Use of vibrating wire strain gauges to measure loads in tubular steel props supporting deep retaining walls

Prop loads in braced excavations are often monitored using vibrating wire strain gauges attached to the prop and are generally found to vary significantly with temperature. In this paper, the interpretation of strain gauge data to determine axial loads and bending moments in tubular steel props is described with reference to measurements made during the construction of London Underground Limited’s Jubilee Line Extension stations at Canada Water and Canary Wharf. Temperature and end effects are discussed, the accuracy and potential shortcomings of the technique are assessed, and guidelines for the achievement of accurate and reliable results are suggested.