THE STUDY OF SAND CAPPING METHOD BY SAND-UPWELLING SYSTEM

Abstract

A sand-upwelling system as a new sand capping method was developed to create a clean bottom environment in lakes and semi-enclosed water area.
This system is mainly comprised of a water jet pipe to well up clean sand from a sand stratum, which possibly lies below contaminated bottom sludge. Because of the principle of this system, sludge disposal and clean sand procurement are unnecessary, which are inevitable for a conventional dredging system. In addition, the low turbidity by this system during operations may hardly affect ecosystem in water area. A scale model test in the laboratory and field tests at Lake Suwa and Lake Sinji proved that the sand capping was completely implemented and the turbidity range was quite low by the new system. The field observation in lakes also demonstrated many Limnodius and Shellfishes appeared in the sand capping area. In order to plan implementation of sand capping with precision, several parameters, which control up-welling sand flux, were found in hydraulic model tests and equations to estimate sand flux rate were established. Numerical simulation with the Lagrangian model of solid-liquid two phase flow (MPS method) was carried out even for the initial stage of up-welling to represent the phenomena from the hydrodynamic viewpoint. The simulation results were good in agreement with the phenomenon observed by the model tests.