Required rock socket embedment for Caissons (to develop fixity)?
Required rock socket embedment for Caissons (to develop fixity)?
(OP)
It seems like everyone uses 1 Diameter of embedment to achieve this (i.e. fixity of the caisson to the rock). But I could have sworn I read (somewhere) that research has indicated that anywhere from 1 to 3 diameters may be required. Can anyone recommend a (reliable) reference? Thanks in advance!






RE: Required rock socket embedment for Caissons (to develop fixity)?
I would suggest posting this on the Foundation engineering Forum to get some advice from the geotechs.
RE: Required rock socket embedment for Caissons (to develop fixity)?
The soil/rock lateral stiffness is materially non-linear (P-y curve) but for the small caisson head deflection most SE's are going to tolerate, a linearly elastic soil/rock spring is OK in my opinion. Doing material non-linear FEA based on a geotechnical parameters known to one or two significant figures is "putting lipstick on a pig".
Consider whether the TOP of your caisson is "fixed head" or "free head" and I usually model the caisson as having a cracked cross section (Ieff = 0.5 Igross) as a simplification.
The soil stiffness immediately at the top of the pier, the depth of overburden and the pier head BC's affect forces and deflections for laterally loaded piers MUCH more so than the bedrock penetration is my experience.
RE: Required rock socket embedment for Caissons (to develop fixity)?
RE: Required rock socket embedment for Caissons (to develop fixity)?
RE: Required rock socket embedment for Caissons (to develop fixity)?
Also nearly every geotech report I've seen says to ignore the top 5' or so of rock due to it either being weathered or to account for spoilage due to drilling.
I've also analyzed several signs on drilled shaft foundation and found similar results.