Utilization of unconfined compression strength --- Correction of stress reliese and disturbance in unconfined compression tests ---

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Effective stress state of "undisturbed samples" collected from all over japan was investigated aiming at estimating the residual effective stress in the samples after experiencing sampling, trimming and being ready to be subjected to unconfined compression tests. The undrained strength mobilized along the slip circles was theoreticall derived. The average undrained strength along the slip circle being compared with the corrected unconfined compression strength indicated the appropriateness and the limitation of the usage of unconfined compression strength in the stability analysis of soft clay foundations. The backanalysis of 24 case histories of actual failure of soft clay showed a reasonable agreement with the results obtained from the investigation on unconfined compression strength. the conclusions are as follows:1. The effect of sample disturbance and stress release corresponds to within 0.1 in terms of the factor of safety.2. The effect of loading rate in the field corresponds to about 0.2 in terms of the factor of safety. This indicates that the selection of construction method and construction sequence is more influencial to the stability of soft foundations rather than the degree of sample disturbance is.3. The correction factor to be multiplied with the experimentally obtained unconfined compression strength in analysing the stability of soft clays is derived as a function of the plasticity index.