Forming a thin sand seam on a clay slurry with the aid of a jute geotextile

Abstract

In the layered clay-sand scheme of land reclamation, thin horizontal sand layers are sandwiched between hydraulically placed marine clay to provide a shorter drainage path for the consolidation of the clay. The process of forming a thin sand seam on top of very soft clay slurry at water contents of 200-300% is critical to the success of the scheme. This process is dependent upon the intensity of sand spread, the water depth for sand spreading, the grain size of sand used, as well as the slurry strength. Experiments in 150 mm cylindrical columns and in the field demonstrate that substantial sand losses through penetration into the clay are inevitable for slurry above 200% water content. However, with the aid of a low-cost and low-density type jute geotextile laid on the slurry surface, the sand seam can easily be formed by careful thin layer sand spreading through water onto the jute blanket lying on the slurry surface. The jute-slurry interface friction can be measured by a simple jute sheet vertical penetration test into slurries of various water contents. Model bearing capacity tests on a rectangular loaded area of a 500 g/m2 jute geotextile suggest that bearing capacity factors of jute on clay slurry is about 5-6·5 times the jute-slurry interface friction for slurry water contents of 150-300%. Clay slurry from 250 to 500% water contents in cylindrical columns of 150, 200 and 250 mm diameters with jute geotextile surface layers were carefully subjected to thin sand spreading to failure. Taking into account wall friction and buoyancy effects, it is found that the thickness of sand formed prior to failure can be reasonably estimated from the measured jute-slurry interface friction and the bearing factors of clay slurry reinforced with a jute geotextile layer. Thus, the use of a low-cost jute geotextile allows for the expedient means of forming a sand seam on top of very soft clay slurry with minimal sand losses. © 1994.