Analysis on bearing performance of Y-shaped piles under compressive and tensile loading

Y-shaped piles, characterised by three concave arches, are adopted in practice as they exhibit advantages over conventional circular piles. To facilitate their practical design, eight model tests were conducted in dry sand on Y-shaped piles (Y₁ and Y₂) and circular cross-sectional piles (C₁ with the same section area A_p as pile Y₂ and C₂ with larger A_p but the same perimeter as Y₂). Under compressive or tensile load, the tests provided load–settlement (displacement) data and the distributions of resistance along the pile shaft and at the pile base. The tests revealed the expansion (compressive loading) and contraction (tensile loading) effects on the pile capacity for the Y-shaped sections. Pile Y₂ had a 70% larger ultimate capacity than pile C₁. It induced a shaft resistance over 100% larger than that of C₁ and 15% larger than that of C₂. The ratio of ultimate tensile capacity to ultimate capacity (about 0·15) of the short Y-shaped piles was much lower than that of in situ piles. A simple expression considering shape effects was established to estimate the ultimate capacity of a pile under compressive loading and the results compared well with the model tests. Compared with the circular piles, the Y-shaped piles showed increases of 15% and 30% in shaft and base resistance, respectively, for compressive loading.