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12 CHAPTER 2 Research Approach Tasks predicting the corrosion potential, metal loss, and service life of metal-reinforced systems in geotechnical applications. The research approach includes nine tasks and the project was conducted in two phases. Tasks 1 through 5 were included in Phase I, and Phase II includes Tasks 6 through 9. Results Task 4--Develop Work Plan from Phase I were described in the project interim report that for Field Investigation was submitted in April 2007, and this report includes results Task 4 consists of preparing detailed plans for a compre- from Phase II. A brief description of tasks from Phase I is hensive field investigation to evaluate the performance of summarized to help place the approach and results from earth reinforcement systems. This plan addresses some of the Phase II into context. deficiencies in the performance database identified in Task 2. These deficiencies include limitations with respect to geo- Task 1--Literature Review and Survey graphic distribution, range of fill characteristics, spatial and temporal variations, and corrosion rate measurements for Task 1 consists of a review of existing literature and a sur- Type II reinforcements. vey of owners, designers, and contractors to (1) identify exist- ing data on the past performance of metallic reinforcements; (2) trace the development of corrosion potential, metal loss Task 5--Submit Interim Report and service life models that form the basis for the existing Task 5 consists of preparing an interim report summariz- AASHTO specifications and FHWA recommendations; ing the results, conclusions, and recommended work plans (3) document information relative to existing installations; developed during Tasks 1 to 4. This report was submitted to and (4) solicit information regarding existing sites and planned and approved by NCHRP in April 2007. construction/deconstruction where access to reinforcements could be gained for field studies, including opportunities to Task 6--Implement Field Investigation exhume reinforcement samples for observation and testing. Task 6 consists of implementing the workplan developed Task 2--Prepare Performance Database in Task 4 and approved in Task 5. Task 2 consists of (1) developing and populating a database Task 7--Identify Target Reliability Index using existing performance data identified in Task 1, (2) col- for LRFD lecting information regarding the existing inventory of metal- lic earth reinforcements, and (3) studying attributes of the Using the data from Tasks 2, 3 and 6, statistical properties performance data and comparing attributes of the general are computed to describe the variability of factors that affect population to those from sites with performance data. metal loss and service life estimates of in-ground metallic reinforcement systems. This includes (1) reevaluation of the Task 3--Estimate Reliability prediction model(s) to assess its accuracy and precision to esti- of Service-Life Models mate metal loss caused by corrosion and (2) development of appropriate resistance factors for use in LRFD that account for Task 3 consists of analyzing the results from Tasks 1 and 2 metal loss caused by corrosion. Calibration of the resistance fac- to estimate the reliability and utility of promising models for tors uses load factors from the AASHTO LRFD specifications