Multichannel optical sensor to quantify particle stability under seepage flow

International audienceAn optical sensor was designed to measure the fine solid particles concentration contained in a fluid flow. Thissensor is composed of four light-emitting diodes and four associated light-dependent resistors, allowing the measurement offluid transparency. Given the small device dimensions, it can be placed close to the particles exit from the specimen. Theoptical sensor is able to instantaneously measure a large range of clay or silt concentrations in the effluent, without a significantinfluence of flow rate. The presence of sand grains in fluid flow can be detected. The use of this sensor with a specifictriaxial device allows precise characterization of the initiation and development of the suffusion process on clayey sandspecimens. It is shown that suffusion of clay particles induces a decrease of hydraulic conductivity, which is due to a diffuseprocess of eroded particles filtration. Clay suffusion and filtration processes are influenced by grain-size distribution andalso by grain shape of the coarse fraction. Under a high hydraulic gradient, clay suffusion can be accompanied by sand erosion.The critical value of mean pore velocity to initiate clay suffusion was determined for the types of soils