For the purpose of sustaining stress and strain uniformity in a clay specimen and controlling arbitrary strain paths, the authors have developed a strain path controlled mini-triaxial testing apparatus, in which a small size specimen (22.5 mm in diameter and 45 mm in height) is used. In this paper, to investigate shear behavior of clay, the authors carried out a series of strain path controlled mini-triaxial tests using remolded kaolin clay. As a result, strain path dependent shear behavior is observed, which is quite different from that of drained or undrained triaxial test. That is, as increasing the strain increment ratio R between axial and volumetric strains, the maximum deviator stress increases while the maximum excess pore pressure decreases, and the effective stress path shifts off the failure line. Furthermore, the strain path dependent shear behavior of remolded clay is discussed, following that it is closely related to strain increment ratio and dilatancy.
The train path controlled test has been developed by Chu and Lo (1991, 1994) to investigate asymptotic behavior of saturated sand. They emphasized the existence of a unique relationship between an asymptotic stress ratio and strain increment ratio in shear behavior of sand. In the strain path controlled test, volume change is directly controlled along the constant strain increment ratio R (= dεv/dεi) which is a increment ratio between volumetric strain εv and axial strain ε1 using digital pressure/volume control device (DPVC). This control system is also used by Uchida and Vaid (1994). They pointed out that volumetric strain distribution in a sand specimen is not uniform in a conventional drained test. The difference between strain path controlled triaxial test and conventional drained or undrained triaxiai test is illustrated in Fig. 1.