CYCLIC CHARACTERIZATION OF LIQUEFIABLE SANDS

The method for cyclic characterization of liquefiable sands, which employs the concept of dynamic backbone curve in conjunction with the Masing criteria for construction of unloading and reloading branches of cyclic loops, is refined and verified. The method also encompasses subsequent cyclic loading, when soil undergoes significant degradation due to pore-water pressure buildup. To accurately describe the initial backbone curve and associated initial cyclic loop, and subsequent degraded backbone curves and associated subsequent cyclic stress-strain loops, a well-known hyperbolic model and a degradation model arc modified. Although relatively simple, such modifications enable accurate description of the stress-strain loops of the first and subsequent cycles, even in cases when soil rapidly degrades and liquefies in just a few cycles. Consequently, a much better agreement between the measured and calculated damping values can be also obtained. The investigation is based on test results obtained on five different sands, which either liquefied during past earthquakes or are located in potentially liquefiable zones. The results presented are important for improvement of the nonlinear seismic response analyses of liquefiable sites.