A River Runs Around It: Whitaker Construction Diverts River and Builds Cofferdam using Efficiency Production Trench Boxes

 The swift currents of the Weber River in Riverdale, Utah, are perfect for fishing.  Trout and Whitefish; both are active and plentiful in the quick currents.  The river is a sportsman’s paradise, but a real headache for the Central Weber (Utah) Sewer District. 

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

 Experience matters

On the third occurrence of sewer pipe trouble–this time in Riverdale, Utah–the Sewer District let the $600,000 Weber River Sewer Crossing Rehabilitation project to Whitaker Construction Company of Brigham City, Utah.  Whitaker Construction Company had previously repaired a similar sewer line in a different area of the Weber River, and was familiar with the challenges of accessing under-the-river sewer pipes.  The engineer for the project was Greg Poole from Hansen, Allen, and Luce, LLC; and 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 in. pipe encased in 4 ft. poured-in-place cement.  A diver was called in to inspect the pipe and make a recommendation.  Whitaker decided to dam the river, allowing them 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 Company Supervisor Brian Hamson, trench boxes were more cost effective and they also created less dirt and silt in the water.

After a bypass channel was dug and shored, four 8 x 20 ft. Efficiency Production, Inc. trench boxes with 84 in. 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 x 20 ft. dirt-filled trench boxes also 7 ft. 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 in. electrical pumps, each with a capacity of pumping 1,600 gallons of water a minute.  In total, 525 ft. of the river was closed off and diverted.

 Whitaker then dug four feet into the riverbed to get to the pipe, and shored that cut with steel sheeting driven 17-18ft. below the encasement.  The pipe and 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 they 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 their 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 x16 ft. I-beams.  Their equipment included three excavators, a Volvo 360, a CAT 330, and an Hitachi 300; two Volvo 120 front loaders, and two 7-yard Efficiency Production Stone Mizers.

Efficiency 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," said 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 ft. high trench boxes were set with 16 ft. wide spreaders and lined with 1/32 in. Polypro-Olin sheets.  A combination of 10, 12, 16, and 20 ft. long trench boxes were used for a total length of over 300 ft. of “shielded” channel.

The channel was designed so that 5 ft. of water would pass through the boxes, which in normal conditions would carry about 600 cubic ft. per second (cfs.) of water flow within the inside of the trench box walls.  Because of increased water flow due to rain and flood waters, however, the actual water flow pressure was greater than 1,350 cfs. 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,” said 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,” added Hamson.

Day was quick to credit Whitaker for their 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 Company have found many creative uses for Efficiency Production Inc. trench boxes and Slide Rail System over the years.  “Other companies that we work with are not real eager to help when we have requirements that are beyond the normal use of their particular product,” said 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 riverbed.

Restoration was a simple reversal of the set-up 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 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.

Whitaker Construction Company

The waters of the Weber River were diverted through trench boxes for 325 ft.; longer than a football field!	Whitaker built a bridge over the bypass channel using 20 I-Beams supporting an 8 in.-thick trench box wall.
The 18 ft. wide trench boxes in the diversion channel were designed to withstand 600 cfs. of flow from the 5 ft. of water. Because of rain and flooding, the boxes withstood more than 1,300 cfs. of flow with no problems!	Whitaker Construction Company used a cost-effective cofferdam system…trench boxes manufactured by Efficiency Production, Inc.
A 14 in. cross-utility sewer pipe is repaired, and the 4 ft. pour-in-place cement encasement is built-up and protected with boulders.	To control the fast current of the Weber River, Whitaker Construction added rocks and boulders to the riverbank and bed to act as a “waterfall,” decreasing the speed and destructive hi-rate of erosion.