The Continuous Helical Displacement (CHD) pile is an auger displacement pile developed by Roger Bullivant Ltd in the UK. The CHD pile is installed in-situ through the use of a drilling auger, in a similar fashion to European screw piles and as such, it has performance characteristics of both displacement and non-displacement piles Based on field experience, it is known that the load capacity performance of the CHD pile significantly exceeds the current design predictions, particularly when installed in sand. Model CHD piles were created in pluviated test beds at a range of different densities and compared to model displacement and non-displacement piles. The load tests show that the CHD piles have a similar ultimate capacity to displacement piles. Instrumentation of the model piles allowed load distribution throughout the pile length to be determined. The tests allowed design parameters to be established, with it being shown that the CHD has lower bearing capacity factors and higher earth pressure coefficients than current suggestions .The disturbance to the in-situ soil conditions caused by the installation of the CHD piles was measured using a model CPT probe. The CHD pile was found to cause significant changes in soil relative density laterally around the pile shaft while displacement piles show changes predominantly below the pile base. The CHD pile is found to cause a densification of the in situ soil for all relative densities with the greatest increase occurring in loose sand. The ultimate capacity of the CHD pile is determined from load tests carried out on field CHD piles with the aid of capacity prediction methods for piles which have not been loaded to their ultimate capacity. The results from model testing have been applied to field pile tests to allow the development of design parameters including appropriate pile diameter, bearing capacity factor Nq and the earth pressure coefficient k which are suitable for CHD piles.
|Date of Award||2012|
|Supervisor||Michael Brown (Supervisor)|
- Auger displacement
- Model testing
- Field data