Underground Infrastructure - July 2023 - 26

Rehab Technology
With a history of blockages and collapses,
TRA was set to award a contract for
fi nal design to replace and rehabilitate this
segment of the pipeline when the SSO occurred.
TRA staff mobilized immediately
and worked expediently and progressively
to determine if this was another blockage
or more signifi cant pipe break.
Th is segment of the system is located
in a channel with 25-foot tall sidewalls
which hindered equipment access. In order
to isolate the line for investigation, the
contractor not only set up a traditional bypass
for the line, but also sent equipment
into the drainage channel to build earthen
berms to contain the wastewater overfl ow
within the work area. Two trailer mounted
pumps were used to pump the water
contained between the berms located at
manhole 210WC and downstream at 180
WC out of the drainage channel and into
manhole 180WC to prevent downstream
contamination, as depicted in FIGURE 2.
Preliminary examination confi rmed
the blockage was located somewhere
between manhole locations 200WC and
190WC. At manhole180WC, cleaning
trucks were stationed over the downstream
manhole. Unfortunately, the torrential
rains saturated the earth around
FIGURE 2: SSO location and project limits
manhole 180WC, limiting truck access
and causing setup to take hours rather
than minutes. A separate cleaning vehicle
was stationed over manhole 190WC
and att empted to clear debris from the
pipe between 190WC and 200WC.
Several passes of jett ing were att empted
to dislodge the obstruction were unsuccessful,
but they verifi ed the presence of
a large blockage fi ve to 10 feet upstream
of manhole 190WC. Th e apparent challenge
was to clear a blockage located
under the reinforced concrete apron of
the drainage channel, approximately 25feet
deep and adjacent to a residential
home. It was discovered that continued
corrosion of the 27-inch RCP had leſt no
remaining pipe across the channel fl oor
and, due to the blockage, it was unclear
how much pipe wall remained under the
channel sidewall.
HDD cleanout
FIGURE 3: What we couldn't see - Large void under the embankment and driveway
FIGURE 4: Replacement and backfill of 190WC
26 JULY 2023 | UndergroundInfrastructure.com
A horizontal directional drilling rig was
brought in to clean out the debris from
inside the collapsed pipeline in order
to minimize deep excavation near the
residence. Th e purpose was to place
a steel encasement pipe beneath the
drainage channel wall up to manhole
190WC reestablishing a clear passage
up to the exterior of the manhole. Aſt er
the encasement pipe was installed, a new
carrier pipe would be inserted within to
transport the wastewater.
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Underground Infrastructure - July 2023

Table of Contents for the Digital Edition of Underground Infrastructure - July 2023

Underground Infrastructure - July 2023 - 1
Underground Infrastructure - July 2023 - 2
Underground Infrastructure - July 2023 - 3
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