Hello,

For a CFA pile designed as end-bearing on rock, is a full rebar cage necessary for the full length of the pile or is it okay to use the typical CFA reinforcement scheme of a full cage in the upper 1/3 of the pile and only extending a full-length center bar to the bottom of the pile?

Is there any concern for the center bar buckling due to fact that there is no lateral confinement reinforcement i.e. spirals or ties? I know the FHWA micropile manual recommends limiting the steel yield strength to 87 ksi due to the issue of strain compatibility between the grout and the rebar. I believe this is to prevent the grout from cracking due to excessive compressive strain but I don't know if this necessarily addresses the issue of rebar buckling. The scenario I'm envisioning in my head is that the grout will not provide sufficient confinement to the center bar, and the grout will crack and the center bar will buckle, i.e. local buckling of the rebar as opposed to global buckling of the pile. Is there any legitimacy to this concern or is it safe to assume that as long as the soils above rock have sufficient strength to prevent global buckling of the pile then there is no need to worry about local buckling of the rebar?

Are there any other concerns with only using a single center bar for an end-bearing drilled pile?

Thanks!