Chicago can be called the birthplace of the Skyscraper, and also tlle Drilled Shaft Foundation, both of which came into being late in the 19th century. The story of the Chicago Caisson begins with the presence of a thick deposit of soft clay beneath the City, and continues with the succession of building booms that have characterized the growth of the City over the last 140 years, beginning just after the Great Fire of 187 1. During that first boom, new tall structures were built so rapidly, and amid such profound geotechnical uncertainty, that the process of designing a successful foundation became one of trial and error, with very little time between projects to observe behavior and make corrections. Eventually attempts to float tall buildings on shallow foundations above the soft clay were abandoned in favor oftl,e first deep foundations, which bypassed the problem layer and found solid support on hardpan till or rock below. This paper will briefly describe the origin of the modem Drilled Shaft Foundation, which has its evolutionary roots in the Chicago Hand-Dug Caisson. It will then trace the development of the Chicago Caisson into a mechanized process, with each advance assisted again by observed behavior, emerging load test methods, and constant improvement and innovation in equipment and methods to meet the needs of the next generation of taller buildings
