Many old foundations, which required to be retrofitted because of poor in seismic performance, are still in service. Seismic performance of exist foundation can be improved by installing sheet-piles around footing and connecting together. Basing on this idea, authors proposed new seismic retrofitting method. This paper describes about seismic proving tests, both lateral loading tests and shaking table tests, to clarify the improvement effects on the seismic performance of the pile foundation utilizing the proposed method. Basing on the test results, in addition, the mechanism for improvement is discussed. Following outcomes were found. (1) Reduction in section force of exist pile is confirmed by the proposed method. This improvement is seen not only pile cap, but also the section deeper than sheet-pile depth. (2) Sub grade reaction of exist piles may be reduced because lateral resistance of the foundation mainly shared by additional sheet-piles instead of piles.
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