Underground Construction - November 2018 - 29

tion would inconvenience Houston's customers and potentially disrupt their water supply.
Given the limited time available and the critical
nature of the C-System, the project team determined that these options were not feasible.
Consequently, the project team decided to go
with option three.

Low lift pump station direct
connection
At the time of the C-System leak, the Low Lift
Pump Station Direct Connection project at
the East Water Purification Plant was nearing
completion. The project consists of 36-, 42-,
48-, 54-, 60- and 84-inch sections of water line
for transporting raw water from CWA's B and
C lines to the low lift pump stations at plants
1, 2 and 3 at the East Water Purification Plant.
The project, which was completed in September
2018, allows the city to obtain raw water from
a single source without having to pump into
the forebay for plants 1 and 2, and provides
redundancy to use either the B or C system at
all three plants.
"At the time of the leak, more than 90 percent of the pipe had been constructed and only
the control valves and electrical work needed to
be installed," said Mack. "CWA and the city decided to use temporary spools of pipe to fill the
gaps and back-feed the water."
Subsequently, LAN performed hydraulic
modeling to identify if the B-System water
line, the Houston 60-inch raw water line and
Low Lift Pump Station Direct Connection were
capable of back-feeding up to 100 MGD of raw
water to plant 3. The analysis utilized a newly
built hydraulic model of CWA's B-system in
Bentley's WaterGEMS, built in 2017 for its
condition assessment program. Model updates
were made for inclusion of system water mains,
valves and system service line demands. Updated GIS files provided a geospatially correct
model. Following the hydraulic modeling, the
project team determined that this option could
provide the 100 MGD of water the city needed
(Figure 2).

15 internal joint seals (WEKO-SEALS) from
Miller Pipeline (the leak on the 102-inch line
was assumed to be located at a joint within
the pipeline). The 15 seals spanned the area
of joints suspected to be leaking. Structural Technologies was put on notice to provide
budgetary pricing for carbon fiber reinforced
pipe rehabilitation and to complete as-needed
and/or emergency repairs. CWA also lined up
welders from the original pipe manufacturer
(Gifford-Hill-American, now Thompson Pipe),
if a welded repair was needed.
After detailed preparation, the C-System
was isolated on Feb. 23 and dewatering was
started by CWA crews later that night. Two
days later, CWA staff and LAN engineers carried out a manned entry to identify the source
of the leak and observe any other distress.
Observations included identifying unusual
circumferential and longitudinal cracks, disbonding of the concrete core, deficiencies in
the manually applied joint grout, and other
similar issues.

The results of the visual observations
included:
* 177 pipe sections were visually inspected/observed (approximately 2,732 linear
feet/0.52 miles).
* Installation of the pipe sections generally
followed the manufacturer's lay schedule.
* Interior joints overall reflected evidence of a
good-quality, well-mixed grout application.
Of the joints inspected, less than 5 percent
had minor deficiencies.
* One welded joint (closure piece) was actively
leaking, and one joint was suspected to be
leaking.
* An abandoned air tap was found with evidence of severe corrosion.
* None of the pipes exhibited visible cracks,
spalling or delamination of the inner concrete core.
One joint, more specifically a closure piece,
was observed to be actively leaking. Because
joint grout was intact, LAN was unable to
identify the exact cause of the leak. The closure

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Pipeline shutdown and repair
As the project team was working on the direct
connection, CWA and LAN contacted pipe repair subcontractors to have contracts in place
and materials and crews on stand-by in preparation for shutdown and manned entry.
During the planning phase, CWA procured

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Underground Construction - November 2018

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