CASE-HISTORIES ILLUSTRATE THE IMPORTANCE OF SECONDARY-TYPE CONSOLIDATION SETTLEMENTS IN THE FRASER-RIVER DELTA

The technique of preloading the deep, compressible soils in the Fraser River delta has been used for more than 40 years to prevent excessive settlement of major structures. This paper documents 22 years of sett lement under preloading and after construction of the facilities for a major waste water treatment plant in the delta. These results are sim ilar to observations for as long as 28 years at five additional sires in the delta. it was found that as much as one half of the measured su rface settlement occurred during or within a few weeks of the full app lication of the preload and that subsequent settlements have the chara cteristics of secondary consolidation. This could not have been predic ted from laboratory tests, and it raises questions concerning the true nature of consolidation in situ. For practical purposes the observati ons provide guidance for the prediction of long-term settlements in th e region.