Relative Compaction from Field Density and Proctor Maximum

The pass/fail an earthwork inspector reads at every test point: RC = (field dry density / Proctor max) x 100, with the field dry density backed out of the nuclear-gauge wet density and moisture, gamma_d = gamma_wet/(1 + w). 128 pcf wet at 12% against a 120 pcf Proctor gives 114.3 pcf dry -> 95.2%, passing a 95% structural-fill spec; the same wet density at 16% moisture fails at 91.9% - the moisture reading is as important as the density, why over-wet fill is rejected. Enter the Proctor maximum (D698 / D1557). A QC aid; the geotechnical spec governs.

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Formula and source

gd_field = wet / (1 + w/100); RC = gd_field / max x 100; pass when RC >= spec.

The relative-compaction relation RC = (gamma_d,field / gamma_d,max) x 100 with the moisture-back-out of field dry density and the ASTM D698/D1557 Proctor basis, a standard earthwork-QC result, by name.

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