SEDIMENTATION AND CONSOLIDATION OF A HIGH WATER CONTENT SOIL
摘要
The permanent siltation of harbours and estuaries has led their administrative companies to undertake dredging operations in order to guarantee a minimal water depth required for free access to port infrastructures. This long and expensive work interferes with the port trade. Dredged material is injected into the sea with the creation of a maritime dump or stocked on earth in basins. In each case, there will be a formation of a high water content soil. This paper deals with the geotechnical formation of high water content soils by means of an experimental laboratory sedimentation/consolidation bench. We have devised and realized a controlled bench which allows us to analyze the natural soil formation under self weight. The tested soil settles in sedimentation/consolidation columns (1.5 m. in height, 100 mm in diameter). Pressure and density measurements in the tested soil are possible on the whole height of the vertical column. Values of density are obtained by gamma-densimetry. The precision of the measurements is +/-0.5% for the density and +/-3 Pa for the pressures. Each test is performed over 32 days with 17 intermediate times. An originality of this bench lies in the fact that it allows measurements with a good precision in density and pressure at a very early state of soil formation (first values at 1 .33 min. from the beginning of the test). The test we are presenting concerned the natural mud found in the Loire estuary (France) prepared to an initial concentration of 200 g/ 1 (density 1. 135). These measurements are studied in terms of evolution of total stress, excess pore pressure, void ratio and effective stress as related to time. For this test, we present the density and pressure measured profiles as well as the deduced effective stress curves, paths of particles and rates of consolidation. On a void ratio versus effective stress diagram, we clearly show the evolution of soil consolidating under self weight during the intermediate phase of its formation