Evaluation of Soil Mechanics Laboratory Equipment. Report 12. Modified Berkeley Pneumatic Tamper for Compacting Test Specimens of Cohesive Soils

Difficulties have been encountered in reproducing sufficiently similar dry unit weights (within plus or minus 0.3 pcf) in 1.4-in.-diam triaxial test specimens of cohesive soil compacted using the spring-loaded Harvard miniature compactor. In an effort to alleviate these difficulties, a tamper was made which maintained a constant force on the compacting foot by air pressure acting on a rolling diaphragm. It is designated as the 'modified Berkeley pneumatic tamper.' Calibration and operation showed the pneumatic tamper to be a significant improvement over the spring-loaded tamper. The tamper permits rapid and precise adjustment of the tamping force, with assurance that the tamping force actually applied to the soil is the same for each tamp even when used by different operators. It is believed that laboratories preparing test specimens of cohesive soils by kneading compaction can improve the quality and efficiency of this activity by using a pneumatic tamper.