A Study on the Deformation Characteristics of Foundation Ground reinforced with Micropiles.

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The aim of this study is to clarify the mechanism of bearing capacity of Micropile Foundation on sand ground. A series of model loading tests were conducted, where the footing reinforced with a group of micropiles were subjected to vertical and inclined loads. The behavior of the Micropile Foundation was observed and comparatively examined. The effects of the relative density of sand ground, the length and stiffness of micropile, the number and inclination of micropiles on the bearing capacity were focused. The conclusion concerned with the interaction between footing and a group micropiles derived from the test results is summarized as follows ;- The significant effect of group micropile was recognized on the improvement of bearing capacity by the reinforcement of foundation ground with micropiles. The effect was emphasized in dense, dilatant ground.- Due to the interaction between footing and group micropiles, the ground material beneath the footing is confined, and the confining pressure and shear strength raised.- To mobilize the confining effect of the interaction, dilatancy of ground material, sufficient number of micropiles and bending stiffness of micropiles are dispensable.- In the case of vertical load, the improvement of bearing capacity by group micropiles appeared under the certain amount settlement of footing. In the case of inclined load, the improvement of bearing capacity was not recognized under the ordinary condition due to the lack of base pressure of footing.- It was found that initial base pressure is indispensable for the stable improvement of bearing capacity. Then the application of pre-tension on the micropiles and a complimentary rise in base pressure is effective measure for the construction of earthquake resistant micropile foundation.