Newcastle Chapter

Drilled Shaft Instrumentation for O-cell Tests

Fitri Johari

The O–Cell is a device for determining inplace drilled shaft skin friction and end bearing. It can be used in single or multi-layer stratigraphy and is generally more convenient than traditional load testing methods.

In this talk, the general requirements for O-cell instrumentation will be presented, including the differences in instrumentation required for O-cell bi-directional static load tests vs. conventional load tests, purpose and numbers of various embedded instruments, and instrumentation to obtain additional geotechnical parameters. The advantages and limitations of single/multi-level O-cell tests will also be presented.
The added value gained from including strain gauge and extensometer instrumentation for installations, particularly for locations with multi-layer stratigraphy, for assessment of load distribution along the shaft will also be discussed. Practical details on the locations and number of strain gauges and the use of retrievable gauges in Cross Hole Sonic Logging (CHSL) pipes will be presented.

Calculation procedures for determining skin friction and end bearing will also be discussed. This includes methods for the construction of the top-loaded load- displacement behaviour, such as using the computation methods of summing the measured behaviour or summing the modelled behaviour. The importance of actual pile section area, the use of tangent stiffness in the assessment of pile stiffness values and an introduction to the Sonicaliper® will also be presented.

Drilled Shaft integrity testing will also be discussed.

Speaker biography

Fitri graduated from the University of Wales with a 1st Class Honors Degree in
Civil Engineering in 1988. He has worked on piling projects in both engineering, quality control, and contracting in a variety of countries including the UK, Hong Kong, Malaysia, Singapore, Bahrain, and Qatar for various companies and types of piles. He has been involved with O-Cell testing since 2001.

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