CFA and reinforcement

[steveyeung]

I am working on a bridge project and the foundation is that: bored piles of 600mm diameter will rest on clalk which is covered a 12m thick soft made ground. A geotechnical engineer said "it would be difficult to lower (the bottom of) a reinforcement cage deep down to the pile base if the pile is socketed into the chalk by 3m and the hole is bored by a CFA."

Could geot guy tell me why???

 

[civilperson]

A continuous flight auger must be removed from the excavation before placing the reinforcement. The hole will collapse or slough in causing the cage to set on spilled soil. A casing left in plce will prevent the problems associated with soft soils and sloughing. Some proceedures remove the casing as the the concrete is filling the pile volume, but I recommend that it stay in place.