Strength improvement characteristic of cement-solidified dredged marine clay with relation to water-cement ratio

Abstract

Dredged marine sediments were retrieved from a maintenance dredge site for examination on the solidification efficacy. The high plasticity clay (CH) sample had low shear strength and high compressibility, making it unacceptable as a geomaterial for construction purposes. Due to its poor engineering properties, the material was destined for disposal offshore: incurring cost, time as well as contamination risks along the transportation route. With solidification, the soil could be improved for potential reuse in reclamation works, for instance. The laboratory investigation involved admixing ordinary Portland cement with the soil at different water-cement (WC) ratios, ranging from 1.5 to 3.5. Left to mature in a confined, damp environment for periods up to 56 days, the solidified specimens were subjected to the unconfined compression test. The measurements were conducted at predetermined intervals of 3, 7, 14, 28 and 56 days. Duplicate specimens were tested using the unconfined compression apparatus in accordance with BS1377 (1990). The unconfined compressive strength (qu) and Young's modulus (EP) were derived from the stress-strain plots. Both the strength and stiffness were found to increase with lower WC ratio and prolonged maturing, where the solidified soil transformed from a soft, weak material to that of a hard, strong one. The strength improvement was as high as 2.5 times that of the 3-day old specimens, while the stiffness increased by 4 times for the large strain range, as derived from the compression tests. Expediency of solidifying the soil with cement was further examined by correlating the strength, stiffness and deformation with WC as well as rest period.