Influences of seepage of muddy water on the permeability of coarse-grained soil

Coarse-grained soil has widely been used for construction and geological bodies, such as hydraulics and civil engineering. It is critical to clarify the transformation under the impact of muddy water seepage for better engineering uses. In this study, a series of calculation formulas were derived for the seepage of coarse-grained soil in a circular tube under the action of muddy water. An apparatus of muddy water seepage was self-developed to systematically investigate the characteristics of seepage in the coarse-grained soil subjected to the muddy water. A comparison was also carried out to verify the variable equations of soil hydraulic gradient, permeability coefficient, seepage flow, and the filling rate of pores. In addition, a calculation formula was deduced to determine the effect of muddy water seepage in the circular pipe on the differential equation of the permeability and the permeability coefficient of the coarse-grained soil at each stage after the experiments. The results are as follows. The seepage process of muddy water in the coarse-grained soil was generally divided into three stages: the smooth migration stage of fine particles (Stage 1), the coexistence of pore blockage and migration (Stage 2), and the deposition on the top of the coarse-grained soil (Stage 3). There was a significant correlation among the concentration of muddy water, the water head on the hydraulic gradient, and the permeability coefficient of coarse-grained soil. Specifically, there was also a strong intensity in the migration of fine particles, clogging, and deposition with the increase of muddy water concentration and water head. Furthermore, the hydraulic gradient inside the soil column increased significantly, as the permeability coefficient gradually decreased. It was very likely to occur the blockage and siltation, due mainly to the greater inhomogeneity coefficient of the coarse-grained soil, and the less smooth channel available for the fine particles to migrate, particularly under the smaller internal porosity and the lower connectivity. As such, the overall lower permeability was obtained in the coarse-grained soil during this time. Alternatively, the water head greatly contributed to the early migration of fine particles. But, the water head resulted in a higher speed of internal obstruction and top deposition at the same time. More importantly, the distance was also reduced for the movement of fine particles downward, leading to the dramatically dropping rate of permeability coefficient. The reason was that the fine particles migrated downward over a short distance during the process. Additionally, an unfriendly surrounding occurred under the rise of the concentration, leading to less movement of minute particles. The atmosphere was also produced for the less friendly environment in the period of the particle movement. It infers that most pores in the coarse-grained soil were filled with the water to steadily diminish the room in the direction of a seepage channel. The steepest drop gradient was found between 0 and 5 cm, and then more gradually flattened out between 5 and 20 cm at the stages. Consequently, the movement rate of particles increased on the top layer of coarse-grained soil. The finding can offer the theoretical basis for engineering applications and the seepage of muddy water. In particular, the anti-seepage properties of coarse-grained soil can be subjected to the change under the impact of muddy water seepage.