feet of soil, and calls for compaction of three separate lifts of soil using 25 blows by a 5.5 lb hammer falling 12 inches, for a compactive effort of 12,375 ft-lbf/ft3. The "Modified Proctor" test, ASTM D1557 / AASHTO T180, uses same mould, but uses a 10 lb. hammer falling through 18 inches, with 25 blows on each of five lifts, for a compactive effort of about 56,250 ft-lbf/ft3. Both tests allow the use of a larger mould, 6 inches in diameter and holding 1/13.333 ft3, if the soil or aggregate contains too large a proportion of gravel-sized particles to allow repeatability with the 4-inch mould. To provide about the same theoretical compactive effort (12,320 ft-lbf/ft3 for standard Proctor and 56,000 ft-lbf/ft3 for modified Proctor), the number of blows per lift is increased to 56. Alternative compaction testing The California Department of Transportation has developed a similar test, California Test 216, which measures the maximum wet density, and controls the compactive effort based on the length (in fact the height) of the test sample and not on its volume. The primary advantage of this test is that maximum density test results are available sooner, as evaporation of the compacted sample is not necessary. References See also Civil engineering Earthworks (engineering) Geotechnical engineering Granular material Publications in geotechnical engineering Soil compaction Soil mechanics Tests in geotechnical laboratories