In artificial gravel pack design for irrigation tubewells, the Pack-to-Aquifer ratio ($P-A$ ratio) is defined as the ratio of the $50\%$ size ($D_{50}$) of the gravel pack to the $50\%$ size ($D_{50}$) of the aquifer formation. For stable sand control, the recommended $P-A$ ratio typically ranges between:
Options:
(A) $4 \text{ to } 6$
(B) $20 \text{ to } 30$
(C) $0.1 \text{ to } 0.5$
(D) $80 \text{ to } 100$
Answer Key:
A
Step-by-Step Solution & Explanation
A Pack-Aquifer ($P-A$) ratio between $4 \text{ to } 6$ (or $4 \text{ to } 9$ for uniform sands) provides the optimum balance: pores of the gravel pack are small enough to bridge and retain the aquifer sand particles, while remaining large enough to maximize permeability and prevent clogging. Option A is correct.