Abstract:In order to analyze the influence of the situation that two rams impact one by one in a cycle on impact force for pile hammer, numerical analysis model for combination pile hammer which consists of upper ram and lower ram was presented. In the model, different variable lumped masses were used as upper ram, lower ram, anvil and pile cap, different variable springs and dashpots were used as the middle cushion and ram cushion, a spring was used as pile cushion and a dashpot was used as pile. Numerical solution for the impact force was analyzed by dimensional analysis, the separation of ram from the cushion and the separation of the pile from the pile cushion were considered, the influence of combination pile hammer parameters on impact force was analyzed, and the impact force generated by common pile hammer and combination pile hammer were compared. Results show that the combination hammer structure causes a lower crest and a longer effective impact time as it has more than one force wave.