Abstract：In order to put forward a theoretical formula to calculate the spacing of the sand-stone compaction piles on sandy ground，some previous engineering practices and field tests on the composite foundation with sand-stone compaction piles are studied. As the reinforcement effects of soil at the pile tip and around the pile shaft are noticed. A new concept，reinforcement depth at the pile tip，is put forward. Based on the constant volume of soil grain before and after the foundation reinforcement，a new method is theoretically investigated to estimate the piles spacing taking both the lateral and vertical compaction and vibration effects at the pile tip into account. The method correlated the calculation of pile spacing with standard penetration test(SPT) blow counts as well as the fine-grained content to facilitate its use in engineering practice and design. By comparing the results of a case gained by previous and present methods respectively，the reasonability of the method is testified.
