SEISMIC RESPONSE CHARACTERISTICS OF FOUNDATION COMPOSED OF MICROPILES AND SOILBAGS AND ITS SUPERIORITY TO PILE FOUNDATION

Abstract

 The authors have proposed foundation composed of micropiles and soilbags as a new foundation type. The foundation is characterized by laying soilbags on the pile head and constructing structures on the soilbags. The expected effects are omission of junction structures of piles and footing, reduction of diameter of piles, and reduction of response acceleration of structures. In this study, seismic response evaluation method for the proposed structure of actual size was constructed, and the seismic responses of the proposed foundation and pile foundation were compared on the different conditions of input acceleration and height of pier. From analytical results, except for the case where the pier height is low, it was found that the prolonged period due to the lifting of the footing resulted in the effect of peaking the response acceleration of a pier and the effect of suppressing the flexural moment at the base of the pier compared to the pile foundation. It was also found that the response displacement of the proposed structure was almost the same as that of the pile foundation, and that the residual displacement of the proposed structure was smaller than that of the pile foundation. Moreover, it was clarified that the effect of suppression of flexural moment of piles was expected by laying soilbags.