Laboratory investigation of efficiency of conical-based pounders for dynamic compaction

The pounder for dynamic compaction is conventionally built to have a flat bottom. An innovative idea of using a conical-based pounder to improve the efficiency of dynamic compaction has been investigated, and the results are presented in this paper. Both a conical-based pounder and a flat-based pounder were used in an extensive programme of laboratory dynamic compaction tests. An air pluviation technique was used to prepare dry sand specimens, 60 cm in diameter and 50 cm high, to have initial relative densities of 30% and 40%. Wet sand specimens with an initial relative density of 60% were prepared from the dry sand specimens. A total of 14 dynamic compaction tests were performed. The results of each test include dimensions of the crater, heave around the crater, and cone penetration resistance at 13 penetration locations. It is found from the test results that the efficiency of dynamic compaction with the conical-based pounder depends on both the grain size characteristics and the volume change behaviour of the sand. The conical-based pounder is more effective in the Mai-Liao fine sand with 8% fines than in the clean Ottawa medium sand.