Effects of construction-induced stresses on dynamic soil parameters of bootlegger cove clays

This paper presents the influence of construction-induced stress changes on the dynamic soil parameters of Bootlegger Cove Formation (BCF) clays at the site of the Port of Anchorage (POA) expansion project. Results are presented based on numerical simulations of the POA wharf construction and laboratory experimentation where both free-field and postconstruction conditions are reproduced. The postconstruction stability of the foundation clay is considered under both static and dynamic loadings. For the dynamic case, a cyclic triaxial loading equivalent to the contingency-level earthquake (CLE) established for design was used, whereas for the static case, undrained triaxial compression and extension loadings to failure were employed. The results from numerical simulations and laboratory experiments are presented and compared with field measurements and performance data collected during the project construction. The results obtained from specially designed cyclic triaxial probes show the large effects that the construction-induced stresses can have on the dynamic soil parameters and illustrate the importance of adequately considering such effects. Testing protocols and procedures are proposed for quantifying postconstruction soil parameters to better reflect field values and values at small (and otherwise appropriate) strain levels.