Soil Nail Wall?

[SteelPE]

I am looking at a project that requires some deep excavations next to an existing building. My client is expanding his business and wants to put an addition on that requires a basement. He wants to maximize his space, therefore, he wants to locate his basement as close to his original building as possible.

My question is to the use of a soil nail wall. Who is responsible for the design of this wall system, the structural engineer, the geotechnical engineer or is this something the contractor would typically do?

 

[dicksewerrat]

How deep is this basement? You may need steel sheets vibrated in.

Richard A. Cornelius, P.E.

http://WWW.amlinereast.com

 

[SteelPE]

The plans are still preliminary and the existing building SOG steps along the length of the addition so the depth of excavation varies from 12' to upwards of 24' (depending on where the addition stops).

 

[KootK]

In my area, it's done by an engineer working on behalf of a local shoring contractor. However, the EOR usually has the unenviable task of trying to figure out the details of the system well before the shoring contractor is engaged. I'm working on a similar problem at the moment for a four story basement. We call 'em diaphragm walls.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[SteelPE]

It seems like something that the contractor would handle.... Never worked on a job quite like this before.

 

[slickdeals]

Diaphragm walls are not the same as soil nail walls, which is different from a sheet piled wall.

 

[KootK]

Geotechnical terminology can be pretty inconsistent from one geographical location to the next. The system that I'm using will be a 6" shotcrete wall that will go down in 5' lengths. It will have tie-backs that will destress over time and vertical micropiles embedded within the wall. When all is said and done, the exterior of my foundation wall should be 150-200 mm from the exterior edge of the adjacent footings.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[PEinc]

Sheeting and soil nail walls are not the best ways to support an existing building. Sheeting is usually a flexible system, which can lead to settlement and lateral movement of the building. Soil nails are passive elements that need to stretch and move in order to pick up the tension loads. Vibrating SSP in place against a building can (will) cause problems. Soil nailing is NOT underpinning.
If the existing building will not be underpinned, then the new basement foundation wall needs to be designed for the surcharge load from the existing building. If the underpinning or other type of retaining wall is not a permanent wall with corrosion protection, then the new foundation wall also needs to also be designed for the lateral earth pressure.

http://www.PeirceEngineering.com

 

[PEinc]

Do an Internet search for "Building collapses on North Queen Street in Lancaster" Pennsylvania.
This was a job where soil nailing was designed to support an adjacent building instead of using underpinning. The building collapsed as soon as the first lift of excavation was made for the soil nail wall.

http://www.PeirceEngineering.com

 

[JedClampett]

Why restrict yourself to a soil nail, sheet pile or any one type of wall? Define your criteria (retain soil; no damage or settlement to adjacent properties, etc.), show your work area and let the contractor take the risk and provide the design. Soil nails, for instance, besides all the technical reasons stated above, might interfere with existing utilities. Unless this wall provides the permanent structural retaining wall, it's technically means and methods. You can review it or take a strictly hands off approach, it's up to you. While this is scary, some engineers design these all the time and contractors build them just as often.
But don't over proscribe this or it might be your turn in the barrel. I've done these (the contractor chose soil nails and shotcrete) and was scared ever minute the silly thing was up. But it worked.

 

[SteelPE]

Why limit myself...... Because this building was proposed to be built 10 years ago. The owner hired a company to start the design. When I met with him a few weeks ago he handed me a section showing a soil nail wall to shore up the existing building. It is unclear at this point (because I do not have the detail in front of me) if the wall is intended to support the building forever or if there is another wall in front of the soil nail wall that will support the final loads.

I will say that the existing building is a single story 10ft eave height metal building so the loads should not be that large. This is the third addition that he has done in similar fashion...... But with the SOG elevation change stabilization of the existing gets worse as we move down the building.

 

[Lion06]

In my neck of the woods this is a Means and Methods issue for the contractor to hire his own engineer to solve and the EOR to review. As the EOR, you have the final word as to what's acceptable and what isn't.

The way I was mentored is that we, as the EOR document what we want as the final condition (e.g. Basement wall next to adjacent building) and how the contractor gets there is his Means and Methods. Trying to dictate how the contractor builds will inevitably lead to discussions about the EOR costuming the job money because the contractor can come up with a better or faster method. With that said, it's incumbent upon the EOR to ensure that he believes there is a realistic way to build what he wants.

You should require in the spec and General Notes that shop drawings and calculations be submitted for review.

 

[darthsoilsguy2]

in my experience this has typically a design/build thing with the specialty contractor on the hook for liability provided you specify it to recognized standards especially the parts where you require them to prove their design assumptions by their load testing of anchors(FHWA has some good references). many of the design references were written by specialty contractors that may bid your job. However, if something bad happens... i assume that won't keep you out of the mess. i assume permission to put these anchors under the neighbor's property has been legally secured.

 

[SteelPE]

Permission is not required as the owner will be infringing on his own property. He is basically undermining his own building. Seems like a lot of money is going to be spend to place the basement but the owner does have other needs that are accomplished by adding the basement.

 

[dcarr82775]

This is almost always the specialty contractor's to design. Depending on the depth of cut, look at micropiers or smaller diameter drilled piers. If you use a cap beam and tie it into the s.o.g. at the top it could be economical, but probably falls to you to design instead of soil nails or other more temporary system.

 

[SteelPE]

dcarr,

So, would you be using the micropiers at the top of the wall to resist the lateral loads produced by the unbalanced soils.... sort of a "propped" retaining wall?

This will be the second addition they have done in a similar fashion. I believe they said they used sheet piling while constructing the last addition. However, only 8'-10' of undermining/underpinning was required. They also reverenced "dead men" that were installed inside the existing building. I was too busy looking at other items in the building to hear if the dead men had been installed during construction of the addition.

 

[jayrod12]

Although I agree that this is something the specialty contractor will provide (i.e. he'll hire his own engineer to design the shoring). Please at least look at the feasibility of shoring prior to writing designed by others.

I've had to design shoring a few times, a couple times you could tell the EOR thought about the shoring first and the design was easy, there was enough room to install shoring. Everything was seamless on those jobs. The other jobs the EOR just wrote shoring by others without giving a second thought to whether it was possible or not. Those jobs were friggen headaches to no end. One of them in fact we never arrived at a feasible shoring solution (24' excavation with no room for rakers and deadman, and no allowance to put in soil anchors).

 

[dcarr82775]

It depends on the depth of cut, but yes. The piers wouldn't cantilever, they could be modeled as 'fixed' at their base and pinned at the top. A cap beam tied into the s.o.g. or deadmen would work. Micropiers can't do much on their own so it might need to be smaller drilled piers. That being said, if they used sheetpile before, it might be feasible to just use it again.

 

[SteelPE]

dcarr,

They use sheet piles before when the depth of excavation was only 12' (8' below bottom of footing). Now their excavation will be 24' (20' below bottom of footing). Slightly different than what was used before.

 

[dcarr82775]

Never mind, do not use minipiers for that range of depth. The same concepts could be used to reduce the size of sheet piling or soldier beams. I have seen a hybrid soil nail system used where the nails are really tensioned ground anchors. It helps to reduce movements a little. Definitely getting into a specialty contractor's realm.