Validation of LRFD Metal Loss and Service-Life Strength Reduction Factors for Metal-Reinforced Systems (2011)

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PROPOSALS FOR POSSIBLE FUTURE RESEARCH 1. The techniques for measuring fill resistivity implemented in this study should be applied to the database developed for NCHRP Project 24- 28 to develop service-life models that directly incorporate fill resistivity as a variable. Current service-life models used to calibrate LRFD strength-reduction factors in NCHRP Project 24-28 apply to relatively broad ranges of fill types (resistivities) leading to wide scatter and variability within the range of marginal qual- ity fills. Service-life models that directly incor- porate fill quality will yield improved correla- tions between corrosion rate and fill resistivity, and improvements to reliability-based calibra- tion of LRFD strength-reduction factors for MSES constructed with marginal quality fills. 2. More data should be collected to document the performance of MSES constructed with mar- ginal quality fills. The characteristics of mar- ginal quality fill including salt contents and resistivities may vary randomly with respect to location within a given source. Fill resistivity may change over time due to changes in mois- ture content, salt concentration, etc., and these changes are not described by measurements on fill sources obtained prior to construction. Thus, data should be collected from selected sites at prescribed intervals to monitor spatial varia- tions and the effects of changes in conditions that may occur over time. These data would be useful to provide guidance, recommendations, specifications, and limitations on use of mar- ginal quality fills for construction involving earth reinforcements. 3. The IR test is recommended for condition assessment of rock bolts when more detailed information from within the bonded zone is necessary. Further evaluations should be conducted for rock bolt lengths greater than 20 feet. 4. Additional data on the performance of rock bolts should be collected and used to develop fragility curves to describe the time-dependent vulnerability and safety of rock cuts that are supported with rock bolts. REFERENCES Davis, A. G. and Robertson, S. A. (1975). “Economic Pile Testing,” Ground Engineering, London, United Kingdom, pp. 40–43. 6

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