Dynamic Response of Mercer Slough Peat

The behavior of a peat from Mercer Slough in Bellevue, Wash., was investigated by a program of field and laboratory testing. The peat was very soft, very weak, and highly compressible. Water contents averaged approximately 600% and in situ shear wave velocities were measured at 12–30 m/s. Cyclic triaxial and resonant column testing indicated that the modulus reduction and damping behavior of Mercer Slough peat was significantly influenced by strain amplitude and effective confining pressure and was weakly influenced by loading frequency and overconsolidation ratio. Comparison of the behavior of Mercer Slough peat with other highly organic soils suggests a trend of increasing linearity and decreasing damping with increasing effective confining pressure. Site response analyses indicated strong response at low frequencies with spectral shapes that differ significantly from the standard shapes implied by current codes.