Geo-parametric study of dredged marine clay with solidification for potential reuse as good engineering soil

Dredging is an essential process in the development, expansion and maintenance of ports, jetties and various water bodies. The process of removing sediments to create or maintain certain water depths inevitably produces large amounts of dredge materials. These displaced materials are generally soils of fine-grained nature, i.e., clay and silt size particles with limited usability due to low strengths and high compressibility. Besides, exposure of the sediments to contamination via the waterways has made disposal of the material a much more regulated and often costly practise, with uncertain risks of future detrimental effects to the dump site's surrounding environment. It is therefore favourable to explore the reusability of the dredged soils to minimise the need dumping. The present study examines the reuse potential of a dredged marine clay sample treated with induced solidification using binders like cement and coal ash. A series of geo-parametric measurements were performed on the material, including the physical and chemical properties as well as the relevant mechanical responses, i.e., strength and compressibility. The dredged sample was prepared in dry powder form and remoulded with an optimum water content to produce the base soil for solidification. This was necessary to ensure consistency of the water content in the soil for the various batches of specimens prepared for the different tests. It was found that the fundamental characteristics of the material could be effectively improved with the addition of small dosages of binders, as demonstrated by the filling of voids and aggregates formation in the solidified soil. The mechanical properties were also found to improve with prolonged rest period, where over 100 % strength increment and 60 % compressibility reduction were observed after 28 days. Binder-wise, the coal ash was less potent when used on its own and appeared to require activation by the cement for solidification to take place. Indeed, the blend of (3 % cement + 7 % fly ash) and (5 % cement + 5 % fly ash) produced the most significant strength and compressibility improvement, respectively. In short, corresponding results from the various tests conducted provided a better understanding of the solidification mechanism in the dredged marine clay sample for potential implementation on site.