Dynamic Properties of Marine Sediments
In the marine environment dynamic stresses can be generated in a variety of ways, for example by water wave motion, earthquake activity, foundation vibrations etc., and once translated to the seafloor, transmission of the stress wave is dependent on the dynamic properties of the sediment itself. An understanding of the response of seafloor sediments to dynamic stresses is essential to several fields of marine investigation — seismic hazard evaluation, radioactive waste disposal, slope stability, foundation investigation — and this can best be achieved by studying the various parameters which control elastic wave propagation in porous media. Such studies have been undertaken at the Marine Science Laboratories where the dynamic elastic parameters and damping characteristics of sediment samples have been obtained via testing in a modified resonant column apparatus. In this device, concurrent acoustic measurements using pulse propagation techniques and continuous sinusoidal wave techniques have allowed the dynamic properties to be obtained over a range of strain levels, strain rates and effective stress conditions. The typical strain amplitudes vary between 0.0001% and 1% with the duration of a single stress reversal ranging from 0.00001 second up to 100 seconds. The results from tests carried out on a range of marine sediment samples have allowed the production of a catalogue of strain level and strain rate correction curves. Thus in situ results from low strain, short duration dynamic loadings, as imposed by a seismo-acoustic pulse, can be corrected via these curves to produce information applicable to dynamic loading under a wide range of strain levels and strain rates.
KeywordsEffective Stress Strain Amplitude Strain Level Shear Wave Velocity Foundation Vibration
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