Study on the Bearing Capacity of Bored Piles with Improvement Techniques-Paper

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The study evaluates bored piles improved with rings along the shaft and consolidation of the pile toe, a technique developed for local soil conditions in Maceió, Brazil. Toe consolidation mixes added concrete with loose soil at the bottom of the borehole, aiming to improve base resistance.<br /><br />The authors analyzed load-test data from 16 piles using two load–settlement curve extrapolation methods (Van der Veen and Décourt) and two semi-empirical methods (Aoki–Velloso and Décourt–Quaresma). The semi-empirical methods were run with different assumed capacity increases to represent the combined improvements. Some piles were excluded from particular comparisons because their results were anomalous or the toe resistance was not mobilized during testing.<br /><br />The Décourt stiffness method generally produced less conservative ultimate-capacity estimates than Van der Veen, but its separation of shaft and toe resistance did not show a consistent pattern. Overall, the improved piles appeared to mobilize shaft and base resistance at broadly similar load levels.<br /><br />Compared with Van der Veen estimates, the Décourt–Quaresma method using a 60% capacity increase gave the most representative results: 92% of the evaluated piles fell within the study’s accepted range. The authors therefore conclude that this method is the best of those tested for estimating capacity of piles with both shaft rings and toe consolidation. The 60% increase exceeds the 30–40% commonly used by local designers and was considered consistent with structural safety when the resulting capacity is divided by a factor of safety of 2.<br /><br />The authors recommend further research with more piles, instrumented load tests, investigation of soil–concrete interaction, and tests of toe consolidation without shaft rings.

Keywords

bored piles

shaft rings

toe consolidation

load-test data

ultimate capacity

Van der Veen

Décourt method

Aoki–Velloso

Décourt–Quaresma

Maceió Brazil