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Engineers Lay Blame on Oroville Management

Thursday, August 3, 2017

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A recently issued report from a group of engineers takes a scathing view on the root causes of this year’s concrete problem at California’s Oroville Dam, asserting that the structure was “managed to failure” and “regulated to failure.”

Robert Bea, professor emeritus of engineering, and Tony Johnson, of the Center for Catastrophic Risk Management, both from the University of California-Berkeley, headed the team of Berkeley engineers who carried out the analysis, published July 20. The group’s conclusions are that the defects in the dam’s main spillway were “highly interactive and cumulative,” stemming from ineffective guidelines and procedures on the part of the California Department of Water Resources, which oversees the structure.

Images from Bea/Johnson report

Report co-author Robert Bea raised concerns about patches of green vegetation on the abutments, which he believes indicate water seepage.

The dam—the tallest in the United States—became the focus of concern in February, when a massive area of its main concrete spillway crumbled. When the DWR attempted to switch overflow releases to the unpaved auxiliary spillway, which had never been used in the dam’s nearly 50-year history, that spillway eroded to the point where officials became concerned the concrete weir might fail.

The February crisis, which came in the midst of heavy rains in the area, ended with no major catastrophe, as the DWR managed the lake’s levels with limited, controlled releases on the main spillway until the water subsided.

The Causes

In their report, Bea and Johnson enumerate five design issues, two construction issues and two issues with the maintenance and operation of the dam that they say ultimately led to February’s failure of the main spillway.

The physical causes, the engineers say, included:

  • Concrete base slabs that were too thin for the structure;
  • Insufficient steel reinforcement of the base slabs;
  • A lack of effective water stop barriers on both sides of joints in the slabs;
  • Ineffective ground anchors keeping the slabs from moving;
  • Failures to properly prepare the ground underneath the slabs at the time of construction in order to prevent water collection and erosion;
  • Ineffective repairs to cracks and joint displacements over the years since construction; and
  • Trees that were allowed to grow near the spillway, potentially affecting drainage pipes with their root systems.

The report goes on to say that the organizational root causes stem from a failure on the part of the DWR and other parties, including the Federal Energy Regulatory Commission, to seriously investigate potential problems at the dam. “A superficial ‘Patch and Pray’ approach is not an acceptable Safety and Risk Management Process for important public infrastructure Systems,” the authors note.

slab issues

Physical causes of the February crisis, the engineers say in the report, included failures to properly prepare the ground underneath the slabs at the time of construction in order to prevent water collection and erosion, and trees that were allowed to grow near the spillway, potentially affecting drainage pipes with their root systems.

The report focuses on the original damage to the main spillway at the dam, and does not examine the chain of events that led to the auxiliary spillway failing as a backup plan.

Headgate Corrosion, ‘Green Spots’

Bea, who has studied catastrophic failures including the Deepwater Horizon disaster and the Challenger explosion, also told the University of California’s alumni magazine, California, that he has concerns about corrosion and cracks in the headgates of the dam, and about patches of green vegetation on the abutments, which he believes indicate water seepage.

Erin Mellon, spokesperson for the DWR, told SFGate that "Mr. Bea's report suggests that the green spots are the result of cracking of the core from differential settlement and resulting leakage from the reservoir. These green spots were first noticed just after construction of the dam when there wasn't even water in the reservoir.

Rebar corrosion

The report also cites ineffective repairs to cracks and joint displacements over the years since construction.

"The preliminary finding from DWR's inspections and studies show that this is an area that collects water from rainfall causing vegetation to grow."

Bea, however, told California, “A ‘natural spring’ in that area would have to flow uphill, which runs counter to the laws of physics. And understand this: Any seepage through an earth-fill dam is extremely worrisome.”

In the report summary, the authors note that the physical issues that led to February’s crisis “have been consistent with those from a large number of previous forensic investigations of failures and disasters associated with engineered infrastructure systems.

“It is the human and organizational factors that are the primary challenge to being able to develop safe and reliable engineered infrastructure systems.”

Construction Timeline

Last week, all pertinent government agencies gave approval to the DWR and lead contractor Kiewit to expedite repairs to the main spillway in order to meet the two-year timeline for the overall project.

DWR had made the request in mid-July, seeking permission to replace an additional 240-foot stretch of the main spillway this year. The agency said Kiewit reported that "demolition to station 20+30 must commence as soon as possible to meet the project schedule.”

   

Tagged categories: concrete; Corrosion; Government; Locks and dams; NA; North America; Program/Project Management; Rebar

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