68th Canadian Geotechnical Conference and 7th Canadian Permafrost Conference

EVALUATION OF THE UNDRAINED SHEAR STRENGTH OF CHAMPLAIN SEA CLAYS (LEDA CLAY) IN OTTAWA USING CPT

Session: In Situ Testing and Instrumentation I / Essais in situ et instrumentation I

Raymond Haché, M.Sc., P.Eng., ing. (Canada)
Athir Nader, M.A.Sc., E.I.T. (Canada)
Simon Gudina, Ph.D., P.Eng. (Canada)
Mamadou Fall, Ph.D., Dipl.Eng., Dipl.Eng. (Canada)

An evaluation of the empirical cone factors, Nkt, which are used to define the undrained shear strength (su) profile of a deposit on the basis of cone penetration test (CPT) has been carried out for eleven Ottawa Leda clay sites. Both CPT and field-vane tests were carried out at each site as part of the evaluation of the Nkt values. The field-vane apparatuses used were friction compensated digital and Nilcon vanes. Nkt values presented in the literature typically range from 10 to 20 with recommended values of 14 to 16 in the cases where site specific information is not available. The Ottawa Leda clay sites investigated mostly produced Nkt values in the range of 8 to 12. The practice of using SPT N-values to estimate the undrained shear strength is also briefly discussed and it is demonstrated to be unsuitable for use within Leda clay deposits.