A case study of bearing capacity of piles partially embedded in rock

Abstract

In the design of piles partially embedded in rock, the main factors that influence the strength and deformability of the rock and the transmission of loads from pile to rock are of utmost relevance to pile behavior. Most empirical methods were developed based on data from specific regions. Differences in geological conditions, drilling methods and other features are not considered in most procedures. The article deals with a case of piles partially embedded in rock located in the town of São Lourenço da Mata, Pernambuco, Brazil. The rock mass consists of ancient deposits, formed mainly by granites of different compositions, gneiss and schists. The deposits have been deformed by several tectonic processes. Results from 99 dynamic loading tests enabled comparison between the mobilized lateral and pile toe resistance, with the estimated capacity obtained from the design methods known in the literature. In the prediction, the lateral shear resistance due to pile penetration in residual soil was also considered. Because failure was not reached in the dynamic tests, the estimated capacity was higher than the mobilized resistance. The resistances mobilized by the pile shaft friction in soil, by the pile shaft friction in rock and by the mobilized toe resistance in rock in the dynamic loading tests are compared to design methods known in the literature. Five static loading tests indicated failure loads greater than the mobilized resistance in the dynamic methods. The comparisons allow recommendations of the most consistent design methods to use in similar cases in practice.