decided to dam the river, allowing the crew to be completely unencumbered while repairing the pipe.

Damming the river also gave them the opportunity to work at controlling the river’s flow. Boulders and large rocks were placed just below the natural waterline of the river to act as a “waterfall” for the current, decreasing its speed and slowing the erosion.

Cost-Effective Trench Boxes Used as Cofferdam
Rather than utilize an expensive cofferdam system, Whitaker used a much more cost-effective system to dam the river: trench boxes manufactured by Efficiency Production Inc. According to Whitaker Construction Co. Supervisor Brian Hamson, who has been with the company for 33 years, not only were trench boxes more cost-effective; they also created less dirt and silt in the water.

After a bypass channel was dug and shored, four 8- by 20-foot Efficiency Production trench boxes with 84-inch spreaders were set upstream in the river one at a time and then filled with dirt to create a solid cofferdam. Downstream of the work area, three 8- by 20-foot dirt-filled trench boxes 7 feet wide dammed off any backflow of the river. Once the river was diverted through the bypass channel, any remaining water in the dammed section was then pumped out with three 6-inch electrical pumps, each with the capacity to pump 1,600 gallons of water per minute. In total, 525 feet of the river were closed off and diverted.

Whitaker then dug 4 feet into the riverbed to get to the pipe and shored that cut with steel sheeting driven 17 to 18 feet below the encasement. The pipe and the encasement were checked for cracks and repaired where necessary. The encasement was then covered and built back up with boulders to add to the protection of the sewer pipe.

Overcoming Access Challenges, Diverting the River
Damming the river was only part of the challenge. The river’s swift waters needed to be diverted to a point downstream of where Whitaker crews were working on the sewer pipe. Normally, an open bypass channel would be excavated on one side of the dammed river, and the work would be performed from the other riverbank. This section of the river, however, had a railroad yard bordering tightly to the east side of the river’s edge, completely eliminating access from that direction.

Whitaker had no choice but to run the diversion channel around the west bank of the river and bring all its equipment and supplies onto the “island” that was created between the diversion channel and the dammed river section.

To get to the island, Whitaker built a bridge over the diversion channel using a trench box wall supported by 20 16- by 16-foot I-beams. The equipment included three excavators, a Volvo 360, a Cat 330, and a Hitachi 300; two Volvo 120 front loaders; and two 7-yard Efficiency Production Stone Mizers.

Efficiency Production Trench Boxes the Solution Again
Whitaker had more concerns with the bypass channel. “There is so much development in that area that we had to keep the channel relatively close to the dammed section of the river,” says Hamson. “But we were concerned that the current could expand the channel so quickly that we’d have no room to work.”

To control the flow of water through the diversion channel, Whitaker lined the channel with 33 trench boxes from Efficiency Production Inc. and others. The 8-foot-high trench boxes were set with 16-foot-wide spreaders and lined with one-thirty-second-inch Polypro-Olin sheets. A combination of 10-, 12-, 16-, and 20-foot-long trench boxes was used for a total length of over 300 feet of “shielded” channel.

The channel was designed so that 5 feet of water would pass through the boxes, which in normal conditions would carry about 600 cubic feet per second of water flow within the inside of the trench box walls. Because of increased water flow due to rain and floodwaters, however, the actual water flow pressure was greater than 1,350 cubic feet per second of flow, well past the rating of the boxes; yet the boxes withstood the flows with no problems.

 “We use Efficiency trench boxes a lot, and they have always worked very well for us. Over the years, we’ve come up with a lot of different uses for them,” says Hamson. “We’ve rented a lot of these boxes from Jeff Day at United Rentals Trench Safety in Salt Lake City, and he has been wonderful helping us find solutions to our sometimes unusual challenges,” he adds.

Day was quick to credit Whitaker for its ingenuity: “It was pretty impressive seeing all that water running through those trench boxes,” he says. “Whitaker Construction has just been fantastic to work with, and their staff is second to none.”

The contractors and engineers at Whitaker Construction Co. have found many creative uses for Efficiency Production trench boxes and Slide Rail Systems over the years. “Other companies that we work with are not really eager to help when we have requirements that are beyond the normal use of their particular product,” says Hamson. “Efficiency is always excited and ready to help design or engineer creative solutions for their trench boxes, and that makes our job so much easier.”

Timeline
In took Whitaker just one week to cut the bypass channel and dam the river, and then seven weeks—January 5 through February 17, 2005—to complete the rehabilitation to the pipe and the riverbed.

Restoration was a simple reversal of the setup process. The downstream cofferdam was removed first, one trench box at a time, and then the upstream cofferdam was pulled out. For a period of time, water flowed down both the river and the bypass channel. Whitaker then closed off the upstream mouth of the diversion channel, returning the flow of the river to its original course. After pulling the trench boxes from the bypass channel, it was backfilled to complete the restoration of the area.

Author James McRay is with Efficiency Production Inc.

GEC - January/February 2006