RESEARCH ON UNDER-REAMED EQUIPMENT-DEVELOPMENT HISTORY AND PRESENT SITUATION

Abstract

Cast-in-place concrete piles with bell bottoms have been developed in the United States and Europe since the 1890s to reduce the pressure on a bearing stratum to allowable limits. At the beginning, bell bottoms were excavated by hand, but belling tools or underreamers were also used. In Europe, machines to enlarge pile bases were introduced at a symposium on cast-in-place piles held in London 1966. In Japan, methods and equipment to build very long cast-in-place concrete piles with enlarged bases have been developed and become popular since 1971. After revewing the methods and equipment to build piles with enlarged bases developed in the world, the author introduces the recent trench.