SITUATION: To install a new section of water transmission main under the Tittabawassee River for the city of Saginaw, Michigan. The pipe will increase water capacity and reliability of the city’s water transmission system.  It will also serve an adjacent township, another water supply system and a large high tech manufacturer.

 

METRICS: The 2,668 foot section of 24-inch diameter water main is to be installed 30 feet under the river bottom, which reaches a depth of 60 feet in some areas. The pipe string weighs an estimated 300,000 pounds (empty) and is one of the largest horizontal directional drilling (HDD) projects ever undertaken in Michigan. 

 

CONTRACTOR: Spicer Group, Inc., Engineering, Surveying and Planning.

 

OWNER: City of Saginaw

 

CHALLENGE: Completing a water main bore and pulling a pipe string of this size and length always presents extraordinary tests of equipment, the drilling team, and the coordination/timing required to meet deadlines.

 

 

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AS holders of the world record lateral HDD crossing, Environmental Crossings, Inc. is justifiably proud of its seasoned drill teams, equipment and reputation. Nevertheless, accomplishing this installation in a single pull, ahead of schedule and on budget, were benchmarks never far from the minds of the ECI construction superintendent, drill team and engineers staffing the project.

 

For starters, the team drilled 2,688 feet of 6-inch steel drilling rods under the river, then connected the string to 2,688 feet of 24-inch HDPE (high density polyethylene) pipe. This was fused using thermal welds and strung along a road adjacent to the drill pit. The entire chain stretched for over a mile, and closed an intersecting road, along with the driveways of several businesses. The above-ground rigging provided prime spectator fare, as well as inciting plenty of coffee klatch speculation by the neighborhood’s sidewalk superintendents. 

 

The pilot bore was the easy part. Once the 6-inch drilling rods had broken through on the other side of the river, a reamer was attached and pulled back through the pilot hole. This increased the size of the bore hole to 36-inches. The void was packed with bentonite (aka Wyoming Clay) drilling mud to keep the hole open, while continually pumping out the used drilling mud into reclaimers. This process separated the solids from the mud, allowing recycling and reuse of the material.

 

After the hole was reamed, a swab was pushed through it to smooth the walls and clear debris. And again, the bore hole was pumped full of bentonite drilling mud.

 

ECI’s drill team then connected the drilling rods to a 30-inch pulling head fused to the HDPE water main pipe---and pulled the 2,668-ft. section of pipe though the hole.  Drilling mud displaced by the pipe during the pull was captured using large mud pumps and vacuum trucks. Pumped into huge holding tanks, it was later disposed of.

 

“The actual time it took to pull the pipe was only about six hours,” explains Philip Andrus, president of ECI. “When you stop to think about pulling that weight (300,000 pounds) and a 2,688-ft. pipe string, that is quite an engineering achievement.”

 

To ensure the project’s success, ECI brought in one of their largest HDD rigs for the heavy pulling. It has a pull-capability rating of 1.2 million pounds.

 

For the record, the entire HDD process took about eight days.

 

“When you consider the number of drills, the length and size of the pipe, and the fact that we did the crossing in a single pull----this is a real testimonial to our experience, equipment, and the efficiency of our drill team,” noted president Andrus.

 

The Tittabawassee River crossing sidewalk superintendents would agree.