Due to limitations of equipment size, compaction characteristics of earth-rock materials are usually determined by laboratory tests of samples contained in small molds and having maximum particle diameters less than those of the in situ soil. Corps of Engineers' laboratories perform such tests on samples from which oversized particles have been scalped and replaced, assuming that test results are comparable to those that would have been obtained on full-scale samples. The purpose of this investigation was to determine effects on compaction characteristics of earth-rock mixtures due to the size of compaction equipment used and the altered gradation resulting from the scalping and replacement procedure. A mechanical compactor equipped with 18-, 12-, and 6-in.-diam molds and 5.5- and 24.7-lb rammers having diameters of 2.0 and 6.0 in., respectively, was utilized for the testing. Comparative tests were performed with a hand-held hammer utilizing standard procedures. Materials tested were Vicksburg silty clay (CL) having LL = 43 and PL = 22 and a clayey sandy gravel (GC) (LL = 37 and PL = 14) with maximum particle size of approximately 3 in. from DeGray Dam in Arkansas. Samples of the CL material were batched using either a commercial kitchen mixer or a pugmill. All of the CL specimens were compacted in three layers using compactive efforts approximately equal to the standard effort (12,300 ft-lb/cubic feet) by adjusting the number of blows. A total of seven compaction curves were developed for the Vicksburg silty clay (CL) and six compaction curves were developed for the clayey sandy gravel.
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