Shaft Friction between Marble and Concretein Rock-Socketted Large Diameter Bored Pile: A Review of State of Art

Abstract

In Hong Kong, although rock-socketted steel H-piles and large diameter bored piles have widelybeen employed as foundation, limited local experience and design parameters have been published for the piles installed in cavernous karst area. According to the Code of Practice for Foundations (2004) issued by the Buildings Department, the allowable bearing pressure for Grade III or better granitic or volcanic rock and the allowable shaft friction between the rock and concrete for pile in the socket are set out at 5MPa and 0.7MPa respectively. Theoretical studies and/or in-situ measurements overseas by Serrano and Olalla (2004, 2006), Neoh (1998) and Kutschke et al (2004) noted that the shaft friction varies, and in some cases, the allowable shaft friction can be lower than 0.5MPa. Studies have also been carried out in marble with and without infill content, and an allowable value between marble and concrete pile of 0.3-0.5MPa was suggested (Domanski et al 2002; Domanski and Au-yong 2004). This paper reviewed the state of art on these parameters, especially that on the allowable shaft friction between marble and concrete pile in the socket. In view of the limited publication on the local experience and design parameters of the widely used rock-socketted piles in cavernous karst area, a value of 0.3MPa may be adopted as the allowable shaft friction between marble and concrete pile at the socket section; but this value is a rather conservative one and hence instrumentation to verify the value is being carried out in a project in the cavernous karst in Tin Shui Wai, Hong Kong.