Stress-Ratio-Based Interpretation of Modulus Reduction and Damping Curves

Abstract

Modulus reduction and damping values are commonly plotted against cyclic shear strain amplitude (γc), and the resulting curves are known to depend on mean effective stress (p′), plasticity characteristics, strain rate, and number of loading cycles. The dependence on p′ is potentially problematic for undrained effective stress analysis where excess pore pressure may develop during loading. This paper presents a new concept in which normalized modulus reduction (G/Gmax) and damping (D) values are plotted against stress ratio (η) rather than γc. Relations developed for sand, clay, and peat are found to be essentially pressure-independent when G/Gmax and D−Dmin are plotted versus η,whereas all three are pressure-dependent when plotted versus γc. This finding is potentially useful for undrained effective stress analysis where p′ may change during loading, and provides a new approach for interpreting laboratory tests in future development of G/Gmax and D curves.