Sediment hardness as assessed by the vane shear strength.

<p>(A) High-resolution vane shear testing system in the laboratory. Sediments with prescribed sediment relative densities <i>D</i>_r were formed in an acrylic cylindrical chamber set in a larger water tank. Suctions <i>s</i> at the level of the sediment surface were varied by changing the water level in the tank. The vane shear testing was performed by inserting and rotating the vane blade in the uppermost layer of the given sediment. (B) Results of the vane shear testing. The peak value of the measured vane shear stresses represents the vane shear strength τ*, namely the sediment hardness. (C) Field vane shear testing apparatus for surficial sediments. The apparatus directly measures τ*. (D) Sediment hardnesses simulated in the laboratory as functions of suctions and sediment relative densities of the intertidal sediments taken at the Nojima tidal flat. Data in (D) were obtained using both apparatuses shown in (A) and (C) and represent mean values ± SE.