Abstract: This paper presents a case history of a deep foundation installation in Yibin City of southern Sichuan Province. The bored pile installation techniques, such as, rotary drilling of the bored concrete pile under wet conditions, slurry method and long casing method for the maintenance of the borehole stability are introduced in the paper. Then the optimum mud-water ratio was selected, bentonite slurry borehole stability technology was utilized to minimize the probability of borehole caving. The use of long casing effectively resolved defects in the bored pile installations, such as, connecting of adjacent bored piles, difficulties of slurry circulation return, and dirty concrete at the pile head so that the strength of the concrete at pile head lower than the required. The paper also proposes some bored pile installation suggestions such as, pile head treatment, difficulties encountered in the long casing withdrew. The improved pile head treatment methods, such as, temporary cofferdam and/or splitable short casing at bored pile head are proposed for the low pile head issues and improved the bored pile head installation quality. 

Key words: Boring Methods, Long Casing, Borehole Protection with Slurries, Bored Pile Integrity Tests