Estimation of shear moduli and damping factors of earth dam materials

Abdel-Ghaffar and Scott developed a procedure for extracting the shear moduli and damping factors of soils based upon strong motion records from earth dams. It is a very efficient procedure for earth dams that exhibited predominantly first mode response along the upstream-downstream direction. In their approach, they employed digital band-pass filters on the crest and abutment acceleration records, and constructed the hysteresis loops of soils by treating these filtered records as the input-output to a non-linear SDOF structure. In the process an important superposition assumption was implicitly introduced. This study looked into the implications of this linear superposition assumption on presumed nonlinear systems. Specifically, numerical simulations were conducted in finding out whether or not such a procedure is capable of extracting a known input dynamic behaviour of soils. It was found that the hysteresis loops were generally distorted, and to minimize errors only those loops of larger strain amplitudes should be used. Simple guidelines were suggested accordingly. Applications to real records from two dams were carried out following the proposed guidelines. Results of such applications were explored.