Improvement of shear strength characteristics of İzmir Bay’s dredged soil

Abstract

In the last decades, Izmir Bay is negatively affected both environmentally and commercially due to the alluvial deposits carried by Gediz River and other rivers around. To find a solution to this problem, “Izmir Bay and Port Rehabilitation Project” was conducted. After the dredging process, approximately 22 million m3 of dredged soil was unearthed in and around the bay. The dredged soil comprises organic matter; thus, it has a problematic internal structure which has many uncertainties. Therefore, the engineering properties must be comprehensively clarified. In this study, the geotechnical properties of the dredged soil with different organic matter contents (0, 4, 7, and 11% OM) were investigated, and the shear strength behavior was examined with the direct shear test. First, shear strength characteristics of natural dredged material were defined and then, it was aimed to improve the shear strength properties with lime (L), silica fume (S), and thermal power plant fly ash (T). To define the internal structure of dredged soils with different organic matter contents, SEM, FTIR, and XRD analyses were conducted. The specific gravities ranged from 2.52 to 2.76, and the liquid limits ranged between 32.6 and 39.5. The plastic limit values are between 26.4 and 31.0. The plasticity of the dredged soil showed a proportional increase as the percentage of organic matter increased. The internal friction angles of dredged materials were ranged between 34 and 40°. Stabilization process positively affected the internal friction angle with all additive materials. Although lime-added samples have higher internal friction angle values for 20% additive content, silica fume and thermal power plant fly ash–added samples have higher internal friction angle values for 10% additive content.