How Far Back to Hold Building
How Far Back to Hold Building
(OP)
If there is a building proposed to be built on the fill side of a newly proposed cast-in-place concrete contilevered retaining wall, how far back from the back side of the wall would the building need to be held to not load the proposed retaining wall?
The wall retains 9' of soil and the grade behind the wall is level.
The bottom of footing of the proposed building, located on the fill side of the retaining wall, is 2'-4" below grade, thus the distance from the bottom of the proposed building footing to the top of the proposed retaining wall footing is 6'-8".
The proposed building is a brick clad, wood framed, two story townhome building.
Thanks for taking the time to render an opinion!
The wall retains 9' of soil and the grade behind the wall is level.
The bottom of footing of the proposed building, located on the fill side of the retaining wall, is 2'-4" below grade, thus the distance from the bottom of the proposed building footing to the top of the proposed retaining wall footing is 6'-8".
The proposed building is a brick clad, wood framed, two story townhome building.
Thanks for taking the time to render an opinion!





RE: How Far Back to Hold Building
Mike McCann
MMC Engineering
http://mmcengineering.tripod.com
RE: How Far Back to Hold Building
http://www.slideruleera.net/Steel-Piling.html
See page 16, for line loading apply a surcharge to retaining walls. I would think somewhere in the range of twice the distance away from the height of the wall the surchage loading becomes fairly insignificant.
The question comes though, if this is both a newly proposed wall and a newly proposed residence -- why not just design the wall for the surcharge loading?
RE: How Far Back to Hold Building
The soil retained by the cantilevered retaining wall probably would helps confine the soil that the proposed building will be founded upon, if the building was too close to the proposed wall, and because of that, I wanted to be sure I had the architect set his building back far enough away from the retaining wall so that my retaining wall is not laterally loaded by the proposed building weight.
While I was thinking about overturning, sliding of the proposed retaining wall has my attention too!
RE: How Far Back to Hold Building
I'm assuming the architect wants to probably utilize as much space as he can within setback requirements for the house (unless this is a really large lot).
It's not uncommon to apply surcharge loading to a retaining wall (i.e. think partial basement) and it's something that can be designed pretty easily.
RE: How Far Back to Hold Building
Actually, my architect has a great deal of space to place these buildings.
This architect is pretty darn knowledgeable. He and I discussed this project at length the other day. I told him I could design the wall for the surcharge, or, he could place the buildings far enough back from the wall to where we do not have to worry about surcharge. He wants some area between the wall and face of building anyway, so that folks can have a little yard right there. Also, given the high visibility of this retaining wall (parallel to a road) he told me he wanted me to go with the most conservative approach. I told him that would mean to move the building back, away from the wall, until it no longer would load the proposed wall. He likes that idea and wants me to tell him how far back to place the building.
I agree with you jdg....we need to use our space as best we can, but in this instance, my client wants to be outside of the area that would load this wall.
Seems like, from what I can gather from your previous post, If we place the building (2) x (6'-8") back from the back face of wall (13'-4") then the building is outside the area of loading this wall.
RE: How Far Back to Hold Building
RE: How Far Back to Hold Building
The second, the affect of the wall on the building. Retaining walls are generally designed and built around active earth pressures. To develop active earth pressures, the wall must rotate (deflect). When the wall deflects the soil backfill will move, some of this movement will be vertical and some will be horizontal.
For these reasons, I would not want my building with the a 1:1 slope from the back bottom of the retaining wall to intersect any portion of the footing.
Mike Lambert
RE: How Far Back to Hold Building
RE: How Far Back to Hold Building
Will it happen after backfill and before the building is constructed? Who knows. Depends on how much time occurs and the type of soil.
If granular soil, my be ok. If clay, maybe not.
Mike Lambert
RE: How Far Back to Hold Building
Where I practice in California our Geotechs typically require granular soil to be used as the backfill. Site soil can only be used per approval from the Geotech.
RE: How Far Back to Hold Building
RE: How Far Back to Hold Building
RE: How Far Back to Hold Building
Ron - To add to JDG's comment, if the backfill soil was slightly more cohesive than granular fill, I'm assuming the angle of influence to the adjacent building footing would be steeper?
RE: How Far Back to Hold Building
If the building is beyond this active wedge there should be limited influence on the retaining wall. This is not completely true, but close. You'd have to do a Coulomb construction based on the loading of the building as the actual building loads will affect the stresses acting on the Rankine failure plane.
If you are considering elastic conditions and you want to know how far back the building should be to limit any stress from acting on the retainign wall, you'd have to use the Boussinesq equations AND DOUBLE THE CALCULATED LOADS. At some point you may want to say close enough as you may end up with a building that's a few dozen feet away and the calcualted effect is just a few psf.
If you have cohesivs soil, discount cohesion (it'll fatigue over time). I'd expect a lower friction angle and greater stresses on the wall (or a further distance requirement).
f-d
¡papá gordo ain't no madre flaca!
RE: How Far Back to Hold Building
RE: How Far Back to Hold Building
Richard A. Cornelius, P.E.
WWW.amlinereast.com