Seismic-Prone Project Area Requires HDPE

September 2008 Vol. 63 No. 9

A new retail power center in Burnaby, British Columbia, Canada, is quite literally ‘floating’ on a bed of wood, gravel and concrete. In an area where construction must always consider the impact of seismic activity, the potentially fluid nature of this site’s foundation meant that for underground contractor TAG Construction Ltd. of Langley, British Columbia, the choice when it came to the construction of the underground water and sewer lines was crystal clear.

“In this case it was readily apparent that only HDPE pipe would be able to sustain the flexible nature of the site,” said professional engineer Michael Grant of TAG.

The site of the 302,000 square foot Big Bend Crossing shopping center had been a waste dump for building demolition material for many years. Then it was pre-loaded for construction using building excavation material from sites throughout the lower mainland.

“This made for very fluid soil conditions,” explained Grant. “The design using HDPE mains and services for water and sanitary was based on the ‘flexible’ nature of the site, given the presence of the wood wastes below and their ground water content, and the need to ensure the integrity of the pipe in the moving ground.”

HDPE pipe can be bent to a radius 25 times the nominal pipe diameter for mid range pressure pipe, 20 times for heavy wall pipe and 30 times for low pressure pipe. In addition to eliminating many fittings required for directional changes in a piping system, the “flex” factor makes HDPE pipe ideal in areas of high seismic activity.

An advantage of PE pipe is that gaskets or external joints are not required, explained Brad Warning of Prolite Systems in Maple Ridge, British Columbia, the specialists who provided the pipe, fittings and fusion expertise for the Big Bend Crossing project. PE pipe is joined using a heat fuse process with machines such as the Connectra Fusion 14 inch hand pump machine utilized on this project. The fusion process creates an area at the joint that is even stronger than any other point along the length of pipe, and is therefore equally resilient when bent.

Earthquake considerations

In America, municipalities and states in quake prone regions such as southern California have been installing PE pipe at increasing rates. A report on damage rates to gas distribution lines following the Northridge, CA, earthquake in 1994, stated that while PE makes up 41 percent of the gas piping system in the area, only 27 of the 709 leaks (or 3.8 percent) occurred in PE pipes.