Evaluation of strength-deformation behavior of clay ground based on the unconfined compression test with suction measurement and triaxial compression test with shear modulus measurement by bender element.

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1. Estimation of in-situ undrained strength based on the unconfined compression tests with suction measurement. Based on a series of test simulating the process from sampling to unconfined and triaxial compression test for saturated clay, the head investigator formerly found that the undrained strength Cu normalized by residual effective stress siguma' versus quasi-overconsolidation ratio QCR( = siguma^1 * siguma^1_5) relationship is represented by a straight line in logarithmic plot, where a', is calculated from measured suction value before unconfined compression test and siguma * is in-situ effective overburden pressure. By using the relationship, in situ undrained strength of clays can be predicted from the results of conventional unconfined compression test with suction measurement. In this study, the examination and confirmation of the validity of the proposed method was performed by comparing the distributions of undrained strength obtained by the method along the depth with those obtained by in situ sounding test results.2. Estimation of in-situ stress-deformation characteristics of clayey soilsBased on the test results by consolidometer and triaxial apparatus, both are equipped with bender element, it was found that modulus of rigidity (G)obtained by shear wave velocity with bender element well coincides with the ones calculated by using the modulus of elasticity (E ) obtained by monotonic and cyclic loaded undrained triaxial tests. It was also found that the modulus G decreases with sample disturbance and its value depends on the magnitude of residual effective stress.It was confirmed by two series of test results mentioned above that the strength-deformation characteristics of clayey soils in-situ can be estimated if the residual effective stress of the specimen can be suitably evaluated.