Engineering Inc. - Spring 2020 - 37

MULTI PROJECT

SAN ANDREAS PIPELINE
PROJECT: SAN FRANCISCO PUBLIC UTILITIES COMMISSION'S SAN ANDREAS PIPELINE NO. 2 SAN BRUNO, CALIFORNIA
FIRM: TOWILL, INC. CONCORD, CALIFORNIA
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he San Francisco Public Utilities
Commission (SFPUC) wanted
to improve its vast water infrastructure to protect against future
earthquake damage. One of the projects
involved replacing three sections of
pipeline totaling 1,800 feet of the San
Andreas Pipeline No. 2, built in 1929 as
part of the Hetch Hetchy regional drinking water system that supplies water to
1.8 million residents and businesses in
the Bay Area.
Instead of digging up and replacing
the buried pipeline, SFPUC decided
to incorporate a sliplining method,
which involved inserting a new 48-inch
diameter pipe into the existing 54-inch
pipe. Sliplining would not only save time
and money but also avoid road closures
and environmental impacts during the
project.
However, SFPUC's original drawings
and other information for the nearly

TOWILL, INC.

Towill field staff access
a pipeline at one of
three project locations.

100-year-old pipeline were outdated and
incomplete. So the project's design firm,
Kennedy/Jenks Consultants, contracted
Towill, Inc., to collect and analyze new
information using integrated surveying and static terrestrial laser scanning
(STLS) technologies.
"Determining the exact size of the
pipe was definitely a
challenge we faced," says
Frank Borges, principal at
Towill.
The traditional
measurement process is to
assemble a simple wooden
cross to the replacement
pipe's diameter and simply
walk it down the middle
of the existing pipe to
determine if the new one
will fit. But with such
FRANK BORGES
an old pipeline and antiPrincipal
quated schematics, it was
Towill, Inc.

feared the cross technique might miss vital
details and not be accurate.
"Our project manager, John T. May,
came up with the solution of scanning the
inside of the pipe to get highly precise information," Borges says.
This entailed in some places cutting
access holes on top of the pipe, lowering
a person inside with their
equipment and making
scans in 10-foot increments.
Although the Towill team
was familiar with the necessary technologies, "I would
classify this as a dynamic
project," Borges says. "We
needed to maintain accurate
data, so we needed a flexible
plan for when unexpected
things came up."
Towill actually tested the
idea in its offices, simulating scanning methods and
targets along a corridor
between cubicles that had the same width as
the replacement pipe.
However, once inside the existing pipe
itself, employees discovered that the interior
was even narrower than predicted, since it
was lined with 2 inches of calcite that was
not shown on any plan set. Furthermore,
instead of using magnets to affix the STLS
control targets to the interior walls of the
pipe, as originally planned, they came up
with an alternate solution: to affix steel
washers with high-grade marine epoxy.
Based on the survey information, a final
recommendation was made for a 42-inch
replacement pipe.
The four surveyors chosen for the fieldwork underwent extensive safety training
to qualify for access to the confined spaces.
They finished the project in eight days,
two fewer than planned, and ultimately
provided the client with survey data allowing it to begin the sliplining project.
"Our work was performed safely, on
time, within budget, without incident,
and to the client and owner's satisfaction,"
Borges says.
SPRING 2020 ENGINEERING INC.

Engineering Inc. - Spring 2020

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