Abstract: A soil compactor for laboratory use to systematically and controllably coct specimens of soil and earth-rock mixture materials. The raising of a drop hammer after each strike to a pre-selected height is accomplished automatically by the use of a pneumatic cylinder in conjunction with sensing valves. A counter and deactivation valve are also provided so that the system will automatically shut off after the hammer drops a pre-determined number of times. Uniform compaction of each specimen is ensured by automatically rotating the specimen a pre-selected number of degrees after each strike by the hammer. The compactor is also vertically and horizontally adjustable so that specimens of various heights and widths can be accommodated.