MIGRATION OF RECTANGULAR MINING PIT COMPOSED OF UNIFORM SEDIMENTS

Sand and gravel mining from riverbeds is a major supply of construction materials. A mining pit in a riverbed is very unstable and subject to scouring and deposition, which results in migration of the pit. A series of experiments was conducted to investigate the migration behavior of several rectangular pits of different sizes composed of uniform bed material. It was found that the maximum scour depth decreases as sediment transport capacity increases, and that the effective length varies inversely with sediment transport capacity. The migration of the pit can be separated into two periods, a convection period and a diffusion period. The migration speeding each period is constant and increases as sediment transport capacity and effective length increase and vary inversely with the depth of the pit. Regression equations for the maximum scour depth, effective length, shape, and migration speed of the pits were obtained. These equations were then used to predict the size, shape, and speed of a migrating rectangular pit.