Abstract: In current study, a high accuracy small strain triaxial apparatus is developed using linear variable differential transformer (LVDT) sensors. The structure of the triaxial apparatus, the specification of the sensors, and the technical details of the small-strain measurement are introduced in detail. E/P regulators are used to control the axial load and cell pressure. Meanwhile, a motor driven actuator can be used to provide axial load. The apparatus can achieve complex stress path for triaxial tests with controlled stress or strain. Constant temperature, ground connection, and high accuracy DC power to reduce the electrical noise in the signals and to obtain a precise small strain measurement. Median filtering method is applied to increase the accuracy of measured LVDT displacement data. Undrained triaxial shear tests under K0 consolidation are conducted on Shanghai soft clay. The secant modulus of Shanghai soft clay in small strain level (0.001%-0.1%) is obtained. It is confirmed that the developed triaxial apparatus using LVDT displacement sensors can obtain secant modulus in smaller strain better than other existing products.

Key words: triaxial apparatus, small strain, secant modulus, LVDT sensors, Shanghai soft clay