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 settlement under preloading and after construction of the facilities for a major waste water treatment plant in the delta. These results are similar to observations for as long as 28 years at five additional sites in the delta. It was found that as much as one half of the measured surface settlement occured during or within a few weeks of the full apllication of the preload and that subsequent settlements have the characteristics of secondary consolidation. This could not have been predicted from laboratory tests, and it raises questions concerning the true nature of consolidation in situ. For practical purposes the observations provide guidance for the prediction of long-term settlements in the region. Key words: case history, consolidation, field observations, preloading, settlement.