Load Monitoring of Ground Anchors Using Contact Free Sensors

Our infrastructure is expanding and the existing infrastructure is aging. Most structures are expensive to maintain and some occasionally fail. A large number of retaining walls, bridge abutments, dams, tunnels, and other geotechnical structures use pre-stressed ground anchors. Many existing structures require installation of pre-stressed anchors as an upgrade. Force monitoring of these anchors is crucial during construction and for long term behavior of structure. Among available instruments strain gauges, load cells, or fiber optics are pre-installed. Mounting of strain gauges and fiber optics are challenging. If load cells are used, it will require larger and deeper block-out to stress and accommodate the end cap. Most do not provide reliable data after few years in service. The most reliable method is to use elasto-magnetic sensor which does not require the sensor to be attached to the steel. They have been used successfully in over 80 projects. Sensors receive attention in terms of accuracy, performance, ease of installation, durability, and cost effectiveness. This paper describes its application in tie-back force monitoring, force transfer in bond zone, anchor force monitoring during excavation of rocks and tie force monitoring in tunnel construction.