Sloped Site
Sloped Site
(OP)
Hi
I've been asked to look at some retaining works for a sloped site and have some general queries. See attached sketch.
How do you calculate the sloped fill element on retaining wall B as a surcharge load?
The site soil is a firm clay, is it correct to position wall B just outside the 45 degree zone of influence (for load spread) from wall B or should I push it further away from wall A? I'm concerned that the formation dig for wall A will run into the zone of influence (for load spread) of wall B.
When designing wall A I assume wall B will have no effect if it is located outside the 45 degree zone of influence (for load spread)?
Any advice welcome.
I've been asked to look at some retaining works for a sloped site and have some general queries. See attached sketch.
How do you calculate the sloped fill element on retaining wall B as a surcharge load?
The site soil is a firm clay, is it correct to position wall B just outside the 45 degree zone of influence (for load spread) from wall B or should I push it further away from wall A? I'm concerned that the formation dig for wall A will run into the zone of influence (for load spread) of wall B.
When designing wall A I assume wall B will have no effect if it is located outside the 45 degree zone of influence (for load spread)?
Any advice welcome.






RE: Sloped Site
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RE: Sloped Site
RE: Sloped Site
1. Excavation shown is not deep enough to construct Wall A of the "Proposed Dwelling".
2. The footing for Wall B is on fill. IMHO, not good.
3. The soil (fill?) is described as clay, not granular.
If the excavation is made deep enough to construct Wall A, the footing for Wall B is placed deeper (on undisturbed soil), and only granular backfill is used, then construction and lateral pressure problems become more manageable.
The above recommendations are not "cheap"... but should result in a design that actually works.
www.SlideRuleEra.net
www.VacuumTubeEra.net
RE: Sloped Site
I tend to agree with cvg that the slope on the right of Wall B is probably too steep. A slope stability study is definitely needed.
BA
RE: Sloped Site
Mike McCann, PE, SE (WA)
RE: Sloped Site
RE: Sloped Site
Wall A: why wouldn't the wall be designed to be integral with the house - in other words the house wall would also be Wall A.
For computing the pressures, which hasn't really been discussed, there are computations for sloping fill above the wall - or one could use the Coulomb graphical method.
In looking at this, I might suggest to the right of Wall B to have a berm of a couple of metres. For the angle of the slope in the shaded area to the right of the top of B, one could use a fabric MSE slope which has been used many places in the past - and use granular fill in the stabilized section. This would act as a buttress to the clay slope above.
As pointed out by others, a global stability check should be carried out.
RE: Sloped Site
RE: Sloped Site
I think your idea of soil nailing is good, see attached sketch. What tell tales should I look out for on site for potential slippage of the lower slope segment (pink zone)?
J
RE: Sloped Site
RE: Sloped Site
While your last sketch may be what you end up with, at this stage all such options should wait until an experienced geotech engineer has completed a detailed investigation and has doe the initial stages of a global stability analysis. As you move along, more such stability checks may be needed for the option you want to do. If you do have a drainage capable fill behind a wall, be sure the geotech OK's the gradations used. Too many commonly used drain systems plug up because proper filtering was not in the job. A lot of void space may look good, but it also fills with mud.