Increase in soil height with a cast in place basement wall 1

[clemsonCMT]

I have searched the posts and have not seemed to find one similar to this so I will give it a shot. I have a client working on an existing hospital in SC. The hospital is being renovated and the existing grade adjacent to the basement walls needs to be raised approximately 5 feet. I am currently trying to figure out the increase in pressure along the face of the wall and what my options are for raising the grade. Removing the wall is not an option and reinforcing the wall further may not be either. Ineed to come up with a solution for raising the grade without increases the pressure on the wall. No design/specifics are available as to the construction of the basement wall. I figure if I do not increase the current condition then we would be safe.

The basement wall is 16 tall and backfilled with 11' of soil. I do not know the specifics on the soil type. I am assuming a combination of a clayey silt, silty clay being that those are the majority of the soils located here. The grade needs to be raised 5' in around this basement.

Doing some preliminary calculations I have used the at rest condition and solved the pressure per foot along the wall with Po=.5[ko(gamma ')H]H. Is my assumption right the wall is at an at rest condition. My calculations came to 3,620 #/ft for the existing condition with 11' of soil backfill.

Scenario 1: Raise the wall with soil assuming gamma' is 120 pcf. Po=7,680#/ft (No good)

Scenario 2: Remove the 11' of backfill soil and replace with 16' of 57 stone. Po=7,040. (No good)

Scenario 3: Remove 11' of backfill and replace with 16' of lightweight aggregate (SOLITE)
Po=4,800#/ft (No good)

Foam was also brought up but the cost seems way too high.

Any suggestions/alternatives would be greatly appreciated. I have not been on here long, but I really enjoy reading the posts and replys. Very imformative.

 

[msquared48]

Depending on the type of wall you have, you may have more than one problem here. True, you have the wall itself with it's reinforcing, but you also have the footing to worry about - specifically, whether this is a yielding or non-yielding wall. The pressures on the wall are different, plus how the footing acts. The increase in the soil height could affect the soil pressure too.

Do you have any existing drawings on the wall and its foundation?

Mike McCann
McCann Engineering

 

[clemsonCMT]

i do not have any information on the existing basement wall. Which makes me nervous in the first place.

Jason Vaughn
smeinc.com

 

[msquared48]

Then you may need to do some on-site testing to include locating the rebar and coring/excavating to determine the size of the footing. This is critical to any plan for retrofit.

Mike McCann
McCann Engineering

 

[MSEMan]

Have you thought of excavating the existing fills and putting in a pressure relief wall?

See link for example:

http://www.earthteccorp.com/default.asp?contentID=25

Alternatively you could consider driving permanent sheet piles adjacent to the existing wall prior to filling but this may be expensive and there may be vibration issues depending on what equipment the hospital has installed in the basement.

Hope this helps.

 

[msquared48]

MSEMan:

Your link is not a bad idea if it is not too close to the property line. Skeptical about the sheet pile though.

Mike McCann
McCann Engineering

 

[fattdad]

I'm not sure why "Solite" wouldn't work. If you remove soil and replace it with something that has 69 percent of the original backfill density, you should be o.k. (i.e., 11/16=0.69). The only thing that changes is the location of the earth-pressure distribution, but the overall loading should remain the same.

You could also remove the soil and replace it using a mechanically-stabilized embankment with a wrapped face against the existing basement wall. This could essentially remove the earth pressure from the basement wall.

Just a few ideas to add to what's already been offerred. . . . . .

f-d

¡papá gordo ain’t no madre flaca!

 

[SEshore]

I'd install tiebacks through the basement wall. I've had success with this in underground parking garages. You'd use a limted access rig that can operate in low overhead conditions. The trick would be getting the rig into the basement.

 

[DarthSoilsGuy]

a similar situation on a retrofit to an old steel structure with exterior brick masonry walls which required converting a previously 1st floor building with windows into a basement.

The SE chose to trench and install a concrete wall that pinned between the footing and the 1st floor diaphragm. probably a more expensive option then you're looking for. you could also trench in a gravity wall if you can't pin it.

if you go with any washed stone options, make sure your drainage is done well.

The potential change in soil load path is the X-factor. Old buildings don't like new tricks and soils never went to college.

is SME branching out, or is this part of a prelim geotech report.

 

[clemsonCMT]

Nah we are not branching out, but we were requested to come up with some options for the retaining wall and raising the grade. I really appreciate the feedback posted and I am talking with one of our senior guys and I will post how it comes out.

I really like the idea of placing the mechanically-stabilized embankment with a wrapped face against the existing basement wall. Thanks fatdad.

Thanks to all for your replies.

 

[MSEMan]

Clemson,

be careful about the wrapped faces - they are really hard to build and if the contractor messes up you are totally up the creek. Ese a steel mesh face and for God's sake use good backfill!

 

[MSEMan]

Clemson,

be careful about the wrapped faces - they are really hard to build and if the contractor messes up you are totally up the creek. Use a steel mesh face and for God's sake use good backfill!

 

[fattdad]

Not sure about using a steel mesh. Tensar makes geogrid in HDPE or poly-something that would be immune to corrosion and durable.

I'm still thinking solite would work. . . . .

f-d

¡papá gordo ain’t no madre flaca!

 

[civilperson]

Build internal or external pilasters, (counterforts or buttresses) for additional wall bracing to match the added stress from the fill.