Morphological Evolution of Clay/Sand Mixture Focusing on Clay Loss

Abstract

This study presents the characteristics of morphological evolution of clay/sand mixture and pure sand focusing on the clay loss on the surface layers under regular wave conditions. Hydraulic experiments were carried out using two-dimensional wave flume. Two different wave heights, 0.04 m and 0.07 m, with a wave period of 1.0 s were adopted. The movable beds consisted of silica sand (d₅₀ = 0.439 mm) and kaolin (d₅₀ = 8.0 µm) with the three different clay fractions, 0.0, 0.05 and 0.20. Regular waves were generated for more than 40 hours. Initial and final topography were measured with laser displacement meter and topographic change during experiments was estimated using the video taken with the camera on the side of the wave flume by means of image processing. In each case, the sediments were collected at the locations where the noticeable topographic changes occurred, and the change in clay fractions was examined. As a result, the higher the clay fraction, the smaller the initial topographic change. Over time, however, the similar morphological evolution of pure sand, such as sand ripples, was observed in the clay/sand mixture. The layer separation near the surface due to clay loss contributes to making the sand easier to move, thus separating surface layers into the clay-free layer (sand layer) over time implies an important factor in evaluating mixed soil transport.