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HDPE Solves Earthquake Damage Problem In Washington State

by Drew L. Wilson

Olympia, WA, is not the ideal setting for a major construction project. The city is located on the shores of South Puget Sound, with the rugged Olympic Mountains rising in the distance across Capital Lake and the dome of Washington State's capitol soaring above the town. However, when an earthquake with a magnitude of 6.8 struck Olympia and the greater Puget Sound on Feb. 28, 2001, a good portion of the city quickly became a construction site.

Today, the scarred and collapsed roadway along Deschutes Parkway is the only remaining evidence of the earthquake that rocked the city a little over a year ago.

The quake tore up much of the 1.6-mile roadway that had been constructed over fill material, which rests atop various layers of soil. From top to bottom, the layers include 17 feet of mixed fill, 10 feet of water-soaked sand, eight feet of peat and 35 feet of unstable sand, which is constantly in contact with groundwater under pressure. The earthquake's motion caused the various layers of soil to mix together, making the road buckle, separate and drop.

Unfortunately, this was not the first earthquake damage to occur here. This same area sustained damages during a 1965 earthquake and more recently in 1996, when a landslide broke two main sewer lines that carry wastewater for the town of Tumwater to a treatment plant in downtown Olympia.

To correct the problems, the Washington Department of Transportation awarded a contract to the Sumner, WA-based RCI Construction Group. The contract called for completely rebuilding the concrete roadway that had been closed following the quake and to carry out several storm water and wastewater installations.

Washington State DOT Project Engineer Troy Cowan said RCI was responsible for virtually all of the pipe work on the project. "This included a new 1.6 mile storm water system which runs the entire length of Deschutes Parkway."

According to Cowan, the system is basically made up of corrugated polyethylene pipe and ductile iron pipe, most of which is 12 inches in diameter and installed through open cut. The installed system will collect and treat storm water runoff for quality with multiple Stormceptors before it is released into nearby Capital Lake.

RCI's contract also covered the open cut construction of 6,781 feet of parallel 20- and 22-inch HDPE to complete a sewer force main that runs from Interstate 5 to the LOTT pump station on the west side of Deschutes Parkway.

In addition, RCI's contract also covers the installation of 10 culverts at the north end of the project to convey runoff from the hillside and to drain the toe of the hill out to the lake.

As noted by Cowan, several things make the culvert installations somewhat different. First, the lake level had to be lowered four feet to facilitate the installation. Also, because of the likelihood of a future earthquake, the DOT elected to use 1,992 feet of 20 and 26-inch HDPE in the culvert construction.

Commenting on the selection of HDPE for the project, Zack Smith of Maskell-Robbins (MR), Mountainlake, WA, a distributor and fittings fabricator of HDPE pipe as well as one of the largest distributor of McElroy fusion equipment in the United States, said Olympia needed a pipe that could withstand the unstable ground conditions anticipated in this area.

Smith noted that since the area is at sea level and groundwater is always in constant contact with the pipe, it is essential that the pipe doesn't leak.

"The toughness of HDPE and its ability to withstand tremendous force has been proven by its surviving major earthquakes such as those that occurred in Kobe, Japan in 1995," Smith said.

HDPE is currently used in 90 percent of all gas distribution pipelines and is rapidly gaining acceptance in water and wastewater applications worldwide. Japan is also installing HDPE for the majority of its water infrastructure and HDPE plays a prominent role in water distribution in the United Kingdom as well. In 2000, an analysis carried out by Corporate Development Consultants (CDC) on the type of pipe installed by water companies in the UK, France, Italy, Spain and Germany indicated that the majority of the pipe installed below 12 inches in diameter is HDPE.

Moreover, HDPE usage in European water distribution systems is more for water conservation than tough soil conditions. Recent studies by the University of East London confirm that PVC and iron pipe failures are common. Another study by the United Nations Economic Commission for Europe estimates the cost of leaks in terms of potable water alone for the entire region at approximately $10 billion a year

With growing concerns of water shortages in many parts of the U.S., utilities, regulatory agencies, and conservationists are reviewing distribution systems and evaluating leaks. They're finding that future repair costs will be staggering.

"We're seeing HDPE being used in the Northwestern states mainly because of the tough soil conditions," said Smith. "At other locations it is being implemented as a water conservation tool because of its leak-proof qualities."

According to a recent Community Water System Survey, water utilities self reported that leak rates averaged 13 percent. Many in the industry feel this number is wildly optimistic, and say 20 or 40 percent is likely the norm.

Figures from yet another study by the International Water Supply Association show 20 to 30percent of the water that has been purified for human consumption never reaches its intended destination. This, coupled with the ongoing expense of patching old and failing infrastructure is making it tough for water companies to operate economically.

"When replacing or rehabilitating forced water mains, municipalities strongly stipulate that they not leak," said Gerry Baker, a project manager and estimator with RCI. "The fact that this project is in an active fault zone and in liquefied soils, makes it even more crucial that the pipe not come apart at the joint."

He noted that the main reason HDPE doesn't leak at the joint is the manner in which the pipe is joined. "The pipe is heat fused together and actually has no joint. The joint is the primary point for leaks in most pipeline system."

Unlike steel and iron pipe, which is damaged by corrosion, HDPE is corrosion resistant. "On this particular project," he said, "the wastewater pipeline is being fused together with McElroy TracStar 500 and TracStar 900 fusion machines."

The TracStar 500 is a self-contained, self-propelled, all-terrain hydraulic fusion machine that will butt fuse all pipe sizes from 6-inch IPS to 18-inch DIPS.(180 mm - 500 mm) The Coach fusion control system controls the hydraulics, heater temperature, and allows for on-machine operation or remote operation. The system is programmable for multiple pressure set points and performs pressure calculations, with drag compensation and more. An integral data-logging feature is standard, and automatic fusion is available as an optional feature. The machine also incorporates McElroy's patented Centerline Guidance System. It fits in a standard long box truck bed for easy transport. The carriage may be easily removed for in-ditch use. Power is provided by a liquid cooled diesel engine.

The TracStar 900 is a self-contained, self-propelled, all-terrain hydraulic fusion machine to butt fuse pipe 12-inch IPS to 36-inch OD. It too is equipped with Coach fusion control system controls the hydraulics, heater temperature, and allows for remote operation. The system is programmable for fusion pressure, drag compensation and more. The rubber-tracked unit is powered by a liquid cooled diesel engine. A wireless remote provides full control of the TracStar 900 for precision placement, and optimum visibility on the job site.

The toughness of HDPE and its ability to withstand tremendous force has been proven by its surviving major earthquakes

Zack Smith

Over the course of the project, the two machines will be used to fuse three different sizes of pipe at several locations. Because of the various work locations, several different staging areas were required for the mobile fusion equipment to be able to track back and forth between these locations without the use of heavy transportation equipment.

"Many times over the course of a job a fusion machine and its generator have to be loaded, transported a short distance and then unloaded," Smith said. "This can take a lot of time and require at least three employees to operate the equipment needed to make the respective moves.

A big advantage of the TracStar machine is the savings realized in transport time. The fusion operator can simply drive the TracStar to the next fusion staging area."

Another benefit of the TracStar is its off-carriage capabilities.

"For crews installing the culverts, the lake surrounding the area had to be drained about four feet to provide access where the work was to take place," he explained. "This allowed the carriage of the fusion machine to be removed and lowered into the culvert and the HDPE fused in the ditch."

At the same time, the city was able to take advantage of the lower water level to rid the lake of Eurasian milfoil - a rapidly growing plant that depletes oxygen from the water and is detrimental to the fish population.

Auger Bores

Two auger bores were carried on the project by Northwest Boring of Woodenville, WA, to allow pipe work being installed to pass under existing railroad tracks. At these locations, Cowan said crews would install a single 54-inch diameter steel casing to house the two HDPE pipelines.

For Northwest Boring, unexpected challenges began cropping up almost as soon as the work began. When the railroad was constructed in the early 1900s the difficult soil conditions were taken into consideration and pilings were driven into the ground to support the tracks. Northwest Boring was unaware of the obstructions until they began the bores.

"We had to do a lot of chainsaw work to remove the old piling logs but we were ultimately able to complete all the bores on time," said Don Gonzales, president of Northwest Boring.

As to the project's completion, DOT's Cowan said that while the project was not due to be completed until December 20, crews are currently running ahead of schedule.

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