Laboratory compaction of soils using a small mold procedure. (Division S-1--Soil Physics)

The compactability of a soil can be determined from parameters derived from laboratory compaction curves generated using the Proctor test. However, this is a destructive, time-consuming, and labor-expensive procedure. Our objective was to evaluate a new more rapid test to determine the maximum dry bulk density ([[rho].sup.Max.sub.b]) and soil water content at ([[rho].sup.Max.sub.b]) (SW[C.sub.Max]) from laboratory compaction curves using a mold with smaller dimensions than established for the standard procedure. Laboratory compaction curves were developed for nine soils with clay contents ranging from 232 to 385 g [kg.sup.-1] using the standard Proctor test procedure and the proposed procedure, which uses a 54-mm diam. mold and a 24.4 N rammer dropped from a height of 305 mm to produce a compactive effort (CE) of 109 kJ [m.sup.-3] [drop.sup.-1]. At a CE of 545 kJ [m.sup.-3], which is similar to the 540 kJ [m.sup.-3] produced by the standard test, the ([[rho].sup.Max.sub.b]) and SW[C.sub.Max] parameters derived from the proposed procedure were positively and significantly correlated with those derived from the standard Proctor test. With both procedures, ([[rho].sup.Max.sub.b]) decreased and SW[C.sub.Max], increased as the soil clay content increased. The small mold method did not affect the linear relationship between soil clay content and ([[rho].sup.Max.sub.b]). However, different relationships between SW[C.sub.Max] and clay content were observed, depending on the compaction procedure. Use of the small mold procedure requires less dry sieved soil, saves time, and labor in evaluating soil compactability. Based only on the reduction in rammer drops, use of the small mold procedure involves 15 times less labor requirements than the standard Proctor test.