The Modulus of Elasticity of Leda Clay from Field Measurements

The construction of the Ottawa Sewage Treatment Plant provided an opportunity to measure bottom heave in two large excavations in clay. With gauges installed prior to excavation, elastic heave, swelling, and heave due to pile driving were measured in an excavation 31.5 ft. deep. Using a Poisson's ratio of 0.4, the modulus of elasticity determined from field measurements compared favourably with the initial tangent modulus from the best unconfined compression strength tests. In the other excavation a drop in the ground water table produced an elastic settlement that exceeded the elastic heave resulting from unloading by excavation.