EARTHQUAKE ENGINEERING

Stafford Dam Outlet Structure
Location: Novato, California

The outlet tower was built with the Stafford Dam (originally the Novato Creek Dam) in 1951. The Stafford Lake is the potable water storage reservoir and the outlet tower discharges water to the NMWD downstream water treatment plant that is undergoing expansion and treatment upgrades. In 1984, a new caisson box was installed over the inlet of the bottom 30-inch scour gate to keep the gate free from the rising level of mud at the bottom of the dam. In 1999, during a test of the 30-inch gate, it was discovered that the operating stem had become bent, the lower stem guides had broken away from the tower, and the valve slide brackets had broken off the scour gate assembly. A diving team was brought in to physically move the gate into the closed position and it has been closed ever since.

The State Division of Safety of Dams notified the NMWD that the scour gate must be made operational to comply with operating requirements for flood control.

The C+D project included a condition survey (underwater diving), structural and mechanical assessment of the current condition of the outlet structure, recommend replacement, rehabilitation and strengthening alternatives for the outlet structure service and scour gates and other modifications to renovate the outlet tower for another 50 years of operation.

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Vine Street Water Treatment Plant
Location: Albany, Oregon

The City of Albany has had two seismic vulnerability assessments performed on buildings and structures at the Vine Street Water Treatment Plant (WTP). The seismic risk assessment identified building structure and equipment deficiencies that are life safety hazards and pose a risk of disruption to water treatment, pumping and storage following a major earthquake.

Creegan + D’Angelo designed seismic retrofits for plant buildings, equipment, and the steel tank reservoir that reduced the life safety hazard and decreased the potential plant off-line period following a major earthquake.

The project included coordinating the applications for performing work on historic structures through the state historic structures office, and the City of Albany’s historic district commission.

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East Bay Municipal Utility District - Water Storage Tanks
Location: California East Bay

EBMUD selected C+D Structural Engineers for the Seismic Improvement Program due to our strong background in earthquake engineering. The services we provided under this contract include:

  • Seismic assessment of water storage tanks
  • Preparation of construction plans and specifications for strengthening
  • Construction inspection
  • Strengthening includes foundation piers, tank anchor, additional circumferential prestressing, and mechanical and electrical improvements.

Two contracts in 2000 and 2001 have included nine tank retrofits. We also developed an advanced non-linear computer modeling and analysis tool as a special project to allow evaluation of complex geometry and partially buried tanks.

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East Bay Discharge Authority
Location: San Lorenzo, California

The East Bay Discharge Authority provides the wastewater collection, pumping, and outfall discharge for four East Bay Water Pollution Control Plants. The plants include the Union Sanitary District, City of Hayward Wastewater Treatment Plant, City of San Leandro Pollution Control Plant, Ora Loma Wastewater Treatment Plant, and the Marina Dechlorination Facility. These four facilities have a capacity to treat and discharge up to 200 MGD. The post earthquake performance of this facility is critical to protect the health of the customers and the aquatic life in San Francisco Bay.

EBDA selected C+D to provide earthquake vulnerability reduction and construction retrofit documents to "maintain operations" after a major earthquake. Our services included Building, Structures and Utility Vulnerability for earthquake forces and geotechnical hazards.

The work we provided includes:

  • Upgrade the facilities to meet seismic performance goals
  • Minimize impact to operations during construction
  • Soil hazard from liquefaction, differential soil movement, and lateral spreading
  • Related hazard to pipe breaks and pipe utility connections to structures
  • Emergency response plan to provide temporary power, pumping and piping to pump wastewater around pipe breaks before repair
  • Outfall pipe vulnerability assessment
  • Recommend retrofits for improved seismic performance
  • Cost estimates of retrofit construction
  • Permit approval, bidding and construction administration and inspection

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Water Pollution Control Plant
Location: San Leandro, California

The Water Pollution Control Plant at San Leandro is a lifeline facility situated only two miles from the Hayward Fault, and is required to maintain operations following a maximum credible earthquake, as well as to protect life safety, health, and the environment. Certain structures and equipment in the plant are essential to maintain treatment and disinfection of the sewage flow and to avoid a public health hazard or pollution of San Francisco Bay.

C+D developed seismic performance criteria for the essential and nonessential components of the facility, based on operational priorities; which include:

  • Prevent release of chlorine gas or other hazardous materials
  • Prevent fire or explosion of methane or other substances
  • Prevent life-threatening collapse or falling hazards
  • Maintain the design sewage flow through the plant and pump stations
  • Disinfection and primary treatment to protect the public health
  • Secondary treatment to protect the environment
  • Harden control equipment, communications, power generation, and other emergency support facilities.
  • Protection of public property.

The essential components are "hardened" to prevent failure and maintain critical sewage treatment operations after a magnitude 7.3 earthquake on the Hayward Fault. System redundancies are incorporated to ensure high operational reliability of the plant.

Work included site engineering, drainage plans, utility service plan and exterior lighting and specifications. Work involved coordination and approvals through local and state authorities for development within the Lake Tahoe Basin.

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