Introduction
Significant portions of the new Brushy Creek
Regional Wastewater System interceptor line that will eventually
extend from the Cedar Park WWTP through Round Rock (TX) to the
Brushy Creek Regional WWTP (approximately 15 miles) are being
constructed with HOBAS centrifugal cast fiberglass reinforced
polymer mortar (CCFRPM) pipes. A recently completed section,
contract 6, supplied by HOBAS, was an all fiberglass system
consisting of over 7000 feet of 72" installed by open cut,
160 feet of jacked 72" and twenty-two 72" x 36" tee
base manholes.
Multiple
Design Criteria
Several important performance criteria guided
the pipe specifications developed by PBS & J of Austin. Early
initial flows and long retention times made corrosion resistance
to septic conditions critical to assure a long life. Low or no
leakage was paramount due to the burial alignment immediately
adjacent to Brushy Creek. With cover depths up to 25 feet (open
cut) and 37 feet (jacked at a railroad crossing), reliable
structural performance was a must. Because of these needs, a 50
inch-gallon leakage limit was established and only two pipes were
specified; RCP with PVC T-lock lining or CCFRPM.
Most Cost
Effective
Low bidder, Garney Construction Co. of Kansas
City, evaluated HOBAS pipes as most cost effective even though the
delivered pipe price was not the lowest. Several installation
advantages contributed to the estimated field savings. It was
judged that the longer (20 feet), lighter (300 lbs./ ft.) pipes
could be handled easier and installed faster especially in the
deep cuts and in the wet conditions expected due to a high water
table. Fewer joints also meant less chance of leakage. Additional
savings accrued because of the narrower excavation required for
the smaller OD (75" versus 86"). For these reasons and
more, HOBAS pipes were selected.
Tough,
Fast & Tight
As expected, handling of these large pipes was
easy, although Garney was most pleased with the pipes’
durability and toughness. Burial was quick using the dumped
crushed rock pipe zone surround and the resulting deflection
performance was exceptional with a maximum 1.5% measured, although
most were well below 1%. The push-together, gasket-sealed coupling
joints assembled fast and passed all air tests with no leakage at
all! Further, since these couplings seal on the unaltered, natural
pipe OD surface, the field length adjustments required for precise
placement of the tee base manholes were a breeze for the Garney
crew.
Best Pipe
The final walk through with the dewatering
system removed, resulted in an impromptu infiltration test which
revealed a completely tight, dry line including the all
fiberglass, gasket-sealed manholes. With so many benefits and a
trouble-free job, it’s no wonder Garney personnel labeled HOBAS,
"the best pipe". HOBAS pipes are currently being
installed on another segment of the Brushy Creek system and are
specified for upcoming contracts.
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