Elastic Shear Modulus of Compressible Chicago Clay

This paper summarizes the results and analyses of laboratory and field measurements of the elastic shear modulus of lightly overconsolidated, compressible Chicago clays. These soils are glacially-derived, freshwater ice margin deposits. The laboratory experiments were conducted on twelve high quality block samples obtained from three excavation sites in the Chicago area. The specimens were consolidated to in situ stresses via a recompression technique, and the elastic shear modulus was synchronously obtained from results of bender element tests during consolidation and subsequent creep. Seismic cone penetration and crosshole seismic tests were performed in situ. The results show that the elastic shear moduli from the bender element tests after consolidation and a sufficiently-long creep period are approximately the same as those obtained from the results of the in situ tests. The effects of time on the elastic shear modulus are smaller than the effects caused by soil variability. Evaluation of the laboratory and field data indicates that the elastic shear modulus of compressible Chicago clays can be estimated from the natural water content and mean normal effective stress.