Abstract: A series of direct shear experiments was performed to investigate the influences of pore fluid concentration on the liquid limit, plastic index and shear strength of remolded silty clay. The experimental results indicate that the liquid limit decreases with the increase of pore solution concentration, and the plastic index is similar to that of silt. It is found that the variation of the shear strength with the concentration depends upon the vertical stress applied. For a low vertical stress, the shear strength decreases slightly as the concentration increases; for a medium vertical stress, the shear strength first decreases and then increases as the concentration increases; for a high vertical stress, however, the strength constantly increases as the concentration increases. In addition, the internal friction angle increases with the pore fluid concentration and approaches toward a stable value, while the cohesion decreases rapidly in the early stage, and gradually increases again, remaining at a negative values all the time. These features of the soil behavior can be attributed to the combing effect of electric diffuse double layers, the intergranular stress variation and the void ratio change under coupled chemical and mechanical interactions. Based on the Terzaghi's effective stress principle, the shear strength parameters of the tested saturated silty clay are analyzed, suggesting that the osmotic pressure plays an important role in the occurrence of the negative cohesion of clayey soils.

Key words: chemical action of water-soil, silty clay, consistency limits test, direct shear test, osmotic pressure