1　概述1.1　钻孔扩底灌注桩发展史20世纪50年代后期在美国德克萨斯州首先成功地应用小直径钻扩桩[1]。此后,印度、前苏联、英国等也将小直径钻扩桩成功地用于工程实践中。我国于1966年在“三线”某冶金建设工程中推广应用近600根小直径钻扩桩。80年代初,北京市桩基研究小组在6 1 OVERVIEW 1.1 History of Bored Piles with Bored Piles The first successful application of small diameter drilled and expanded piles in the late 1950s in Texas, USA [1]. Since then, India, the former Soviet Union, Britain and others have also successfully used small-diameter drill-piles in engineering practice. In 1966, China popularized and applied nearly 600 small-diameter drill-expanded piles in a metallurgical construction project of “the third line”. In the early 1980s, Beijing pile foundation research group in 6