Basement walls vs. Retaining Walls
Basement walls vs. Retaining Walls
(OP)
I've spent the last couple of years working on residences with relatively shallow basements, stem walls usually not more than two to four feet in height. I'm now working in an area where uneven terrain seems to be the norm or at least more likely. I've seen some stem walls designed in these situations with unbalanced fill, designed as retaining walls. I'm looking for more examples of this type of situation where you have a stem wall exceeding 4ft in height with unbalanced fill. What is a typical retaining/stem wall design? What factors are at play? And what things should I look out for?
With a typical basement wall the interior slab will provide some lateral restraint or at least that is my understanding. I'm also looking for any good resources on foundation and basement design in general.
Another thing I've noted is that with post and beam foundations usually I see a designer use a 4x8 beam with 4x4 posts. With this new area I'm working in the designer likes to use 2x4 stud walls on a strip footing, rather than post and beams. I'm not saying this is wrong but I'm curious to what the pros and cons are from an engineering perspective.
With a typical basement wall the interior slab will provide some lateral restraint or at least that is my understanding. I'm also looking for any good resources on foundation and basement design in general.
Another thing I've noted is that with post and beam foundations usually I see a designer use a 4x8 beam with 4x4 posts. With this new area I'm working in the designer likes to use 2x4 stud walls on a strip footing, rather than post and beams. I'm not saying this is wrong but I'm curious to what the pros and cons are from an engineering perspective.
A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com





RE: Basement walls vs. Retaining Walls
You already have this (Link), right? If so, I'm pretty sure that it covers basement wall design.
Usually 8" thick. Residential contractors push for unreinforced walls and sometimes they get them per prescriptive code requirements. If your market will tolerate it, try to get one mat of rebar on the inside face of the all. #5 bars are smaller is pretty residential friendly.
You may need to deal with:
1) Hydro-static pressure depending on the water table and drainage strategy.
2) At rest earth pressures.
3) Surchage due to vehicular traffic etc.
4) Seismic load of the soil being tossed against the wall.
5) Delivering the reaction from the top of the walls into the floor deck can be challenging. Tough connections and heavily taxed diaphragms. Some situations lead designers into using cantilevered retaining walls rather than propped walls. That can get expensive however.
Not sure I understand this. Where you've got a wall there anyway, efficiency would seem to dictate using that wall for support of gravity loads.
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.
RE: Basement walls vs. Retaining 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.
RE: Basement walls vs. Retaining Walls
Thank-you for your detail response KootK. I've done some reading on retaining walls a few months back and the vehicular traffic was one thing that jumped out at me. I'm wondering though if it is customary to design for long term traffic versus construction traffic, or maybe it is more conservative to consider the worst case scenario (ie. fully loaded concrete truck etc...)
A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com
RE: Basement walls vs. Retaining Walls
1) No surcharge at all.
2) Surcharge equivalent to two more feet of soil. That's roughly on par with densely parked cars or humans.
The attached document has some excellent information on the wall to floor deck connections.
Another thing to watch out for is areas where you don't have a diaphragm to connect the top of the wall too. It occurs quite often where stairwells abut the building perimeter.
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.
RE: Basement walls vs. Retaining Walls
A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com
RE: Basement walls vs. Retaining 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.
RE: Basement walls vs. Retaining Walls
A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com
RE: Basement walls vs. Retaining Walls
1) Having no toe at all causes severe joint detailing issues. Whenever possible, I provide enough toe that I can get all the bars properly developed etc.
2) Some situations, such as zero lot line, require zero/limited heel for project specific reasons.
3) Zero heel retaining walls often do reduce excavation quantities. And it's tough to sort out the economics in a way that applies to all situations. For example, I've had numerous contractors express a preference for using heel-less retaining walls either side of driveways into basements. There, sliding issues can be overcome by connecting the two sides across the drive lane.
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.
RE: Basement walls vs. Retaining Walls
On the pony wall retaining wall the contractor wants the size of the toe and heel reversed since the wall might be near a property line and does not want the heel to project further than necessary.
A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com
RE: Basement walls vs. Retaining 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.
RE: Basement walls vs. Retaining Walls
A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com
RE: Basement walls vs. Retaining Walls
For your large toe, small heel wall, can sliding not be resisted by the SOG? You could add a key but you'll likely hear some contractor whining about that.
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.
RE: Basement walls vs. Retaining Walls
A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com
RE: Basement walls vs. Retaining Walls
A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com
RE: Basement walls vs. Retaining 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.
RE: Basement walls vs. Retaining Walls
I've tried to make a retaining wall work with similar dimensions to those shown with a 18" heel and an approx. 36" toe. No matter what I do the Sliding FS is less than 1.5 , the only way to get this to work is to either add a key or have a basement slab, otherwise it is a "no go". Please let me know if I missing something here, the contractor wants a small heel but I don't think its possible.
With a 6' high retained height and a toe of 3 ft, heel of 2 ft, I get a sliding FS of 1.19 (Soil Friction 0.35), even if I up the friction to 0.4 I'm still at 1.33 on the sliding FS.
A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com
RE: Basement walls vs. Retaining 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.
RE: Basement walls vs. Retaining Walls
A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com
RE: Basement walls vs. Retaining 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.
RE: Basement walls vs. Retaining Walls
That was the next thought that ocurred to me, increase the footing depth and hence its self weight and also its lateral surface area.
I'm still not entirely clear on the change in the reinforcement from heel to toe, most of the other thread goes over my head at this point, I am waiting to get the book you recommended to further immerse myself in retaining wall design. The whole strut-tie thing is something I'm not familiar with.
A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com
RE: Basement walls vs. Retaining Walls
Nonsense. Strut and tie = truss = medeek. You're like the international ambassador of trusses these days.
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.