Response of tapered piles subjected to lateral loading

Abstract

Eighteen lateral loading tests were conducted on large-scale steel piles to establish the lateral behaviour of tapered piles in cohesionless soil. Three piles 1.52 m in length with different taper angles but the same average embedded diameter of 168 mm were installed in sand enclosed in a steel chamber 1.5 m in diameter and 1.445 m in depth. The soil chamber was lined with an air bladder so that sand inside the chamber could be pressurized to vary the confining pressure. The piles were instrumented with electrical resistance strain gauges and the horizontal pile movements at grade and the loading point were measured with displacement transducers. The bending-moment functions along the pile were calculated from the strain measurements by curve fitting the measured strain data. The soil resistance (p) and pile displacement (y) relationships were developed in the form of p-y curves by differentiating and integrating these bending-moment functions. It was found that tapered piles carried up to 77% more lateral loads than straight-sided-wall piles with the same average diameter. The maximum bending moment occurred in all piles at almost the same depth of one third of the embedded length of the pile. Hence, the cross section of tapered piles at the location of maximum bending moment was larger than that of straight-sided-wall piles, resulting in lower stresses in the pile. It was concluded that the tapered piles represent a more efficient distribution of the pile material and display better performance under lateral loading conditions.Key words: tapered piles, lateral response, p-y curves, modulus of subgrade reaction.