Passive Pressure Reduction 1

[InDepth]

Geotechnical Circular # 4 Appendix B lists the Wang-Reese equations for evaluating ultimate passive resistance for embedded beams.

See attached.

Does anyone have any references to a case where a caisson is drilled into the passive zone wedge (as in a drill hole next to a soldier pile)? Is there a critical distance between the soldier pile and the drilled caisson where the drilled hole collapses? What failure modes are introduced and how do you calculate the ultimate passive resistance?

Looked into casing and pre-drilling the caisson holes before excavation, but wanted to know if I could avoid this. Also realize that I can brace the bottom of the pile and not count on passive pressure....except I think it's impossible for cantilevered soldier piles.

 

[PEinc]

I don't know of a reference for this reduction. However, I always make sure that I locate my soldier beams so that the caissons are located mid-way between the soldier beams, in front of the lagging, not the soldier beams. I never had a problem as long as I placed the soldier beams away from the caissons. This can lead to some odd soldier beam spacings along the sheeting wall. If this is not possible, then the caissons have to be drill first or the upper portion of the caisson drill holes need to be tightly cased with a steel pipe.

 

[InDepth]

Thanks PEinc. Something like this sequencing (see attached) but with shoring piles offset from structural piles and casing option?

Odd soldier pile spacings is what I'm having to deal with, not to mention underground obstructions (existing piles and utilities) which shift the soldier piles, so in some cases I'm forced to have a new structural pile drilled next to shoring.

 

[PEinc]

If field conditions make it necessary to drill in front of soldier beam #8, you can sometimes weld beam seats on soldier beams #7 and #9 and then span a beam between #7 & #9. Then, you weld another seat or bracket to #8, above the spanning beam. This beam can prevent #8 from dropping and or moving toward the drill hole. This can work for isolated soldier beams but not for a run of several consecutive soldier beams.

 

[InDepth]

Realized I attached the wrong document on the second post.