Long-Term Force Monitoring of Pre-stressed Anchors used on Dam Rehabilitation Projects

Maintenance and health monitoring of aged dam structures has been of particular concern to the engineering community. Many dams are being retrofitted using pre-stressed anchors. There are few testing methods available to assess the forces in these anchors once installed. High cost, complicated equipment, unreliability and limitation of space often prevent these methods from being implemented. DSI has been involved in the development, testing and utilization of DYNA Force® sensors to measure the forces in the anchors. These sensors make use of the magneto-elastic properties of ferrous materials. A readout unit is designed to magnetically energize the steel through the sensor and measure response of the steel to the process. The readout unit then converts response into a direct force reading. Its application in ground anchors of six prominent dam rehabilitation projects is presented here. The sensors were used to monitor the force in the ground anchor during load testing and long-term behavior of the anchor. Data collected manually and remotely are providing valuable information to the engineer.
DYNA Force sensors have received attention in terms of accuracy, ease of installation, durability, and cost effectiveness. They were used in over sixty projects. This paper describes its application on rock anchors of prominent dam rehabilitation projects, including Willow Island Hydroelectric Project in WV, Roanoke Rapids Lake Dam and Lake Cammack Dam in NC, Byllesby dam in Minnesota and Cherokee and Douglas dams in Tennessee. The sensors were used to monitor the force in the ground anchor during load testing and long-term behavior of the anchor. The sensors are being used for future anchor load monitoring both manually and remotely at preset intervals and are providing valuable information to the engineer. Sensor is proven to be a great tool for inspection of critical structures in a few minutes. Data from these five dams is presented.