Abstract: The plastic analysis of compacted pile under hole-blasting and tamping processes based on the unified strength theory is investigated.The effects of strength difference in tension and compression and the effects of intermediate principal stress are both considered.The formulae thus obtained are suitable for materials with different tension & compression strengths as well as those with equal tension-compression strengths.The formulae can be used to predict soil plastic zone during hole-blasting and tamping processes.The deformation characteristics of nearby piles in hole-blasting process of one pile can be estimated based on the solution.Thus the weight of column hammer and tamping numbers can be decided.