ABSTRACT

Clay content plays an important role in wave-seabed interaction. However most of the studies so far concentrated on the sandy or silty seabed. In this study, laboratory experiments were carried out to investigate the impact of clay content on the dynamic behavior of the clay-sand seabed under wave actions with changing of wave heights as well as the concentration of clay in the mixed bed. The pore water pressure and the wave height were measured and analyzed. Results showed that clay content significantly affected the wave pressure on the seabed surface and accumulation of pore water pressure inside the bed.

INTRODUCTION

The interaction between waves and seabed soils has been considered as an important field of coastal engineering. Wave induced liquefaction of seabed soils may reduce the effective stress between the individual grains and will cause the damage to structures located on the seabed (Kirca et al., 2014). There are two main mechanisms of seabed liquefaction under waves: residual vs. momentary liquefaction. Residual liquefaction is associated with the accumulated pore-water pressure gradient, whereas the momentary liquefaction is associated with the amplitude of pressure oscillations (Sumer, 2014). Therefore, many research efforts have been put on the wave-seabed interaction in the last few decades. For most of the coastal zones, seabed soils are generally classified into three categories, i.e., sand, silt and clay. In the past 30–40 years, the process leading to the wave induced liquefaction has been extensively investigated and different factors affecting this process were studied on non-cohesive sand and silt seabed (Seed and Rahman, 1978, Barends and Calle, 1985, Sumer and Fredsoe, 2002, Tzang and Ou, 2006, Sumer et al., 2006). While, a few have been carried out on wave induced clayey soils because of the widely accepted supposition that clayey soils are in general non liquefiable.

However, the phenomenon of liquefaction of clayey soils has really been observed during an earthquake (Ishihara et al., 1989, Miura et al., 1995, Perlea et al., 1999). Therefore, some researchers have studied and evaluated the behavior of clayey soils during the earthquake. The effects of several factors on the seismic-induced liquefaction of clayey soils, such as cyclic shear stress and frequency (Ansal and Erken, 1989, Zergoun and Vaid, 1994), initial static shear stress (Lefebvre and Pfendler, 1996), and the over-consolidation ratio (Azzouz et al., 1989) have been relatively well-studied. More recently, Gratchev et al. (2006) investigated the mechanism of liquefaction of soils with different clay contents at the microscopic level, as well as the influence of clay content and soil plasticity on the clayey soils. It was pointed out that the liquefaction potential of soil was strongly related to specific particle arrangements, and the open microfabric in which clay aggregations at the sand particle contact points is vulnerable to liquefaction. Moreover, it was found that the presence of a small amount of bentonite (<7%) could cause rapid liquefaction, while a further increase in bentonite content (>11%) lead to the opposite effect of raising soil resistance to liquefaction.

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