Step Loading Compression of Ultra-Soft Soil under Radial Drainage Conditions

Abstract

Step loading compression measurements of ultra-soft soil, obtained from marine environment, were carried out with a hydraulic consolidation cell at the moisture contents of 150 and 168%. Three different drainage conditions were tested: radial outward, inward, and both inward and outward drainages. Ultra-soft soil showed a significant settlement in the first step of loading. There was little pore pressure dissipation, which implies little effective stress gain and with large magnitude of settlement in low stress range. New compression parameters , , and are proposed for viscous and intrinsic states inclusive of low stress log cycles. A correlation between void ratio at 10 kPa effective stress () and void ratio at liquid limit eL was proposed and the relevant compression parameters were predicted. The magnitudes of settlements at various loadings were subsequently predicted using the proposed basic equations and were found to agree well with the measured data. Dimensionless time factor curves for various radial drainage conditions were also proposed. By utilizing these curves, time rate of settlement was predicted, which indicated a good agreement between predicted and measured rates of settlement. It was furthermore found that the predicted time rate of settlement could be ascertained using the coefficient of large strain consolidation estimated from void ratio versus hydraulic conductivity relationships. This research will make a contribution in the field of geotechnical engineering as it seeks to improve fundamental understanding of the compressibility of ultra-soft soil from marine environment, by means of step loading compression measurements with a hydraulic consolidation cell.