I will soon be involved with the foundation design of a 5 story concrete parking structure within 200' of a hospital building complex. The ground conditions, which have not been explored yet, are expected to consist of alluvial clays over weathered sedimentary rock lying at depths of 15' to 35' below the ground surface. The structural engineer and I are leaning towards supporting the structure on end-bearing augercast piles bearing on the rock. Two foundation contractors have told us they can install high capacity end-bearing augercast piles.
We are concerned about getting a clean surface for the end-bearing piles to rest on. I have seen some augercast piles installed in Oregon and all of the auger bits were deep "V" shaped with the concrete discharge point at least 1' above the bit tip (with these piles end-bearing was not important). These holes couldn't have been very clean.
Are there other auger bits being used in the industry that are very good for obtaining a clean hole and reliable? Are there bits being used which allow concrete to be discharged at the very bottom of the hole?
I would appreciate it if someone would share their personal thoughts and experiences with this or point me to some publications that deal with this subject. Thanks.
Your comment is justified, as I have had plenty of experience in what is called grout injected piles. The only way to be sure that a full bearing is achieved at the toe of grout,or concrete injected piles, is to, Inject a small quantity of grout or concrete,as the auger starts to lift. I have used one linial meter as a guide. Then stop injecting, and redrill into the injected material, insuring that the auger reached the original depth. The start injecting again, and complete the pour. This method insures that any loose material that is left as the auger is lifted first time, is mixed into the grout or concrete. We have extracted test piles, to inspect the shape at the toe, and the piles where redrilling was performed, had full flat bottoms. The piles that were poured in one lift, all were miss shapen, in some way, for the most part, they had only about half of the disturbed area concrete filled. Regards, Bill McGarry