Introduction
The high pace of sanitary sewer construction in
the Las Vegas area is still on-going with seemingly no end in
sight and HOBAS centrifugal cast fiberglass reinforced polymer
mortar (CCFRPM) pipes continue to play a significant role. The
recently completed City project, the Sandhill Relief Sewer,
utilized over 18,000 feet of mostly 54" and 66" HOBAS
pipes installed primarily by open cut methods. The job also
included several elbows, a lateral wye and 30 tee base manholes
(90% with flanged top risers).
Limited
Specification
Since over two-thirds of the pipes are buried
in the Las Vegas Wash, design engineer Black & Veatch of Las
Vegas, specified a slurry pipe zone backfill surround to prevent
flotation in shallow areas and to protect the pipes from potential
erosion. Additionally, as on all recent City jobs to assure the
design life is achieved, only corrosion resistant or corrosion
protected pipes were allowed. Further, to minimize infiltration, a
low leakage allowance was also included. Finally, with some
alignments in streets, cuts up to 25 feet, and the demanding wash
conditions, coupled with all of the other needs, the pipe
specifications included only RCP with 360 degree PVC T-lock lining
and CCFRPM.
Lowest
Installed Cost
Although the CCFRPM pipes were priced
competitively, it was the lower installed cost that led first time
installer, Tab Construction of North Las Vegas, to choose HOBAS.
Of greatest significance to Tab was the pipes’ longer lengths
and lighter weight, which decreased laying costs, particularly in
these large diameters. Additionally, fast and easy field length
adjustments, needed for make-up pieces, generated additional
savings.
Installation
Ease
Tab developed a low moisture, lean slurry mix
with pea gravel and fly ash ingredients that flowed well but
exerted so little uplift on the pipes, that anchoring was not
needed during placement to prevent flotation. This, combined with
the push-together, gasket-sealed joints fast assembly, allowed
routine daily production rates of a few hundred feet. Tab
experienced more benefits by direct jacking about 1300 feet of the
CCFRPM pipes, which eliminated the casings specified at four major
road crossings.
High Performance
The installed pipes have little deflection (ovaling)
with none observed over 1%. The entire 3.5 miles of HOBAS
line, including the tee base manhole connections, not only met the
leakage requirements, but passed the infiltration test without any
leaks! These outstanding achievements are a repeat performance for
HOBAS CCFRPM pipes, not only in the Las Vegas area, but across the
USA.
Preferred
Material
Tab crews enjoyed great success installing
HOBAS pipes and preferred the CCFRPM product over the RCP used on
another segment of the Sandhill project. In fact, Tab has already
committed to purchase 6000 feet of 36" HOBAS pipes (half open
cut installation and half direct jacked) for another Las Vegas
area job (our ninth) for the Clark County Sanitation District
which will commence in August. The continued success of HOBAS
pipes in Las Vegas shows they are the winning ticket.
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