Deformation modulus of reconstituted and naturally sedimented clays

The undrained secant deformation modulus Eu is an important parameter to quantitatively estimate the undrained settlement of soft clays. A series of isotropically consolidated undrained triaxial compression shear tests were carried out on four reconstituted clays and two naturally sedimented clays to evaluate the effects of the initial water content w0, liquid limit wL, and soil structure on Eu. The test results showed that the variation in Eu with deviator stress was significantly affected by w0 and wL for reconstituted clays. The normalized modulus Eu/(p′)0.9 linearly decreased with increasing w0/wL. This linear relation at a lower wL lies above that at a higher wL. These observations suggest that the soil with lower plasticity and lower initial water content possessed higher values of Eu. As the deviator stress increased, the effect of w0 and wL on Eu gradually vanished. It is also evidenced that the value of Eu for naturally sedimented clays depended on the soil structure. The soil structure clearly enhanced the Eu in the preyield regime in comparison with the corresponding reconstituted clay. Once the soil structure was damaged with increasing consolidation stress in the postyield regime, a significant reduction in Eu was observed with a lower value than that of reconstituted clays. The difference in Eu/Su between naturally sedimented and reconstituted clays gradually decreased with increasing deviator stress. This implies that the effect of the soil structure on Eu diminished at higher deviator stress levels. •The variation of undrained modulus Eu with initial water content is proposed.•The normalized modulus Eu/(p')0.9 is linearly correlated to w0/wL.•The degradation of Eu for natural clay due to loss of soil structure is observed.•The influence of soil structure on Eu vanishes at higher deviator stress level.