: Implementing Lifecycle Characterization of Embedded Dam Gate Anchorage Using Non-Destructive Testing and Structural Health Monitoring

Description

Background: U.S. federal and state government agencies manage and operate an inventory of dams that protect property, environment, and lives from floods, facilitate navigation along the U.S. river systems, provide water supply, create opportunities for hydropower generation, and create lakes for recreation use. Dam spillway gates are important components of a dam. They allow control of pool elevation along rivers and allow control of water during a flood event. Many spillway gates use post-tensioned anchor rods embedded into concrete during construction. After many years, the safety and reliability of these anchor rods is in question, as their deterioration may result in failure of the dam to serve its intended purpose, possibly leading to loss of life or major economic impacts. Unfortunately, these rods are mostly inaccessible for inspection, being embedded in concrete. Recently, several non-destructive testing (NDT) methods have been developed for finding cracks or flaws on an embedded gate rod or determining the tension in existing ungrouted rods. However, it is not clear how these variables impact dam reliability nor how/when to remediate rods to increase reliability where appropriate. Information is even less clear for grouted type rods. There is a need to understand the lifecycle of embedded anchor rods such that efficient, effective, and proactive maintenance and repair strategies can be programmed and implemented to increase the national safety and reliability of the dam inventory. Recent research has been conducted which laid out a plan to finalize trunnion rod lifecycle characterization methods and provide an implementable NDT and assessment technique. Preliminary work was conducted along that play, but the full effort is still needed. Brief Description of Anticipated Work: The purpose of this research is to characterize the lifecycle of embedded dam gate anchorage such that risk can be assessed and managed efficiently and effectively by dam owners and to finalize an implementable technique for dam owners. Specifically, the objectives include: Objective 1: Characterize dam gate anchorage lifecycles, specifically ungrouted trunnion rod anchorage commonly found on river and reservoir dam spillway gates for the purposes of assessing risk and reliability. The lifecycle should consider all relevant geometric, material, operational, and environmental variables in its definition. The lifecycle should describe clearly a measure of reliability of anchor rods, or groups of anchor rods if more appropriate, as a function of time given current conditions/knowledge. Uncertainty of all variables should be included and appropriately propagated through the lifecycle description to the outputs of reliability. The lifecycle should be able to be used by dam owners to assess degradation rates and plan maintenance and remediation strategies proactively. Physical and numerical modeling may be required for this and other objectives as may field measurements at U.S. dam sites.Objective 2: Identify information and observations about the current conditions that can be procured to reduce uncertainty in the lifecycle. These may be from structural health monitoring technologies or testing, whether destructive or nondestructive (NDT), such as guided waves, ultrasonic methods, pull-off tests, or others. Develop a methodology for updating a lifecycle with this new information and a “value of information” process by which a dam owner can decide whether to “purchase” this new information. Provide information about frequency of updating information if deemed appropriate.Objective 3: Identify remediation or repair strategies that can have a positive effect on the lifecycle and demonstrate through examples how an engineer or dam owner would use the lifecycle to decide on a best course of action. These strategies could be to isolate certain environmental effects, reduce anchor tension, replace anchors, etc.Objective 4: Investigate the applicability of existing NDT methods to grouted trunnion rod anchors as well as how a grouted rod lifecycle may differ from that of an ungrouted rod. Previous work has established a technical development roadmap, which should inform the technical approach for this research. The existing technical development roadmap is:Task 1: Review previous research conducted by USACE relevant to grouted and ungrouted trunnion rod assessment and NDT.Task 2: Identify and describe potential failure modes specific to post-tensioned anchor rods, both grouted and ungrouted.Task 3: Estimate likelihood of post-tensioned anchor rod brittle failure due to stress corrosion cracking, considering existing methods of identifying defects and performing necessary analytical modeling.Task 4: Develop anchorage analysis methods under variable post-tensioned rod loads, utilizing finite element analyses calibrated as necessary.Task 5: Conduct laboratory testing to validate numerical models.Task 6: Develop a simplified method to estimate likelihood of rod failures.Task 7: Characterize ungrouted trunnion rod anchorage lifecycles with respect to risk and reliability assessment.Task 8: Identify information and observations about the current conditions that can be procured to reduce uncertainty in the lifecycle, considering structural health monitoring and NDT used update lifecycle models.Task 9: Identify remediation or repair strategies and their expected impact on lifecycle performance.Task 10: Investigate the applicability of existing NDT method to grouted trunnion rod anchors as well as how a grouted rod lifecycle may differ from that of an ungrouted rod.

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