Developing an Efficiency Equation for Tapered Pile Groups in Sand Using Mathematical and Numerical Analyses

Abstract

AbstractThis study presents a new simple equation for prediction of pile group efficiency considering the effect of tapering angle in cohesionless soil under vertical loading. Firstly, a simple analytical relationship based on the mathematical definition of the pile group efficiency is developed. However, the effect of tapering angle is captured by defining a new geometry efficiency coefficient associated with the shaft vertical bearing component of tapered piles. Thereafter, a mathematical equation is developed by taking into account the shaft vertical bearing ratio and the new geometry efficiency coefficient. On the other hand, a numerical analysis is performed for modelling a single bored cylindrical pile and a tapered pile with the same volume as well as bored tapered pile groups to validate the proposed mathematical equation. The UBC sand constitutive model is adopted for the modelling of piles in loose Cambria sand. Subsequently, the load-displacement diagrams of single and group of piles are obtained. Then, the bearing capacities of cylindrical and tapered bored piles both as single and group are computed and compared, using a specific settlement criterion. Besides, the friction resistance ratio and the shaft vertical bearing ratio are separated, applying numerical methods. Having calculated the ratios of various components of bearing capacity, pile group efficiencies can be obtained from both numerical and mathematical models. The results show that the proposed equation can predict the pile group efficiency incorporating the tapering angle as well as other influencing parameters as a simple and novel relationship.KeywordsPile groupEfficiency coefficientLoad capacitySettlementFinite element modelAxial loading