Abstract：Dynamic compaction analysis is usually based on time-domain. The energy method is used to calculate and analyze the dynamic response of foundation under dynamic compaction within frequency-domain. Since the modes of foundation are dense，by taking the criterion of energy response as mode truncation index, the energy norm and criterion are established to calculate the mode truncated order of dynamic compaction response. According to energy equation，the response regulation of kinetic energy and strain energy during dynamic compaction is studied. The results show that most of the compaction energy is changed into wave energy. It is considered that the deep soil is mainly under the effect of wave energy tough the surface soil is under the compaction force directly.
