The Water Department at San Francisco Water Pow- er Sewer (SFWPS) provides water services to the 2. 6 million residents of the greater Bay Area, and
manages retail drinking water for San Francisco and wholesale water for three Bay Area counties.
Underground digging on subway tunnels triggered a large
sinkhole in the South of Market neighborhood of San Francisco, a very densely populated area with heavy traffic. The sinkhole measured 50 feet wide, 75 feet long and 40 feet deep.
The resulting falling debris damaged the cast iron pipe that
had been originally installed almost a hundred years ago. The
pipe was left exposed with utility lines channeled alongside the
piping left unsupported, further putting pressure on the pipe.
The piping needed to be quickly repaired to restore water
service so that street-level traffic could resume. The piping
ran between a number of concrete utility vaults and had a
pressure rating of 300 psi. A coupling was required that could
safely handle the high water pressure so that entire lengths
of piping between the vaults would not have to be replaced.
Such an operation would have required connecting the pipes
with lead joints, a very time-consuming and labor-intensive
process. With more piping to replace, the labor and material
costs would be enormously higher compared to repairs where
only sections of pipe needed to be replaced.
Richard Gonzales is the superintendent of construction,
maintenance and operations for SFWPS and oversees the
Water Department and High Pressure Fire System for the
city’s public utilities commission. He and his team of engineers
decided that using the 12” HYMAX coupling would make the
repair faster to help return the street to its usual state while
The pressure rating for the HYMAX coupling was 350 psi,
which was more than enough to maintain the integrity of the
pipe. Instead of having to remove and replace six lengths of
cast iron pipe, Gonzales’s crew was able to simply replace only
BY ED NUNES
Falling debris from the sinkhole damaged the cast iron pipe that had
been originally installed almost a hundred years ago.
Instead of having to remove and replace six lengths of cast iron pipe,
Gonzales’s crew was able to replace only damaged sections with new
sections of pipe connected on either side with HYMAX couplings.