LRFD Metal Loss and Service-Life Strength Reduction Factors for Metal-Reinforced Systems in Geotechnical Applications

Transportation agencies use a variety of metal-reinforced systems in geotechnical applications, including soil and rock reinforcements, ground anchors, and tiebacks. These systems support retaining walls and soil and rock slopes and stabilize roadway cuts and fills. The precise conditions governing the deterioration of these systems are uncertain, but corrosion is known to have an impact on their service life. Engineers, faced with the task of allocating budgets to rehabilitate aging facilities, need reliable techniques for assessing corrosion and estimating metal loss. Service-life estimates for new systems need to be improved, and consideration of metal loss in their design needs to be consistent with the reliability-based approach adopted in the AASHTO LRFD (Load and Resistance Factor Design) Bridge Design Specifications. The current LRFD specifications do not adequately address factors that affect the service life of metal-reinforced systems, particularly with respect to the effects of climate, soil environment, metallurgy, and installation details. Calibration of the resistance factors for metal-reinforced systems requires data describing their subsurface environment, metal type (metallurgy), level of corrosion protection afforded to the system, and the prevailing mechanisms of their corrosion (e.g., uniform galvanic action, localized pitting, stress cracking, hydrogen embrittlement, microbial, and stray currents). The corrosion studies conducted by National Bureau of Standards (now the National Institute of Standards and Technology) since the early 1900s are well documented. However, the data obtained from these long-term monitoring programs--that used weight-loss measurements on mild, carbon-based steel coupons embedded within fill-type soils--have limited applicability to modern metal-reinforced systems. The research proposed here will include field investigations employing new technologies for corrosion assessment and nondestructive testing (NDT) of the metal-reinforced systems. These technologies allow the effects of different factors to be assessed within a relatively short timeframe for systems installed within fills, in-situ soils, and rock. Further, development of appropriate resistance factors that may be calibrated for LRFD requires quantification of the uncertainties associated with the reliability of estimates of service life that account for the potential loss of section from corrosion. These uncertainties can arise from modeling errors and the measurement of soil/rock input parameters as well as from relationships between the intended service life, soil environment, climate, installation details (including corrosion protection afforded to the system), methods of sampling and testing backfills or native soils, and modeling errors. The results of this project will address a strategic objective of the AASHTO Highway Subcommittee on Bridges and Structures (HSCOBS): to fully implement LRFD through enhanced specifications for improved structural performance. The objectives of this project are to (1) assess and improve the predictive capabilities of existing computational models for corrosion potential, metal loss, and service life of metal-reinforced systems used in retaining structures, highway cuts and fills, and other applications; (2) develop methodology that incorporates the improved predictive models into an LRFD approach for the design of metal-reinforced systems; and (3) recommend additions and revisions to the AASHTO LRFD specifications to incorporate the improved models and methodology.

Language

  • English

Project

  • Status: Completed
  • Funding: $600000.00
  • Contract Numbers:

    Project 24-28

  • Sponsor Organizations:

    Federal Highway Administration

    1200 New Jersey Avenue, SE
    Washington, DC  United States  20590

    American Association of State Highway and Transportation Officials (AASHTO)

    444 North Capitol Street, NW
    Washington, DC  United States  20001

    National Cooperative Highway Research Program

    Transportation Research Board
    500 Fifth Street, NW
    Washington, DC  United States  20001
  • Project Managers:

    Harrigan, Edward

  • Performing Organizations:

    McMahon & Mann Consulting Engineers, P.C.

    ,    
  • Principal Investigators:

    Fishman, Kenneth

  • Start Date: 20060601
  • Expected Completion Date: 0
  • Actual Completion Date: 20100630
  • Source Data: RiP Project 11794

Subject/Index Terms

Filing Info

  • Accession Number: 01462943
  • Record Type: Research project
  • Source Agency: National Cooperative Highway Research Program
  • Contract Numbers: Project 24-28
  • Files: RiP, USDOT
  • Created Date: Jan 3 2013 2:13PM