AN EXPERIMENTAL STUDY OF SAND CAPPING IN LAND RECLAMATION

Abstract

In land reclamation projects and slurry waste disposal schemes in which large quantities of clay slurry are involved, sand capping is an economical method of treating the slurry. When the sand is spread on the clay slurry during the initial spreads, the sand particles will penetrate into the slurry. Some of the problems associated with the sand penetration in clay slurry are studied in this thesis. One of the important parameters governing sand penetration is the shear strength of the clay slurry. The measurement of shear strength of the clay slurry is limited to only a few methods. An extensive investigation shows that the thin plate penetration method is most suitable for such work. An in-depth investigation was conducted on this method and results show that it is simple, quick and reliable. Using the thin plate and the Swedish fall cane, shear strengths of different types of clay, mixed with different amounts of sand and at varying water contents, were determined. Analysis of the results shows that at high water contents, the relationship between the water content and the logarithm of shear strength is essentially linear. When the water content is greater than twice the liquid limit, plotting the shear strength against the ratio of water content to liquid limit gives a good fit for all the samples tested. A significant increase in the shear strength of clay slurry is observed when the amount of sand added has a void ratio greater than 5 (treating the clay slurry as the permeating fluid). Results of sand penetration studies show that the sand penetration is governed by the shear strength of the clay slurry and the rate of sand accumulation, rL, at the slurry surface. For the penetrated sand, the ability of the slurry to trap sand particles depends on its shear strength and the value of parameter rM, which incorporates the momentum of sand particles. When sand particles impinge on the submerged clay surface, the dynamic force is found to be negligible. A semi-empirical model on the mechanics of sand settling in water is proposed and it is able to evaluate both parameters, rL and rM. Another model is proposed in the sand penetration study to predict the conditions underwhich penetration will occur.