Role of suction dynamics in evolution of intertidal sandy flats: Field evidence, experiments, and theoretical model

摘要

In this paper we present and discuss the role of the dynamics of suction, that is, negative pore water pressure relative to atmospheric air pressure, in the evolution of intertidal sandy flats. This is done through the combined use of field evidence, laboratory experiments, and a theoretical model. Field observations were performed in the estuary of Obitsu River located in the east coast of Tokyo Bay, Japan. Laboratory experiments were performed in a calibration chamber as well as in a laterally scaled model flat subjected to water/groundwater level variations. The present study demonstrates that the suction dynamics associated with the tide-induced groundwater level variations play a substantial role in the temporospatial evolutions of voids, stiffness, and surface shear strength in cyclically exposed and submerged soil. The suction-induced void state changes are a consequence of cyclic elastoplastic contraction of the soil and are accompanied by distinct morphological changes, despite the lack of significant surface shear stresses acting on the soil. Such soil behavior occurs in regions where suction develops above the groundwater level during low tides and strongly depends on the way in which such suction develops. Discussions are made on how these suction dynamics effects could contribute, via feedback involved in surface transport processes, to the overall morphological evolution of cross-shore intertidal flat soils.