I would appreciate it if someone could provide me a reference with figures showing the influence zone of friction bored pile socketed in rock. Thank you.
The title of your post begs the question. How is this bored pile, also known as a drilled shaft, developing capacity? Is all of the capacity in the rock? If so, the influence zone will be fairly small. If you are also developing capacity in the soil, have you checked strain compatibility? So many questions and ways for this to go sideways.
What is the center to center spacing of the piles? Have you check the overall group effects, i.e. treated all of the piles in a single cap as a single foundation element?
Thank you for all the reply and r13 for the link.
I read a manual "Pile Design and Construction Practice by Tomlinson". stated:
“The length to diameter ratio of the rock socket is an important factor in the consideration of the bearing capacity of the pile in shaft friction and there is no point in adopting a length greater than that required to develop full available resistance. The distribution of sidewall shear stress (rock socket skin friction) for various length to shaft ratios (see Figure 7.18). It will be seen that the ratio should be less than four if it is desired to mobilize base resistance in addition to socket resistance. The higher interface stress over the upper part of the socket will be noted.”
This means that if L/D > 4 the influence zone at the tip of the pile socketed in the rock is minimal.
Currently, we have a project a high rise building and is located in an area that from ground level to -9m is unsuitable soil, -10m to -17m different layers of weak rock (calcilutite and calcisiltite) and -17m to below is limestone/aquifer.
One foundation system proposal is a bored pile socketed in rock with 2 meters buffer from the level of limestone/aquifer. One of the requirements is not to damage or puncture the aquifer.
