Migration and Deposition Characteristics of Particles in Sand Layers with Fluctuating Water Levels

摘要

Under the influence of large water conservancy projects and seasonal precipitation, the groundwater levels along rivers and lakes show cyclic patterns of change. Thus, the fluctuation in water level is an important factor affecting the particle migration and deposition characteristics in the sand layers considered in projects such as groundwater recharge projects. Existing theories all treat the recharge aquifer as saturated, making it difficult to elucidate the mechanism of groundwater source heat pump recharge blockage in river and lake coastal areas. An extensive laboratory study was conducted here to assess the effect of water level changes on the deposition characteristics of particle migration in porous media. A one-dimensional sand layer migration-deposition test system was used to test particle transport and deposition characteristics at different water levels. The tests were carried out for two combinations of particle sizes at four water levels (110 mm, 220 mm, 330 mm, and 440 mm) and three seepage velocities (0.024 cm/s, 0.047 cm/s, and 0.071 cm/s). The results show that when the seepage velocity is kept constant and the water level is low, the particles flow through fewer pore channels, and as the water level increases, the particle flow through pore channels increases accordingly, so the particles are more easily deposited in the pore channels. This is ultimately reflected in the decrease in the peak relative concentration C/C-0 and the increase in the pore volume ratio P-v. When the water level remains constant, the hydrodynamic effect gradually becomes stronger as the seepage velocity increases, and the originally deposited particles may break away from the surface of the deposit and flow out with the water, resulting in a higher suspended particle concentration of the effluent and a higher C/C-0. Smaller particles are more affected by the hydrodynamic effect than larger particles.