A design method for drilled piers in soft rock

Abstract

A new procedure for the design of drilled piers socketed into soft rock is presented and the selection of design parameters discussed. The design method is based on (1) satisfying a specified design settlement criterion and (2) checking to ensure that there is an adequate factor of safety against collapse. The design allows consideration of the possibility of some slip occurring at the pier–rock interface under working load conditions.The design procedure is illustrated by a series of detailed calculations relating to two piers in Queenston shale and the observed behaviour of these piers is compared with design expectations. It is shown that these piers satisfied the design settlement criterion while having a significant proven factor of safety against collapse. Key words: rock, piers, piles, settlement, bearing capacity, design.