Skin Friction and End Bearing Parameters of Cast-in-Place Concrete Piles Socketed into Calgary Bedrock

ABSTRACT: The bedrock in the Calgary area belongs to the Paskapoo or Porcupine Hills Formations. Both formations are similar in depositional environment and geotechnical properties and consist of sandstone (SS), siltstone (SI), and claystone (CS). Due to the shallow depth of bedrock at several locations throughout the Calgary area, rock socket Cast-In-Place (CIP) concrete piles provide a preferred foundation option for major infrastructure projects in Calgary. This paper presents a comparison between the design parameters for rock socket CIP concrete piles calculated from the Unconfined Compression Strength (qu) of the bedrock and the back calculated parameters from full scale instrumented pile load tests. The qu of the bedrock employed in the comparison was obtained from laboratory tests on good quality bedrock core samples extracted from different areas in Calgary. The back calculated design parameters were obtained from two full scale load tests carried out on pre-production rock socket CIP concrete piles at the Stoney Transit Facility (STF) project in Calgary. The comparison showed that the skin friction and end bearing parameters of rock socket CIP concrete piles are underestimated when calculated from the laboratory qu results of the bedrock core. The results suggest that the in-situ shear strength of Calgary bedrock is higher than the shear strength of the bedrock obtained from the laboratory tests by two to three times. This may be attributed to the potential disintegration and swelling of the bedrock taking place during coring, sampling, and transportation of the samples to the laboratory for testing.