Performance Evaluation of CFA Vs. Bentonite Slurry Drilled Shafts Utilizing Drop Weight Testing

The performance of drilled shafts is known to be controlled by the type and quality of the construction methods. A comparison between different methods or different contractors is typically not available under the prevailing bidding and testing procedures. Six drilled shafts 0.70 m in diameter and 25.0 m long were installed and tested to structural failure at a site in Haifa, Israel. Three of the shafts were constructed using the Continuous Flight Auger (CFA) construction method and three of the drilled shafts were constructed using bentonite slurry. Site and shafts details are provided. The drop weight testing system is reviewed. Test results comparing the load carrying capacity of the shafts, load distribution and structural outlines are presented and discussed. While the bentonite slurry construction resulted in a more uniform constructed foundation capable of carrying higher load, the explanation to the variation at the given site conditions may be a result of the contractor's quality rather than advantages of one technology over another.