Abstract: Pore solutions play an important role in the shear strength of soils. A series of shearing and microcosmic tests are performed on the samples saturated with NaCl solutions with different concentrations to investigate the effects of pore solution concentrations on the effective strength of clay. The experimental results show that the pore solution concentrations have strong effects on cohesion of samples. The cohesion decreases with the increase of pore solution concentrations. As the concentration approaches 0.1 mol/L, the cohesion decreases to below 0 kPa. The cohesion depends on the block effect of physical and chemical forces between particles on the interparticle sliding. The repulsion decreases with the increase of the pore solution concentration which makes the interparticle sliding more easily. Due to the development of real pore pressure in the samples, the cohesion decreases to below 0 kPa. The environmental scanning electron microscopy tests on the microstructures confirm that clays form flocculation in NaCl solution and form aggregation in water.