HELICAL PIERS finding worse case allowable for axial loads
HELICAL PIERS finding worse case allowable for axial loads
(OP)
Given a soils report that states use end bearing capacity of 10,000psf for 15' depth take that time 8" shaft area and find 3360 lbs divide by 0.5 from equation 18-4 ibc 2009 this is the Pa allowable axial design load? Contractor uses chance piers the show a allowable of 36.7kips from using cohesian and muliplyer of Nc = 9 with blow count of 86? total loads on piers are around 10000lbs two story concrete basement wall with brick veener. am I missing something ?






RE: HELICAL PIERS finding worse case allowable for axial loads
RE: HELICAL PIERS finding worse case allowable for axial loads
Do you mean 8" diameter shaft?
Typically helical anchors use between 8 to 14 inch diameter plates and sometimes use multiple plates.
I'm not sure you can equate an allowable bearing pressure from a soils report for end bearing with the pile capacities developed by helical piling.
(If the 10,000 psf is an allowable pressure - not sure you take another 0.5 factor on it as typically allowable pressures already have safety factors of 2 or 3 depending on soil)
RE: HELICAL PIERS finding worse case allowable for axial loads
RE: HELICAL PIERS finding worse case allowable for axial loads
RE: HELICAL PIERS finding worse case allowable for axial loads
RE: HELICAL PIERS finding worse case allowable for axial loads
Thus, the helical pile company is required to provide certification or warranty that their product will perform - (i.e. provide x kips of capacity) with a designated safety factor.
I also wonder if 15 feet of depth is not what you'll end up with as many times helical piling go as deep as necessary to develop the required axial capacity.
RE: HELICAL PIERS finding worse case allowable for axial loads
RE: HELICAL PIERS finding worse case allowable for axial loads
RE: HELICAL PIERS finding worse case allowable for axial loads
Basically for non-cohesive soils, if you have an effective friction angle of the soil you can find "Nq" for your non-cohesive bearing factor then multiply this by the overburden pressure. So basically they are using the ultimate bearing capacity and then applying a suggested safety factor, usually 1.5 - 2.0.
For cohesive soils Nc=9 is recommended.
cohesion = c=N/8 where N = blow count. However this is given as an estimate, it is recommended other means be used to determine cohesion.
Bearing = Q = Area * c * Nc
EIT
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