by Yue Choong Kog, construction manager, Suntec City Development, Singapore. This paper was first published in GE’s April 1990 edition.
Most piles that are embedded in a consolidating soil layer are required to transmit an imposed axial load from the pile top to the supporting media. A detailed investigation of a case study on downdrag and axial load on piles in layered soils is presented where failure of piles was reported due to the combined action of surcharge and axial load. The interaction of downdrag and axial load as well as the combined effect on the pile force distribution along the pile shaft is discussed. For economical design of piled foundations, not all piles need to be designed for negative skin friction even though large consolidation settlement is anticipated. Based on detailed investigation of the case study presented, the governing criterion where downdrag must be accounted for in the design of piled foundations is established.