secant pile wall - shear capacity in concrete "lagging"
secant pile wall - shear capacity in concrete "lagging"
(OP)
I am tasked with trying to make a secant pile wall work for a contractor.
The contractor wishes to use 36" diameter piles. The primary piles will be concrete mix with f'c = 1000. The secondary piles will have f'c = 4000 psi with a large W section embedded. Like all contractors, he wants to pinch pennies, so he's trying to push the center to center spacing as large as possible. Due to driving tolerances, this could result in very little overlap between primary and secondary piles.
Everything I have read and researches talks about the primary pile acting as lagging, which I can see. But, I have yet to come across information that specifies how to design it or check its capacity. ACI 318 (2002) has some language in section R22.5.4 talking about shear flow in plain concrete which I think could apply to this situation. However, there seems to be a lot of room for interpretation.
So, I wanted to check with the forum to see if anyone had experience with this and how best to handle it.
Thanks.
The contractor wishes to use 36" diameter piles. The primary piles will be concrete mix with f'c = 1000. The secondary piles will have f'c = 4000 psi with a large W section embedded. Like all contractors, he wants to pinch pennies, so he's trying to push the center to center spacing as large as possible. Due to driving tolerances, this could result in very little overlap between primary and secondary piles.
Everything I have read and researches talks about the primary pile acting as lagging, which I can see. But, I have yet to come across information that specifies how to design it or check its capacity. ACI 318 (2002) has some language in section R22.5.4 talking about shear flow in plain concrete which I think could apply to this situation. However, there seems to be a lot of room for interpretation.
So, I wanted to check with the forum to see if anyone had experience with this and how best to handle it.
Thanks.






RE: secant pile wall - shear capacity in concrete "lagging"
RE: secant pile wall - shear capacity in concrete "lagging"
http://www.soilstructure.com/
RE: secant pile wall - shear capacity in concrete "lagging"
RE: secant pile wall - shear capacity in concrete "lagging"
http://www.soilstructure.com/
RE: secant pile wall - shear capacity in concrete "lagging"
RE: secant pile wall - shear capacity in concrete "lagging"
http://www.soilstructure.com/
RE: secant pile wall - shear capacity in concrete "lagging"
RE: secant pile wall - shear capacity in concrete "lagging"
RE: secant pile wall - shear capacity in concrete "lagging"
RE: secant pile wall - shear capacity in concrete "lagging"
the biggest question i have is how to handle the shear through the "lagging". if we check the shear through the "beam" as: phi*(4/3)*gamma*f'c*bw*d, what do i use for "d"?
in the sketch below, i show two different assumptions for "d". one assumes it's half the depth of the overlap area, whereas the other assumes it's the full depth of the overlap area. since the primary pile is installed first, it seems to me that i should only count half the depth because of the way the concrete will bear on the secondary pile. if the process were reversed, i think i could justify using the full depth.
thoughts?
RE: secant pile wall - shear capacity in concrete "lagging"
I think you have an arch instead of a beam, but if it was a shear failure it would be a little piece that would have to extend back to the back face of the pier. The failure surface shapes of Appendix D come to mind.
The soil will largely arch between the male piers anyway.
RE: secant pile wall - shear capacity in concrete "lagging"
which Appendix D are you referring to?
RE: secant pile wall - shear capacity in concrete "lagging"
What is the purpose of the secant wall? Does it need to act as a cutoff wall against water? If not, and the soils are suitable, you could get rid of the female piers and just use shotcrete as the lagging similar to a soil nail wall.
RE: secant pile wall - shear capacity in concrete "lagging"
the simple solution is to increase the pile size or decrease the pile spacing so that i can get the numbers to pencil out. of course, that means more $ for the contractor which he will not like.
RE: secant pile wall - shear capacity in concrete "lagging"
If the contractor wants to stretch things out, make sure you are not on the hook if it leaks worse than expected.
RE: secant pile wall - shear capacity in concrete "lagging"
RE: secant pile wall - shear capacity in concrete "lagging"
In general I agree it is an arch, but I think there comes a point where the overlap gets small enough that shear becomes an issue.
RE: secant pile wall - shear capacity in concrete "lagging"
RE: secant pile wall - shear capacity in concrete "lagging"
RE: secant pile wall - shear capacity in concrete "lagging"
Would you mind sharing your calculations for reference?
RE: secant pile wall - shear capacity in concrete "lagging"
RE: secant pile wall - shear capacity in concrete "lagging"
RE: secant pile wall - shear capacity in concrete "lagging"
RE: secant pile wall - shear capacity in concrete "lagging"
RE: secant pile wall - shear capacity in concrete "lagging"
the primary pile is the one installed first and is typically the one without reinforcing/steel piles. the secondary pile is installed second.
it makes sense when you picture a rebar cage being placed in the shaft. if the rebar cage was installed first, you wouldn't be able to cut the overlapping pile through the cage.
RE: secant pile wall - shear capacity in concrete "lagging"
I agree with slickdeals as to the terminology.
The order of installation is not what makes a pile primary or secondary. Rather, it is their function which determines this, and the reinforced ones are primary.
The piles installed first, using low strength concrete, are generally called 'soft' or 'female' piles.
The piles which are reinforced, either by structural steel or reinforcement bars, are called 'hard' or 'male' piles.
RE: secant pile wall - shear capacity in concrete "lagging"
scroll down to figure 3.14.
RE: secant pile wall - shear capacity in concrete "lagging"
In Southern Hemisphere (roughly; Nobody go and get roudy on me!) Hokkie is entirely correct... Primary and Secondary carry their names by FUNCTION.
In the USA and SOME parts of Canada (I do not know Continental & East European practice well enough to comment) the naming is by ORDER of INSTALLATION.
You're both correct. You're also both fine persons, even if one is a man or honour and the other must be satisfied merely with his honor.
RE: secant pile wall - shear capacity in concrete "lagging"
RE: secant pile wall - shear capacity in concrete "lagging"
I'd certainly vote for naming by function. Just makes more sense.
RE: secant pile wall - shear capacity in concrete "lagging"
...then Australia got smart and adopted the metric system so no more 4x2's