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A test embankment was built in the James Bay region to establish the behavior of the lacustrine clay in the area with respect to the prediction settlement under earth and/or rockfill structures.The clay deposits are characterized by high sensibility (7–25), low shear strength (Cu = 400 p.s.f. (0.2 kg/cm 2 )), high compressibility (Cc/(1 + e 0 ) = 0.6–0.9) and geological belong, to the normally consolidated type of the material. Nevertheless these clays exhibit an important 'quasipreconsolidation' behavior due to the phenomenon of delayed consolidation.The results of post construction surveys and observations taken during a period of 8 months have confirmed the characteristics already established by laboratory tests and particularly the high compressibility and the 'quasipreconsolidation pressure' of these clays.The measured settlements to date (18 in. (45 cm)) can be attributed in the following proportions, 70% to secondary consolidation, 22% to elastoplastic creep, and 6% to lateral creep.In the above mentioned period, practically no pore pressure dissipation was observed and consequently no settlement due to primary consolidation was considered.The results gathered seem to confirm the applicability of the settlement calculation method of the Bjerrum soil model, however, the rate of settlement computation using the classical method is very difficult if not impossible to calculate. The simultaneous developments of primary and secondary consolidation and the greater contribution of the latter to the total value of settlement does not permit the use of the classical method based on the pore pressure dissipation.The method proposed lately by Garlanger needs more development to permit the analysis of a multi-layered foundation with different compressive and preconsolidation characteristics.The stress and strain computation using the finite element method considering the foundation as an isotropic elasto-plastic medium seems to give satisfactory results at least for the range of stresses and the direction of deformation considered.
Dascal et al. (Wed,) studied this question.