Measuring Instruments for Strutted Excavations

Since 1955 the Norwegian Geotechnical Institute has been actively interested in problems concerning the design and construction of strutted excavations in both soft and stiff-fissured clays. One of the first steps taken was to initiate a comprehensive program of instrumentation and observation of different excavations in Oslo. The results of this program have proved to be valuable. To encourage similar instrumentation programs that could be of value to engineers working with similar problems, a description of the instruments and techniques used in Norway to measure strut loads, earth and water pressures, and movements is presented together with information concerning the cost, accuracy, and reliability of these instruments. Examples of successful use on jobs is presented. The Institute's experience indicates that design procedure commonly used are not applicable to all site conditions. Important, if not dominant effects are shown to result from temperature, and construction procedures and sequences, factors that cannot be predicted analytically for design. The cost of the struts are shown to be minor compared to the other excavation factors.