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 for cast-in-situ bored piles constructed with temporary casing, permanent casing, with bentonite support or with no support. Pile shaft capacity predictions were based on parameters derived from borehole information, insitu and laboratory test results. Ground conditions comprised alluvium and residual soils overlying argillite bedrock. The piles were designed to be self supporting open bored piles with temporary casing, as necessary. However to overcome problems with side wall collapse during construction, bentonite support or permanent casing was proposed. This lead to concerns regarding the appropriateness of the design parameters from bentonite cake on pile sidewalls. Pile load testing was carried out using high strain dynamic test methods on piles constructed using casing and bentonite. The results of the tests for the various support conditions and construction methodology are discussed with reference to the adopted design values. The case study illustrates that where constructed with appropriate controls, bentonite support does not reduce the mobilised skin friction when compared to other methods of construction. Where poor construction techniques were employed and where construction time was excessive, poorer than expected performance may result.