|
|
|
|
|
|
|
|
|
 San
Francisco Sewer Collapse On December 11, 1995, winter
rains and construction activities combined to cause the failure
of a century-old six-foot brick sewer underlying the prestigious
Sea Cliff area of San Francisco. The sudden and massive torrent
released from the sewer scoured the dune sand hillside and
eventually undermined homes and roads. One house was completely
destroyed when it fell into the pit created by the erosion.
Exponent's Geo3 staff assisted the City's Department of Public
Works by performing an independent investigation of the failure.
We determined that the sewer had been pressurized by a new
hydraulic structure downstream of the failure site. Additionally,
vital ground support around the sewer had been reduced by
a sinkhole that developed adjacent to the sewer caused by
excavation of a tunnel beneath the sewer. The findings of
the investigation were presented in a widely distributed report
and at several public meetings.
|
 Drillpipe
Failure Assessment In many locations around the world, the
extraction of oil, gas, and water may cause the earth's surface
to subside. Such ground subsidence can lead to damage or failure
of surface structures, such as offshore platforms, and damage
of the well piping systems, which can result in premature abandonment
of expensive production wells. In one case, our client sought
the expertise of Exponent geomechanical engineers to determine
why such oil well drillpipe failures had occurred and sought
guidance in how to prevent such failures in the future. The
figure shows the results of a computer model of 18 years of
simulated production from an oil field in southern California
and represents a slice of the earth's crust (blue) with changes
in oil pressure during production shown by other colors. As
a result of the long-term petroleum production, the earth's
crust has deformed, leading to ground subsidence, which caused
severe damage of the steel well pipe shown in the enlargement.
|
|
 Landslide
Analysis In late December 1996 and early January 1997,
a series of storms originating in the central Pacific Ocean
dropped heavy, prolonged, and unusually warm precipitation
across northern California. The warm precipitation at high
elevations and an above-normal snowpack combined to create
widespread snowmelt. The resulting floods produced the largest
recorded peak levels and discharges of numerous streams and
rivers in the gage's operational history and produced widespread
property damage across northern California. Exponent's geotechnical
and structural engineers worked with insurance companies to
determine the cause and origin of numerous bridge failures
and landslides, such as that shown in the adjacent photo,
along the South Fork of the American River.
top | back
| next
|
|
|
