Investigation of engineering characteristics of calcareous soils from fringing reef

Engineering characteristics of calcareous soils are more peculiar due to the grain geometries, hardness and intraparticle voids. In the fringing reef in Sanya, calcareous soils were mixed with some terrestrial deposits, such as quartz sand and clay. In this paper, a series of laboratory and in-situ tests are conducted on calcareous soils to investigate the engineering characteristics and the effect of water saturation: laboratory large-scale direct shear tests, large-scale oedometer tests, X-Ray diffraction experiments, in-situ Plate Load Tests (PLTs) and Dynamic Cone Penetration Tests (DCPTs). The results showed that: (i) apparent cohesion of calcareous soils is quite higher than that of quartz sand but decreases significantly due to the softening effect of water; (ii) the bearing capacity decreases by 43% and deformation modulus decreases by 31% at the presence of 20% clay minerals; (iii) deformation modulus reduces 80% in saturated condition compared to dry condition; (iv) the relationship between N-63.5 and bearing capacity of calcareous soils was established; therefore, engineers can decrease the amount of PLTs and increase DCPTs in the site exploration of fringing coral reef according to the testing results.