Annular Grout Volume for Cased Bore / Pipe-in-Casing
The grout volume in the ring between a bored casing and the carrier pipe: annular area = pi/4 (bore^2 - carrier^2), volume = area x length grossed for waste. A 24 in bore around a 16 in carrier over 100 ft is a 6.46 cy ring (1,306 gal), ~6.79 cy ordered. The field always overruns the neat annulus.
Formula and source
annular_area_in2 = (pi/4) x (bore_dia_in^2 - carrier_od_in^2); neat_ft3 = annular_area_in2 / 144 x length_ft; grout_cy = neat_ft3 / 27 x (1 + waste_pct/100); grout_gal = neat_ft3 x 7.48052 x (1 + waste_pct/100).
Annular-area identity by name (ring between two concentric circles); first-principles volume arithmetic.
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