Small Scale Physical Model for Studying the Effect of Rock Mass Parameters in the Hydraulic Erosion Process of Unlined Spillways

Physical flow models are used to study parameters affecting the erodibility of rock in dam unlined spillways. Among the existing physical models, the parameters of joint orientation and of protrusion are the most studied. However, other rock mass parameters have an important contribution in the erosion mechanism but they were given less attention in existing research or, when studied, mixed results were obtained. In addition, the majority of models simulate rock mass considering a single block, which cannot simulate possible interactions between blocks. To address this problem, a scale model that simulates an existing spillway was built in a UQAC laboratory. This model is a 1:40 scale of the existing spillway. The model is equipped with a pump allowing a constant flow at velocities between 3 m/s and 5 m/s which allows reaching flow rates between 290 L/s and 460 L/s. The water flows along a 9° inclined channel design to insert concrete blocks that are placed in a manner that represent the fractured rock mass. The blocks are instrumented with pressure sensors to measure the pressure applied to each of their faces. The model is also equipped with cameras to observe the behaviour of the blocks subjected to the water pressure. The physical model makes it possible to vary several rock mass and hydraulic parameters, such as joint orientation, joint opening, protrusion, block volume and shape, joint roughness, flow rate and velocity, as well as channel roughness to evaluate their impact in the rock erosion process.