Experimental Comparison on Different Pile Load Testing Methods-Paper

Paper

Pdf Summary

The study compares two Osterberg cell load tests (OLTs) with three conventional top-down load tests (COLTs) on instrumented continuous flight auger piles in similar ground conditions near Naples. The site comprised made ground, pyroclastic sandy soils, and a volcanic tuff layer; vibrating-wire gauges measured axial loads along the piles, enabling comparison of overall response and local shaft load transfer.<br /><br />Overall, OLTs produced substantially stiffer pile–soil responses than COLTs, particularly at low loads. The difference diminished as load increased, and some test curves converged when shaft friction was fully mobilized. OLTs also permitted investigation of pile-base resistance over much larger displacements than the conventional tests. In the tuff socket, limiting shaft friction reached approximately 0.4–0.45 MPa; mobilized friction was lower in the surrounding sandy layers.<br /><br />Local comparisons showed that differences were concentrated near the pile head and base, while behavior in the middle portion was broadly similar. COLTs indicated greater stiffness in the upper layer, whereas OLTs showed greater stiffness in the bottom layer; results in the intermediate layer were variable. The authors suggest kentledge used in COLTs may increase confinement around the piles and influence measured shaft resistance.<br /><br />Because equivalent top-down curves derived from OLTs rely on assumptions about pile rigidity and the independence of shaft and base behavior, results from different testing procedures are not directly interchangeable. This matters especially for settlement predictions of pile groups, which may depend on a single pile’s initial stiffness. The study therefore recommends caution when using test data obtained by different methods.

Keywords

Osterberg cell load test

conventional top-down load test

continuous flight auger piles

pile-soil response

shaft friction

pile-base resistance

instrumented piles

vibrating-wire gauges

Naples ground conditions

settlement prediction