H Pile and Lagging 2

[hawkaz]

Project: New addition with a basement going in next to an existing at grade commercial building.

To retain the soil/footing for the existing building, we are considering H piles and wood lagging next to the existing footings, then put a new concrete wall on the basement side once we get deep enough.
What happens when the lagging eventually deteriorates- is there a risk of the existing building settling?

What other options have people used for lagging in conditions like this?

Thanks

 

[jayrod12]

Around here the lagging gets pulled once the new wall is in place, cured and braced. Then it is backfilled. Alternatively, why not look at a tangent pile wall that can act as your basement wall after the fact?

 

[hawkaz]

Thanks Jayrod
A tangent pile wall was my other suggestion to the GC- but they would prefer H piles.

Unfortunately, due to the proximity of the existing building we are building next to (we are right up against the existing footings), whatever we install will need to remain in place. They will not be able to get access to the lagging to remove it

 

[jayrod12]

There are many other smarter fellows here than me that might rip this to shreds or have a better solution, but if I was forced to go this way (I would be fighting tooth and nail against it) then I would be requiring PWF lagging (not your standard P.T. wood but something intended to be in the ground forever), I would also still be trying to remove the top few pieces of lagging and providing a solid clay cap on the top.

Have you ever pulled old wooden fence posts out of the ground? They're rarely rotten more than 12" into the ground, the rest is typically in perfect shape. It's not necessarily the embedding in the ground that causes issues, it's the constant wetting and drying and being exposed to the air. So if you could get heavily treated lagging with a good clay cap on top, the deterioration may not be as bad as expected.

 

[hawkaz]

Good idea- Thanks

 

[PEinc]

How close will the H-Pile & lagging wall be to the existing building? Sheeting walls are generally flexible support systems and, as such, are not recommended for supporting buildings. Consider whether you need to underpin the building.

http://www.PeirceEngineering.com

 

[hawkaz]

Thanks for the suggestions

Unfortunately, we will be as tight as possible to the existing building footings. We will be using the for retaining only- the building support structure will be independent.
Underpinning would be be a challenge for two reasons- 1. Our new basement slab will be 6 feet or so below bottom of existing footing and 2. The existing building will be occupied during construction.

The elevations would be a challenge, but we could make it work. I don't think I want to risk this with the building being occupied however.

 

[Durtguy]

Had a similar project near a pumping station that required the lagging to stay in place. Somewhat expensive but used the sides of trench boxes. They stayed in place and solved that problem. Trench guys will often resell older boxes which work well for the lagging you are looking for.

PS. You also know the bending and deflection capacity of the sections with respect to equivalent fluid pressures.

Good Luck.

Durtguy

 

[PEinc]

hawkaz, you said, "Underpinning would be be a challenge for two reasons- 1. Our new basement slab will be 6 feet or so below bottom of existing footing and 2. The existing building will be occupied during construction."
Neither of these two reasons should be a problem for underpinning. Six feet deep underpinning is rather shallow and may not require any lateral support. Most buildings being underpinned are occupied.

http://www.PeirceEngineering.com