A project to assess possible compression of near surface soils beneath a constructed embankment and the likely reduction in regional (horizontal) flow through this depth of soil yielded quite surprising behavior. This silty sand (with non- to slightly plastic fines) yielded lower SPT blow counts and was, in fact, characterized by the commonly employed CPT tip and sleeve correlation program as fine-grained (silt-clay) soil. However, piezocone readings showed negative pore pressures during field penetration, while triaxial tests on "undisturbed" and reconstituted samples showed drained volumetric expansion or negative undrained pore pressures during shear. Furthermore, in situ void ratios based on water contents in relation to lab established maximum and minimum void ratios indicated medium to very dense in situ conditions, different from the loose to medium conditions established from commonly employed SPT blow count correlation. Low field and laboratory permeability test results indicated the likely development and dissipation of excess pore pressures due to end of construction conditions. However, this did not prepare the investigators for the water level changes recorded in piezometers located beneath versus adjacent to the 30-foot high fill constructed at the Zolezzi Lane site.
