High-capacity ribbed pile foundations

Abstract

This is the published version of the paper.This version of the publication may differ from the final published version. This research concerns the influence of ribs on the ultimate capacity of a bored pile in overconsolidated clay. Ribbed bored piles are known to give increased shaft capacity in comparison to conventional straight-shafted bored piles. The investigation seeks to explore the effectiveness of ribs at increasing the ultimate capacity of a pile, and furthermore to understand how this enhanced capacity is derived. The scale pile test results are analysed using several industry standard methods. A plastic failure envelope for the base of the pile rib is identified. This plastic failure envelope is used to provide a detailed design solution for the ultimate capacity of a ribbed pile. The design solution is simple and requires a summation of the constitutive contributions from each rib and from the base and shaft of the pile. This method has been used successfully to predict the ultimate capacity of any pile tested to within ±8%. Permanent repository link

An experimental study into the ultimate capacity of an ‘impression’ pile in clay

“…Once the impressions were completed, the piles were cast using a polyurethane fast cast resin, Sika Biresin G27 (McNamara, 2001;McNamara and Taylor, 2002;Gorasia and McNamara, 2016). Aluminium powder was used as filler to increase the weight of the pile.…”

“…The slight increase in critical spacing is probably due to the different failure mechanism for these anchor plates. Both Gorasia and McNamara (2016) and Qian et al (2016) found that ribbed piles have a higher capacity than straight piles with a diameter equal to the outer diameter of the ribbed pile.…”

“…The ribs were found to enhance the ultimate capacity of 750mm diameter piles, constructed in glacial clay, by as much as 30%. Gorasia and McNamara (2016) presented the results of a series of centrifuge tests on ribbed piles demonstrating that the capacity increase could reach 40% for a pile 800mm in diameter with ribs protruding by 75mm (at prototype scale). Small scale tests by Qian et al (2016) demonstrated that the pull-out capacity of a ribbed helical pile in sand, 50mm in diameter and with rib length of 8 mm, may be up to 5 times higher than that of a straight plain pile.…”

Editorial

“…The next paper by Qian et al (2017) describes the results of laboratory tests on model helical ribbed piles (Figure 1) and finite-element analyses to investigate the soil-pile interaction mechanism and how the pull-out resistance of piles is increased by the ribs and varies with rib spacing. Gorasia and McNamara (2016) have also published a paper in this journal on ribbed piles, but investigated their bearing capacity rather than tensile resistance.…”

Editorial

“…The last paper to be concerned with piled foundations in this issue is the fourth one, by Gorasia and McNamara (2016). Piles with enhanced shaft capacity obtained by adding outward protruding ribs, so-called ribbed piles, are considered.…”