Stressed steel tendons have been used to strengthen hydraulic structures and to improve their serviceability and stability. Over the past three decades, the US Army Corps of Engineers has worked to upgrade its projects by installing high-capacity, post-tensioned foundation anchors. The goal has been to achieve structural stability for Corps hydraulic concrete structures and/or to remediate cracked concrete monoliths. Substantial improvements to protect multistrand anchor systems from corrosion have been made since they were first used at Corps projects more the 50 years ago. Corrosion of older multistrand units is of concern.Researchers at the US Army Engineer Research and Development Center (ERDC) are looking to develop engineering procedures to estimate the current state of load-carrying capacity of the ground anchorage, to estimate remaining life of the tendon, and to establish the deterioration of anchorage capacity (with time) so costly replacement of ground anchorage can be delayed until absolutely needed. Analytical, laboratory, and field-testing efforts will be used to develop a methodology and analytical models. Probabilistic procedures will be used to quantify uncertainties for the primary variables and will be carried into the analytical model. Procedures to extend the life of deteriorating multistrand tendons also will be investigated.A review of Corps projects using multistrand anchors and a literature review of corrosion of the anchors are summarized in this report. Also included are the history and performance of the multistrand anchors at the John Day Navigation Lock (Columbia River, Portland District), along with postinstallation lift-off test results. A summary of a review of nondestructive testing (NDT) to identify defects in the anchors is part of this report, too.

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BACKGROUND: A Research Work Unit (WU) has been initiated in the Navigation Systems Research Program to investigate post-tensioned multistrand anchors. A significant number of COE projects have installed multistrand high-capacity post-tensioned foundation anchors over the last three decades. These anchors are embedded and access is limited to the top anchor head for inspection purposes. Due to the evolution of corrosion protection criteria for ground anchors, the early installed anchors may have inadequate corrosion protection that does not meet current corrosion protection standards. The older anchors are approaching the end of their design life and are showing various degrees of deterioration, corrosion, and broken strands. Current load capacity and remaining life of the anchors are unknown. One procedure used to test post-tensioned tendons involves lift-off tests, which are both dangerous and expensive. The applicability of lift-off testing to most existing ground anchorage is severely restricted to the very few existing ground anchors that were not grouted for corrosion protection along the free length of the anchor and which also have special provisions for the connection of the jacking equipment to the anchor head. This severely restricts the practical use of lift-off testing of existing ground anchorage as a viable testing procedure. Additionally, testing deteriorated anchors has been avoided in the past because of greater danger of breaking anchors. To meet reliability analysis required for major rehabilitation studies, estimates of load capacity, rate of decrease, and remaining life are required.

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