LetsTalkEng
Structural
- Mar 27, 2018
- 2
Hello Everyone,
I've come across an interesting existing exterior foundation wall condition and have begun exploring the use of EPS Geofoam as a solution. At a high level I have having difficulty finding the appropriate design parameters, but wonder if it's because I am not asking the right questions. A brief discussion of my condition/problem below.
Existing Condition:
Exterior 12" concrete foundation wall r/w 15M @ 16"c/c each way each face, Running E-W. Typically 10'-0" tall, fully back filled. Floor framing is steel beams with 2 1/2" topping on 1 1/2" metal deck floor framing on the South side. 15' from the West end the basement slab depresses for a theater room. This condition extends 24' until it meets a return wall from the North. Further east of that is an underground garage where the wall is not back-filled on either side. North of the theater room wall, planters are proposed with 4'-0" of planting medium. A contextual section with assumptions is attached.
Now, if that foundation wall get's back filled full height, the loading will be over double what it is capable of sustaining. What I am proposing is to backfill to approximately 3' from t/o basement slab to cover the exterior weeping tip and drainage. From there I will have a geotechnical consultant specify a berm slope extending North and likely West, to prevent any at rest earth pressures and create slope stability. I'll fill this sloped area in with EPS geofoam to 4' below final grade. The final 4' would then be filled with planting soil. My general understanding is that I then have Ko soil pressures from soil + surcharge from at grade down to 4'. The geofoam then transfers the vertical load down to the soil located 3' above t/o slab, where the same Soil+surcharge theory applies.
Why question is what happens across the depth of the geofoam? It can take the vertical stress, but there will be some component in the lateral direction as well. Based on leafing through a few papers, I can loosely calculate Ko using the Poisson's Ratio of the geofoam using Ko = v/(1-v); v=0.15 for mist EPS I have seen. Then I'd use a similar methodology to develop my lateral pressures across this depth as well. I've reached out to EPS suppliers, and although they agree Geofoam is a great option, nobody has committed to providing any kind of design criteria. In addition, the project is not in a seismic region, so the use of Geofoam is foreign territory to the geotchnical consultants as well who have only surmised that I should use the supplier's recommendations, thus taking me full circle.
Looking for any insights or considerations I might be overlooking from suppliers/engineers whom are likely more well versed in the use of Geofoam. Thanks in advance!
Cheers,
LetsTalkEng
I've come across an interesting existing exterior foundation wall condition and have begun exploring the use of EPS Geofoam as a solution. At a high level I have having difficulty finding the appropriate design parameters, but wonder if it's because I am not asking the right questions. A brief discussion of my condition/problem below.
Existing Condition:
Exterior 12" concrete foundation wall r/w 15M @ 16"c/c each way each face, Running E-W. Typically 10'-0" tall, fully back filled. Floor framing is steel beams with 2 1/2" topping on 1 1/2" metal deck floor framing on the South side. 15' from the West end the basement slab depresses for a theater room. This condition extends 24' until it meets a return wall from the North. Further east of that is an underground garage where the wall is not back-filled on either side. North of the theater room wall, planters are proposed with 4'-0" of planting medium. A contextual section with assumptions is attached.
Now, if that foundation wall get's back filled full height, the loading will be over double what it is capable of sustaining. What I am proposing is to backfill to approximately 3' from t/o basement slab to cover the exterior weeping tip and drainage. From there I will have a geotechnical consultant specify a berm slope extending North and likely West, to prevent any at rest earth pressures and create slope stability. I'll fill this sloped area in with EPS geofoam to 4' below final grade. The final 4' would then be filled with planting soil. My general understanding is that I then have Ko soil pressures from soil + surcharge from at grade down to 4'. The geofoam then transfers the vertical load down to the soil located 3' above t/o slab, where the same Soil+surcharge theory applies.
Why question is what happens across the depth of the geofoam? It can take the vertical stress, but there will be some component in the lateral direction as well. Based on leafing through a few papers, I can loosely calculate Ko using the Poisson's Ratio of the geofoam using Ko = v/(1-v); v=0.15 for mist EPS I have seen. Then I'd use a similar methodology to develop my lateral pressures across this depth as well. I've reached out to EPS suppliers, and although they agree Geofoam is a great option, nobody has committed to providing any kind of design criteria. In addition, the project is not in a seismic region, so the use of Geofoam is foreign territory to the geotchnical consultants as well who have only surmised that I should use the supplier's recommendations, thus taking me full circle.
Looking for any insights or considerations I might be overlooking from suppliers/engineers whom are likely more well versed in the use of Geofoam. Thanks in advance!
Cheers,
LetsTalkEng
