Abstract: Due to the effect of sorting by hydraulic dredger fill, the foundation of dredged coral reef in the South China Sea contains fine calcareous silt interlayer with uneven thickness. Compared with coarse-grained calcareous sand, calcareous silt presents higher compressibility, lower bearing capacity and larger settlement deformation, which adversely affect the safety of buildings on coral reefs. In this paper, the characteristics of primary and secondary consolidation settlement, consolidation time and consolidation rate of calcareous silt were obtained through laboratory consolidation tests, for better understanding the engineering properties of calcareous silt and calculation of coral reef foundation settlement. The calcareous silt shows 0.03?0.37 MPa?1 of the compression coefficient and 6.67?54.79 MPa of the compression modulus. Compression coefficient is directly proportional to moisture content and inversely proportional to dry density. Compression coefficient lower than 0.1 MPa?1 and compression modulus more than 20.0 MPa occurs in moderately dense and dense calcareous silt with water content of less than 15% as low compressibility soil, but loose calcareous silt is moderately compressible. Compared with quartz sand under the same dry densities and moisture contents, the compression coefficient of quartz sand is higher than that of calcareous silt, while the compression modulus is lower than that of calcareous silt. Under the same dry density and water content, both Hangzhou Bay silt and calcareous silt show moderate compressibility. However, the compressive modulus of calcareous silt is slightly larger than that of Hangzhou Bay silt, and its compressive coefficient is slightly smaller. When the load exceeds 200 kPa, the degree of consolidation of calcareous silt reaches 0.95 in the first 5 hours of the consolidation test. Therefore, it suggests 24 hours for the consolidation time of calcareous silt under loading less than 200 kPa but 5 hours under loading greater than 200 kPa for the testing efficiency.

Key words: calcareous silt, dry density, moisture content, compressibility index, rate of consolidation