Detection of slight cementation in offshore carbonate deposits from laboratory testing

摘要

Diagenesis of offshore carbonate soils may lead to precipitation of cement between grains due to abundance of calcite, aragonite and other salts in seawaters. Even slight cementation may significantly modify the engineering behaviour of carbonate soils, both at small and large strain levels. In many foundation problems, it is essential to detect slight cementation, which may exhibit strength response similar to that induced by suction and overconsolidation, particularly in fine grained carbonate soils. This study investigates the behaviour of slightly cemented carbonate soils under both small and large-strain conditions in an attempt to establish the criteria required to detect slight bond in offshore carbonate samples. A laboratory testing program was carried out using a combination of 1-d compression and conventional triaxial testing with measurement of shear wave velocity. Several symptoms have been recognized due to presence of slight cementation. Specifically, bond increases the shear-wave velocity, V_s (or, small-strain stiffness), reduces the dependency of V_s on effective stress, and reduces the coefficient of earth pressure at rest (K_0). A combination of these symptoms along with brittle stress ratio-strain behaviour during K_0 consolidation provides strong evidence of presence of slight cementation.