Normally, a sandpack is prepared from sorted sand with a known mesh size and a porosity value. The mesh size can be converted to average or nominal particle diameter. My concern is to determine nominal or average pore and channel size for such a sandpack.
Well,
The term uniformity coefficient is used to describe the tendency of the bulk of the particle size distribution curve, denoted by the symbol U, which is the ratio between the size represented by 40% of the sample and the effective size of 90% of the sample. The high coefficient of Uniformity indicates a lack of Uniformity of granular gradient. While the lower coefficient of Uniformity indicates a more uniform gradient.
When the regularity factor U is less than 3, the size of screen slots can be considered equal to the size of the sieve openings, which is equal to the size of the granules representing 40% of the sample. In the case of the Uniformity factor U between 3 and 6, the size of the screen slots is equal to the size of the granules representing 30% of the sample.
The size of the granular packs that are to be used around the screens is 5-8 times the size of the sample granules (aquifer sediment) in the same weight distribution.
If a prepackage is required around the screen, the size of the screen slots shall be equal to the size of the granules representing 90% of the volume of material used as gravel pack.
Sincerely
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