Assessing the efficiency of filters protecting base soil subject to erosion

Dams filters are mainly designed using filter criteria based on the grain size distribution (Sherard & Dunnigan, 1985). This paper reports experimental results obtained on the soil-filter system behaviour subject to different hydraulic and geometrical conditions. A silt soil and three sandy gravels were used as the core and different filters (F1, F2 and F3), respectively. The objective of this study was to determine the effectiveness of the filter to protect the silt submitted to erosion under controlled water flow (horizontal and vertical configurations). Particles transport and filtration through each granular filter were analysed as regards to filter retention capacity, particles size selection and grains shape. This study was achieved by conducting a comparison of the behaviour of the three filters against the silt erosion. A comparison of the efficiency of the filters is assessed toward the required usual relationship criterion and the most appropriate for the dam filters

Contribution for assessing filter efficiency in zoned dams: (Paper and Abstract)

Dam filters are mainly designed using filter criteria based on the grain size distribution. The main design criteria against which performance is assessed are a criterion for retention of fine particles. The characteristic size of finer fraction influences the size distribution of the filter pore and hence the retention capacity of flowing particles, and the permeability of the filter itself. This paper reports experimental results obtained on the soil-filter system behaviour subject to different hydraulic and geometrical conditions. Many core soils and filters were used. The objective of this study was to determine the effectiveness of the filter to protect the silt submitted to erosion under controlled water flow. Particles transport and filtration through each granular filter were analysed as regards to filter retention capacity and particles size selection. The plasticity of base soil influences greatly the filtration since slightly plastic soils are more erodible than plastic soils. The analysis of hydraulic conductivity in the filter is of a great concern and leads to understand the filtration process. A comparison of the efficiency of the filters is assessed toward the usual required criteria and the most appropriate for the dam filters. Matching experimental results with filter design criteria reveals that many of them are conservative. The filter porosity variation was assessed and correlated with clogging particles volume. The evolution of such parameter may be an indicator of likely filter clogging. A new approach of filter clogging was proposed by evaluating a damage index which is affected by various parameters such as the ratio D15/d85 and the size of eroded particles. An approach linking the geometrical parameters (damage index) to the hydraulic conductivity leads to an estimation of the filter performance which provides an interesting and realistic criterion