Thermal Diffusivity and Strength of Tidal Flat Sediments During a Tidal Simulation

Coastal margins and tidal flat sediment systems are some of the most complex, heterogeneous and energetically dynamic regions on earth. Tidal flats are repositories of terrigenous and biogenous sediments that are shaped by tides, waves and storms and utilized by birds and benthic organisms. They often lie adjacent to rivers that enable inland passage for ships and access to spawning grounds for fish. As such, they are subject to numerous anthropogenic effects, such as fishing, clamming, beach combing, and automobile traffic. Depending on their morphology and tidal range and periodicity, tidal flats are inundated or exposed for variable amounts of time and over widely different areas. To better understand the properties and distribution of the sediments within this setting, an ongoing study is being conducted to determine the relationship between thermal and geotechnical properties of tidal flat sediments. Our specific objectives are: (1) to determine how to assess thermal properties of laboratory-simulated tidal flat sediments and (2) to assess the relationship between sediment composition and undrained shear strength. The ultimate goal of these efforts is to remotely predict tidal flat trafficability (humans or vehicles) from the temperature signature. To understand how mineralogy influences thermal properties of sediments, several sediment types were tested. To simulate the heterogeneity of the tidal flat, a range of sand-clay mixtures was evaluated. The sand-clay percentages in these mixtures ranged from 100:0 to 0:100 with fractional percentages decremented or incremented by 10 or 20 % until all possible sediment mixtures were achieved. Though more complicated scenarios can be simulated, the initial experiments only considered fully saturated sediments. Each sediment tested was exposed to a heat lamp and the resulting temperature gradient was measured every two centimeters with a vertical thermistor array.
Presented at the MTS/IEEE Oceans '09 Conference held in Biloxi, Mississippi on 26-29 October, 2009. Published in the Proceedings of the MTS/IEEE Oceans '09 Conference, 2009. The original document contains color images. All DTIC reproductions will be in black and white.