SALINITY AND MINERALOGY EFFECTS ON SECONDARY CONSOLIDATION BEHAVIOR OF CLAYS

The soft marine clay, deposited under the marine environment in North of Jiangsu plain, is rich of the montmorillonite and saline water. During the post-sedimentary period, the soil suffers the invasion of the surface and underground freshwater, leading to the alteration and reduction of pore water salinity. Presently, the secondary consolidation behavior is generally based on the in-situ soil behavior in a current environment. Hence, this non-consideration on the pore water salinity alteration may result in the insufficient redundancy and potential risk. To clarify the evolution of the soils' secondary consolidation behavior due to the alteration of pore water salinity, the impact of pore water salinity and clay mineral on the soil behavior is necessary to be investigated. To simplify the mineralogy influence, the commercial kaolin and bentonite are selected. The consolidation behavior of artificial clays changing with pore water salinities(NaCl solution) are investigated using oedometer tests. The results showed that the compression index C_c and the primary consolidation process of bentonite-kaolinite mixture decrease with water salinity increasing. At a certain applied stress and void ratio, the secondary consolidation coefficient C_α of montmorillonitic clay also decreases with water salinity increasing. Meanwhile, the ratio of C_α to C_c is not a constant and deviated from empirical data. The main mechanism is that the compression of diffused double layer. However, the water salinity does not significantly influence secondary consolidation behavior of kaolin. Therefore, it is important to take pore water salinity into consideration for secondary consolidation prediction of montmorillonite-rich clays.