Load Transfer in an End-Bearing Auger-Cast Pile: Laboratory-Scale Single-Pile Tests and Numerical Simulation

This study examines the load transfer behavior of Single Auger Cast Piles (ACPs) through a combination of physical model testing and numerical modeling, replicating laboratory-controlled conditions. The research aims to enhance the understanding of axial load distribution in ACPs installed in layered soil profiles, particularly where a weak overburden is underlain by a stiffer geomaterial. The physical modeling involved testing single ACPs embedded in a synthetic limestone layer designed to simulate weathered Florida limestone. The ACPs were installed using a motor connected to a hollow stem auger with a hose inside, with grout pumped during auger extraction to replicate field installation procedures and ensure consistent soil-pile interface conditions. Instrumentation, including a pressure cell, Linear Variable Differential Transformers (LVDTs), and strain gages, was deployed to monitor stress distribution, pile displacement, and axial load transfer along the embedded length. In addition to reporting global load–displacement behavior, we compute unit shaft resistance directly from embedded strain gages by converting measured strain to axial-load profiles and differencing adjacent gages with depth. This axial-load-profile method quantifies the limited shaft contribution in the overlying loose sand and the dominant end-bearing in the synthetic limestone socket. Load testing followed a displacement-controlled procedure conforming to ASTM D1143. The experimental results indicated that load transfer was predominantly governed by end-bearing resistance, with minimal shaft friction contribution in the overlying sand layer. This behavior is attributed to the limited interface shear resistance between the grout shaft and the relatively loose granular medium. Numerical modeling of a single ACP was conducted using PLAXIS 3D, replicating the physical test conditions to evaluate stress distribution, axial load transfer, and soil-pile interaction. The numerical model was subjected to incremental displacement-controlled loading, consistent with laboratory conditions, and the simulated load-settlement response was compared with experimental measurements.