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Abstract:
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A large rigid circular raft has been instrumented to study its foundation performance in the Leda Clay of the Ottawa region. The raft which supports a tower farm silo has a diameter of 13.7 m (45 ft) and a thickness of 1 m (3.28 ft). Comprehensive laboratory and field measurements were performed. All the laboratory tests including, CIU triaxial and oedometer, as well as the field vane shear strength tests were carried out by the staff of NRC, DBR. The other measurements which included: normal contact pressure distributions, settlement and pore-water pressures at various depths and the deflection of the raft were carried out by the University of Ottawa in cooperation with NRC, DBR. The measurements have been analyzed and where possible the results of the analysis compared to theory and to case records. In addition, the load settlement data for six square footings and four test plates also in Leda Clay, have been analyzed; and the results compared to those for the silo raft. The plate and footing measurements were carried out by the Geotechnical Group of the University of Ottawa at Algonquin College, Woodroffe Campus, in Ottawa. The outcome of the research programme includes the following: (a) recommended ranges of Eu/Su values applicable to most foundation elements founded in Leda Clay of the Ottawa area; (b) settlement distribution curves which appear to be a characteristic of the clay, and (c) design recommendations concerning normal contact pressures and the modulus of subgrade reaction. All the above recommendations apply when the soil is loaded below its preconsolidation stress. Finally, a list of suggestions for further research work is brought forward. |
