Pipe Pile Foundation next to Existing Eco-Block Wall

Wandering Wallaby · Jul 18, 2022

Hi all, I’ve got a situation where there is an existing 12’ tall ecoblock wall about 2’ away from a daylight basement house. The wall was reinforced with geogrid which will now need to be cut away for the new structure. The Geotech is aware of this and is reinforcing the wall with piles and/or whalers. Their soils report also recommended using pipe piles on the structure so that is what I have designed.

Please see the attached sketches and photos.

At the uphill front side of the house there doesn’t seem to be a problem with the structure as long as the Geotech reinforces that wall from peeling away now that it doesn’t have sufficient geogrid layers. I’m not worried about sliding since the soil is pushing the wall inward against the basement slab. The slab is a structural slab spanning to grade beams and pipe piles that extend below the ecoblock wall. Would it be advisable to pin the slab at this location in case the adjacent wall were to ever fail?

However, on the downhill rear side (the daylight or walkout basement side) the basement slab is about 4’ above the top of the ecoblock wall, therefore I am worried about sliding at this location. To mitigate that, I have included slab dowels to pin the wall at the top.

This is in a wet and high seismic zone D. The majority of my projects do not require piles so I am not an expert on using them. Do any of you see any potential problems with my sketches or is there something that I am overlooking? I can provide more information if necessary.

Thank you,

PEinc · Jul 18, 2022

If there is any tension force on the piles, you will need to have connections of the piles to the footing with proper reinforcing steel. Your sketch currently shows the tops of the helical(?) piles in unreinforced concrete, below the bottom mat.

http://www.PeirceEngineering.com

SlideRuleEra · Jul 19, 2022

Wandering Wallaby said:
This is in a wet and high seismic zone D.

Please see my comments below this marked up image:

Excavation will have (some of) the existing wall "looming" over the work area. See that it is braced adequately to prevent collapse. IMHO, bracing can, and should be part of the Contractor's means-and-methods, you don't have to design it. However, I would require the Contractor submit his plan (not necessarily prepared by a PE), before excavation starts, for your review.

Batter piling may be difficult to install because the existing wall may (and likely will) interfere with the installation.
In high seismic conditions, batter piling can fracture a improperly designed pile cap or overload the pile when the horizontal seismic force puts the pile into extreme compression.
If you decide to use batter piling, specify the the batter (such as, 6 Vertical: 1 Horizontal). You don't want to have a design that relies on a certain batter, but let the Contractor guess what that batter should be.

Keep the design as simple and easy to construct as possible. In wet conditions a Contractor need to "get in & get out" of an excavation without wasting time on some intricate detail. (Note: I do not see any intricate details in your design... very good.)

Wandering Wallaby · Jul 19, 2022

Thank you both for the feedback.

I will definitely add a bracing note as well as take a look through my calculations and verify that I can use plumb piles at this location, and that none of them are in tension.

I really appreciate your time.

Thanks,

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Pipe Pile Foundation next to Existing Eco-Block Wall

Wandering Wallaby

Structural

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