Application of Asaoka’s Method in Multistage Triaxial Compression Testing of Normally Consolidated Soils

Determination of shear strength parameters becomes a challenge when it is difficult to retrieve a minimum of three identical undisturbed soil specimens. In such a situation, multistage triaxial compression testing can be adopted using a single specimen. Multistage triaxial testing involves stage-wise consolidation and shearing at three confining pressures without the failure of the specimen until the last stage. A critical issue associated with multistage triaxial testing is the estimation of ultimate deviator stress and the corresponding pore pressure as the specimen was not allowed to reach failure in each stage. Conventionally, the failure stress state in each stage is computed by extrapolating the stress–strain and pore pressure–strain data to a finite strain by employing Kondner’s rectangular hyperbola model. However, it is reported in the literature that the aforementioned method often overestimates the deviator stress and pore pressure values. In this context, the present study investigates the suitability of Asaoka’s observational procedure for predicting these values at failure state. The validity of the proposed procedure is verified by comparing the ultimate deviator stress and pore pressure values obtained by analyzing the stress–strain data collected from the literature and by performing multistage triaxial testing on three reconstituted soil samples with that of the rectangular hyperbola method. From the results, it was observed that Asaoka’s method is more suited for predicting the shear strength parameters. It is believed that the proposed methodology would aid in obtaining the shear strength parameters of a soil from a single specimen by conducting multistage triaxial testing.