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45 consumed within 10 years, and the base steel will be consumed of Equation (27) does not apply to degradation from hydrogen at a rate of 28 m/yr per side thereafter. Although the zinc life embrittlement or SCC. In these cases, service lives are severely is relatively short, the main purpose of the zinc is to mitigate compromised if the reinforcements are exposed and in contact the development of macrocells and promote more uniform with the surrounding soil or rock mass, particularly for corrosion. For tf of 50 years, the nominal sacrificial steel environments that are acidic or high in chlorides. Therefore, requirement according to Equation (29) is 2.24 mm (i.e., X = high-strength steel reinforcements must be isolated from the 1120 m/side). If Equation (29) is the basis for computing the environment via a corrosion protection system. In these cases, nominal sacrificial steel requirements, a resistance factor of a double corrosion protection system (Class I) is recommended 0.30 is recommended for LRFD and the yield limit state. and the service life is governed by the quality and detailing Type II reinforcements include rock bolts and ground inherent to the double corrosion protection system. Data were anchors. Due to the fact that these reinforcements are often collected during this research from one site with high-strength surrounded by grout or protected via a single (Class II) or dou- steel reinforcements and a double corrosion protection system. ble (Class I) corrosion protection system, only the portions These data indicate that the corrosion protection system at this of the assembly that are exposed and in contact with the site is intact and performing well; a grease-filled trumpet head surrounding environment are vulnerable to corrosion. Due to is included with the anchor head assembly. fundamental differences in the materials, installation details, and workmanship applied to rock bolts versus ground anchors, Recommendations for the reliability inherent to service life estimates of these installa- Asset Management tions is described separately. For rock-bolt installations, the most vulnerable locations Asset management is an important issue facing highway are behind the bearing plate, which often includes a gap, or operations, and forecasting the needs for maintenance, retrofit, other locations where the reinforcement is not completely or replacement of existing facilities is an important component surrounded by grout or is otherwise left unprotected. Metal of transportation asset management (TAM). Earth-retaining loss is a concern at these locations, and previous design guid- structures should be included in a TAM program along ance has not directly considered metal loss in the considera- with pavements, bridges, ancillary structures, and so on, to tion of service life. However, resistance to pullout, rather than help ensure optimal usage of limited available funding (FHWA, rupture resistance, often controls the lock-off load for rock- 2008). Properly defining the existing inventory and the devel- bolt installations; therefore the resistance of the reinforce- opment of a performance database are important components ment section may not be fully mobilized at any time during of asset management. Relatively rapid, nonintrusive, and non- the service life. Chapter 3 includes an example from a site destructive test techniques are needed to collect data necessary where pullout resistance controls the lock-off loads and data for corrosion monitoring and condition assessment of earth- on metal loss of Type II reinforcements, available from the lit- retaining structures. Results from condition assessment and erature, are used to assess the resistance bias at the end of the corrosion monitoring indicate when, or if, accelerated corro- design life. The example demonstrates that for the selected sion is occurring and can help transportation agencies decide site, metal loss is not a significant concern for service lives less on the most appropriate course of action when subsurface con- than 75 years. A resistance factor for the rupture limit state ditions are unfavorable and service life is uncertain. Agencies and a 100-year design life is computed as 0.55, corresponding can also use these data to evaluate the variance associated with to a target reliability index of 3.12 and pf 0.001. This exam- the performance of an inventory; this is valuable information ple demonstrates how the statistics generated from metal loss for those with an interest in making reliability-based decisions. measurements can be used to calibrate resistance factors for This report describes the framework of a performance database LRFD of Type II reinforcements. However, the computed useful for asset management, test techniques and protocols that resistance factor is sensitive to the lock-off load, and depends are being employed to collect performance data for earth rein- on the sizes and steel types of the reinforcements. forcements, data interpretation, and preliminary information If lock-off loads are controlled by rupture (rather than pull- available from data that has been collected to date. out resistance), then sacrificial steel requirements must be con- sidered explicitly. Equation (27) is recommended to compute Performance Data nominal sacrificial steel requirements. Resistance factors can then be calibrated using the statistics describing metal loss The performance database includes thousands of mea- measurements from Type II reinforcements cited in Chapter 3. surements of element conditions and corrosion rates from Ground anchor systems that use high-strength steels with more than 150 sites distributed throughout the United States GUTS in excess of 150 ksi are vulnerable to other forms of cor- and Europe. The large sample domain allows evaluation of rosion that may include hydrogen embrittlement and SCC. Use sample statistics, distributions of element conditions and