A new nonlinear seepage model for clay soil considering the initial hydraulic gradient of microscopic seepage channels

There is a clear nonlinear characteristic of the seepage velocity of clay; however, its existing prediction models are mostly empirical, and the prediction accuracy needs to be improved. In this paper, the soil–water retention curve is considered an indirect indicator reflecting the scale distribution of the soil seepage channel to calculate the initial hydraulic gradient of the microscopic seepage channel, based on which a nonlinear seepage velocity prediction model for clay soils was established in combination with the Tao-Kong model. To verify this model, the saturated seepage velocity of three dry densities of Hunan clay under different hydraulic gradients was measured with a GDS permeameter. Using the new model, the saturated seepage velocity under different hydraulic gradients was predicted and compared with experimental results and prediction results from existing models. The comparison showed that the new model has the highest accuracy. Both the prediction and experimental results showed that seepage in Hunan clay exhibits a nonlinear behavior and has an initial hydraulic gradient. When the seepage pressure is small, the permeability coefficient is small; as the seepage pressure increases, there is a steep increase in stair, and the larger the dry density is, the larger the initial hydraulic gradient.