River Road Forensic Analysis

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River Road Forensic Analysis
Montgomery County Council Transportation,
Infrastructure, Energy and Environment
Committee June 8, 2009
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Analysis of 66 PCCP Rupture
Failed Pipe No. 20
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Typical PCCP Configuration
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ANALYSIS

• Lewis Engineering and Consulting (Gainesville,
  FL) contracted in January 2009 to conduct
  forensic analysis
• Conducted site visits and field inspections
• Obtained samples from all damaged pipe sections
• Conducted lab tests and microscopic examinations
• Reviewed design, construction and manufacturing
  specifications, mechanical properties circa 1965
• Reviewed operating conditions

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FINDINGS

• Rock contact occurred either during construction
  resulting in immediate cracking of the coating or
  it developed at the later date due to
  point-loading on rocks caused by overburden and
  improper bedding
• Examination of pipes 13, 18 and 21 found internal
  cracks, distress with external coating damage,
  corroded and broken presstressing wire in the
  same relative 730 oclock orientation
• Corrosion-induced failure of more than 100
  contiguous circumferential wraps of prestressing
  wire
• Corrosion of prestressing wire and external
  surface of steel cylinder ongoing for many years,
  even decades

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FINDINGS
Rock Removal During Repairs
Rock Removal under Pipe 18
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FINDINGS

• WSSC General Specifications adopted in Sept. 1954
  and applicable to 1965 construction required
  removal of rock from pipe trench, placement of
  select bedding material free from rock in the
  trench bottom to provide uniform and continuous
  bearing support along its length
• WSSC staff reports and documented evidence from
  the repair site confirm the pipe bedding
  conditions were not compliant with WSSC General
  Specifications adopted in Sept. 1954 and
  applicable to 1965 construction
• Responsibility for the pipe having been installed
  on incompletely excavated rock and improperly
  prepared bedding lies with installation
  contractor

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FINDINGS

• Based on findings, rock bedding conditions may be
  possible along route of remaining 66-inch
  pipeline
• Additional sections of pipe beyond those removed
  and replaced may be subject to similar conditions
• All PCCP materials used to manufacture are
  compliant with 1965 Interpace Pipe Design
  Specification Sheet

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CURRENT WSSC ACTIONS

• Continue the investigation
• Annual inspection plan based on risk rating
  assigned to 36 and larger (145 miles). Risk
  rating based on pipe diameter, age, land use,
  operational criticality, repair history and date
  last inspected.
• Program focuses on mains 48-inch and greater.
  Considered a higher risk due to their diameter,
  operational criticality and higher consequence of
  failure.
• Current state of the industry for non-destructive
  PCCP inspection techniques requires manual
  operation and manned entry into the pipelines

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CURRENT WSSC ACTIONS

• Techniques for unmanned inspections of 42-inch
  and smaller are emerging
• Preferred inspection interval for PCCP pipelines
  is 5 to 10 years 5 years for 48 and above to 10
  years for below 48
• FY07 and FY08 PCCP Program mileage budget was 6
  miles inspection and 6 miles of installation of
  Acoustical Fiber Optic (AFO) monitoring results
  in inadequate and high risk 12 year inspection
  interval
• At 12 miles per year, the 48 and larger
  pipelines would be on a near optimum inspection
  interval of just over 6 years 

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FY 09 ACTIONS

• In FY09, the Counties approved budget supplement
  to increase PCCP inspection mileage to 12 with
  installation of Acoustic Fiber Optic (AFO)
  monitoring
• Beginning of five-year plan
• (Since Jan. 09) Inspect Project 80 96
• Inspect Montgomery County Failed 48
• Budget for inspection 2.5 Million

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FY 10/11 ACTIONS

• FY 10
• Inspect Rock Creek 54/60 and River Road 66
• Initial budget for inspection 2.5 Million
• Additional 1 million provided at approval of
  budget
• Intend to use part of funding on failed 42 in
  January
• FY 11
• Inspect Montgomery County High Zone 60
• Inspect White Oak 72
• Evaluate 60 Adelphi for Rehabilitation

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QUESTIONS?