Comparison of Pile Shaft Capacity Predictions vs Test Results for Different Construction Methods and Different Construction Time

摘要

This paper presents a comparison of pile shaft capacity predictions and dynamic load test results forrncast-in-situ bored piles constructed with temporary casing, permanent casing, with bentonite support orrnwith no support. Pile shaft capacity predictions were based on parameters derived from boreholerninformation, insitu and laboratory test results. Ground conditions comprised alluvium and residual soilsrnoverlying argillite bedrock. The piles were designed to be self supporting open bored piles withrntemporary casing, as necessary. However to overcome problems with side wall collapse duringrnconstruction, bentonite support or permanent casing was proposed. This lead to concerns regardingrnthe appropriateness of the design parameters from bentonite cake on pile sidewalls. Pile load testingrnwas carried out using high strain dynamic test methods on piles constructed using casing andrnbentonite. The results of the tests for the various support conditions and construction methodology arerndiscussed with reference to the adopted design values. The case study illustrates that wherernconstructed with appropriate controls, bentonite support does not reduce the mobilised skin frictionrnwhen compared to other methods of construction. Where poor construction techniques were employedrnand where construction time was excessive, poorer than expected performance may result.