Underground Infrastructure - October 2023 - 23

A 96-inch diameter Earth Pressure Balance Machine
(EPBM) was delivered on site at the location of the
41-foot diameter secant pile launch shaft.
a major step in achieving the city's increased
resiliency goals to improve redundancy
and reliability within its water
transmission system.
2020, the percentage has dropped to
21 percent, and a 9-percent decrease in
ground water pumping from 2019.
The SWTP 72-inch Water Line from
Emancipation to Tuam is the first segment
in a series of four that will serve
as a refill line to the Southwest Pump
Station (SWPS). After rupture of a 42inch
surface water refill line in 2004, the
city evaluated vulnerability of supply to
its three major repump stations.
SWPS is the heart of the system, and
shutdown of the more than 50-year-old,
66-inch, pre-stressed concrete cylinder
pipe (PCCP) - the current primary
source - would impact the system's ability
to supply the western half of the city.
A new 72-inch water line was initially
identified as a secondary refill line but
would become the primary supply line
for SWPS and provide an opportunity
to assess and rehabilitate the existing
66-inch water line.
Preparing for the future
After a decade of astounding 21.6-percent
population growth, the Houston
region is expected to double its current
population by 2050. This project was
In this densely urban part of Houston,
with an average of over 170,000 vehicles
per day recorded along this section
of US-59, the 96-inch-diameter tunnel
crossing under US-59 was considered a
record-breaking tunnel installation. The
874-foot-long tunnel required shafts to
be constructed to a 79-foot depth, which
was 33 feet below sea level. For a tunnel
of this scale, challenges of equal magnitude
were faced throughout the design
and construction process.
The project began at the intersection
of Emancipation at Polk St. in
East Downtown, and ended at the intersection
of Tuam and Crawford, in
Midtown. With a total of over 7,800
linear feet, the scope of work included
a 72-inch water transmission line, full
roadway reconstruction, major drainage
improvements, traffic signalization
improvements, street lighting improvements
and sidewalk improvements.
Because of the TxDOT future freeway
expansion, with a proposed depressed
section and future drilled shaft retaining
walls, the tunnel was designed at a depth
to avoid future freeway improvements.
The length of the tunnel was also designed
so that the completed length would clear
the future expanded freeway width.
Part of the planning and design included
thorough geotechnical exploration,
which identified various soil conditions
including fat clay, lean clay, sand
with silt, sandy, silty clay and silty sand.
A zone of hydraulically charged silty
sands, also known as running sands, was
discovered. With any type of trenchless
application, there is a high risk of soil
unraveling and difficulty controlling the
groundwater in this type of soil.
While the tunnel invert depth was
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Underground Infrastructure - October 2023

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