In construction of gravel packed wells, the pack-aquifer ratio is generally defined as ______.
GATE AG - 2022,
Answer: A
The pack-aquifer ratio is the 50% size of the gravel pack divided by the 50% size of the aquifer material.
In gravel-packed well design the pack is graded against the aquifer by comparing their median (\(D_{50}\)) grain sizes, the size at which 50% of the material is finer. The ratio of the pack’s median size to the aquifer’s median size is the pack-aquifer ratio, and design criteria keep it within a recommended range so that the pack holds back the aquifer sand while staying permeable.
The inverted ratios, aquifer over pack, would be less than 1 for any working pack. The 60% and 10% sizes are used for a different measure, the uniformity coefficient \(D_{60}/D_{10}\) of a single material, not for comparing pack with aquifer.
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