(Hopefully) Simple Drilled Pier Question
(Hopefully) Simple Drilled Pier Question
(OP)
I am not sure if this is the correct area or not but here goes:
I will be putting in some drilled piers (caissons, whatever you want to call them) that are about 5' to 11' in diameter and 9' to 27' in depth. The question is if they will need to be installed using slurry. The question I have personally for my own personal education is which is more important in trying to decide how well the hole will hold up, the PI or the Blow Count. Also, is there any kind of quick rule of thumb to determine the vertical stability of the hole using those vales since they are typically included in the boring logs for geotech reports.
On a side note, this project is broken up into 2 phases and thus has two geotech investigations. The problem is that the northern half of the project was completed by one company and the southern by another company. At the mid point of the project both companies had bore locations that were close to each other, relavitely speaking. The issue is that both companies came up with different results. While there is certainly the possibility of a geologic change between the north section and the south section, I find it suspicious that the change occurred right at the point of handover from one company to the next.
Anyways, any help would be appreciated.
I will be putting in some drilled piers (caissons, whatever you want to call them) that are about 5' to 11' in diameter and 9' to 27' in depth. The question is if they will need to be installed using slurry. The question I have personally for my own personal education is which is more important in trying to decide how well the hole will hold up, the PI or the Blow Count. Also, is there any kind of quick rule of thumb to determine the vertical stability of the hole using those vales since they are typically included in the boring logs for geotech reports.
On a side note, this project is broken up into 2 phases and thus has two geotech investigations. The problem is that the northern half of the project was completed by one company and the southern by another company. At the mid point of the project both companies had bore locations that were close to each other, relavitely speaking. The issue is that both companies came up with different results. While there is certainly the possibility of a geologic change between the north section and the south section, I find it suspicious that the change occurred right at the point of handover from one company to the next.
Anyways, any help would be appreciated.





RE: (Hopefully) Simple Drilled Pier Question
P.I. is better indicator of how well the drilled shaft will stay open. As a rule of thumb, P.I. value greater than 10 means the soils have substantial amount of clay like particles. Also, look at the boring logs and look for "qu" or unconfined compressive strength value of 1.5 TSF or greater.
RE: (Hopefully) Simple Drilled Pier Question
As for standup time, the earlier advice is reasonable. Depends a lot on the nature of the material deposition/degradation (varved clays, for example), previous stress histories (slickensided zones). You might wish to speak with a couple of drilled shaft contractors in your area and find out how they have done this before in the same general vicinity. There experience is probably more valuable than from those of us who don't have the local knowledge.
RE: (Hopefully) Simple Drilled Pier Question
I'd suspect any move in the direction of stabilizing the hole with a fluid will be an on-site decision in marginal areas, between obviously bad conditions vs. stable materials. It sure is a lot more complicated an operation and to be avoided where possible.