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HOBAS centrifugally
cast fiberglass reinforced polymer mortar pipe was the product of
choice for the City of Houston for the sliplining rehabilitation
of the 84" Lockwood Sewer – Segment 2, located near
downtown Houston. Approximately 6,000 feet of 72" SN 46 HOBAS
fiberglass pipes were used to reline the existing 84" MRC
(monolithic reinforced concrete) sewer line, which was severely
corroded due to sulfide attack. Although the installer, BRH Garver
of Houston, has had numerous successful jacking and tunneling
experiences using HOBAS pipe, this was their first sliplining
project utilizing HOBAS pipe.
Easy Execution
The Lockwood project was divided into two
contracts. Jalco, Inc. of Houston, Texas lined Section 1, also
using HOBAS pipe. The slipline installation for Section 2 began at
a bulkhead installed on Segment 1. By-pass pumping was not allowed
but the flow could be diverted, using sandbags, upstream from the
construction location. HOBAS pipe’s lightweight wall and smooth
constant O.D., enables lower insertion forces so the pipes were
easily pushed, one at a time, using a Bobcat Skid Steer Loader.
Fast and easy assembly was common with the push-together,
gasket-sealed, low-profile bell & spigot joints. The maximum
daily productivity rate was reported to be approximately 275
ft/day. Once the entire pipe system was relined the annular space
was grouted. Grout ports were not allowed on the project, so the
line was grouted from manhole to manhole through bulkheads at the
ends. To prevent floatation and eliminate blocking, the pipe was
filled with sewage to 3/4 depth.
Difficult Decisions
The challenges on the project included 8
curves, numerous irregularities in the line, and several field
changes. It was decided that the ± 45-degree curves were to be
constructed using 72" mitered elbows and installed using
direct-bury methods. Numerous irregularities were encountered and
easily relined using 5 ft and 10 ft pieces of HOBAS pipe. To
minimize construction cost and surface disruption, smaller
circular access shafts were constructed which required manhole
tee-bases with leg lengths shorter than possible to fabricate and
assemble. This late modification was accommodated by field
fabrication of the fiberglass manhole tee-bases, a new procedure
for Houston. The versatility to field fabricate the HOBAS manhole
tee-bases translated to savings of time and money, and also
resulted in precise placements of the manhole systems.
Slipline Success
The numerous challenges encountered were easily
overcome due to creative solutions and skilled execution by the
contractor, BRH Garver, the willingness of the City of Houston to
allow new methods, and the versatility and dependability of HOBAS
fiberglass reinforced pipes. Not only was the project successful
but it was completed ahead of schedule.
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