The effect of initial concentration on the consolidation behaviour of mud

Abstract

Land reclamations in deltaric areas provide space to meet the demand for a safe place to live and work. Sand, a traditional filling material in some locations is becoming scarcer. An alternative filling material is mud. Mud consists of clay, silt, sand, organic material, water and gas. Therefore, it is a versatile material and difficult to predict its consolidation behaviour. This research will contribute to better predicting the consolidation of soft cohesive sediment. The objective of this research is to determine if the consolidation behaviour is a function of the initial conditions. To assess the effect of the initial concentration of mud on consolidation behaviour, settling column experiments and Seepage Induced Consolidation (SIC) tests were performed. These experimental methods determine two sets of material parameters for consolidated beds with varying initial concentration. The first method is used to determine material parameters for a low initial concentration suspension, the second method for a high initial concentration mud mixture, when particles are no longer in suspension. The most important parameters in consolidation are permeability and effective stress. The consolidation behaviour is simulated with a 1-DV model that solves the Gibson consolidation equation. To simulate the consolidation behaviour of a high concentration a swelling coefficient is added. The density profile of a consolidated bed is simulated with material parameters from both experimental methods. Material parameters obtained from these methods differ by an order of magnitude. The simulated density profile with material parameters obtained from a SIC test compare better to the measured density profile from a physical model. When the density profile of a column is simulated with varying material parameters from SIC tests, there is an effect of material parameters on the simulated density profile. The simulated density profiles compared to measured density profiles show that the swelling is only present in high concentration mud. Therefore, the consolidation behaviour is dependent on the initial concentration. The material parameters obtained for low and high initial concentration mud are different. Thus, the initial concentration has an effect on the material parameters. There are differences observed between density profile simulations with varying material parameters. Therefore, the material parameters have effect on the final conditions. However, the significance of this effect is unknown. This research contributes to a better understanding of how to predict consolidation behaviour of mud or soft cohesive sediment.