what concrete strength is high enough when considering the lateral resistance of a cantilevered soldier pile and lagging yet low enough so soldier piles can be removed from their caissons with a backhoe? I am trying to see how much steel can be salvaged I am thinking of 500 psi is a happy medium, any thoughts on this?
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salvage soldier pile from its caisson
- Thread starter EngMan40
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I routinely call for f'[sub]c[/sub] = 100 psi for backfilling soldier beam drill holes. 500 psi is more than you really need, unless required by specs.
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- #3
PEinc, with this low strength, wouldn't this material crack in front and to the sides of the soldier piles and, therefore, would you still consider the 3 caisson diameters arching of the passive? I did Lpile run once with low strength concrete and it won't converge...
I use 100 psi all the time without problems. FHWA calls for backfilling the soldier beams with low strength concrete or flowable fill with a compressive strength of 0.35 MPa which is only 51 psi. I do use 3b for the passive resistance (unless soft or loose soil), but I do not design for a composite concrete/steel beam in the embedded length. The beams supports the loads.
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- #5
the moment at dredge line is less than maximum moment occurring below it and designing steel beam for the moment at dredge line will yield more economical section than that using the maximum moment. A composite caisson/steel section capacity using, say 2,000 psi, concrete will result in much higher capacity to handle the maximum moment than steel itself. I am not sure if you consider deflection in your calcs
For a cantilevered soldier beam in soil, the maximum moment is always below the bottom of the excavation. You may be making this more complicated than necessary or usual. Just pick the right size soldier beam to resist the maximum bending moment and minimize beam deflection. For a relatively low, cantilevered soldier beam wall, it should be cheaper to upsize the soldier beam than to build a composite concrete & steel embedded length; not to mention that, if you pour too much structural concrete in the embedded length below subgrade, you may have to chip it out later to install lagging.
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