pelelo (Geotechnical)
6 Dec 10 16:32
Hello,
I am analysing an excavation using SLOPE-W.
About 1 m off the top of the 10 m excavation there is a 4 story building.
According to the results i get from Slope W, I need to use any kind of earth retaining system (FS<1) on the excavation in order to make is stable (e.g anchors, nails, etc).
My question is, how could i obtain the design anchor force from SLOPE W? Is there any way to do so? Or will I need to enter several anchor force values until I get the Factor of safety i am looking for?
Please let me know.

althi (Geotechnical)
6 Dec 10 17:26
There must be a way in Slope/W. I use Slide and it has an option 'show support forces' to get this data.
On another note, if you use grout anchors in the upper strata, there is a potential that the adjacent building could move up by inches.

PEinc (Geotechnical)
6 Dec 10 18:44
Be careful using a flexible sheeting system to support a 4 story building. I would not do that. It would probably be more appropriate to use conventional concrete underpinning piers, a secant pile wall, jet grouting, or a slurry wall (in increasing order of cost). Soil nailing is not appropriate for supporting a building, big or small. Soil nail walls require significant open cuts along and below the existing building in order to install the nails and shotcrete. A building can fall down before you drill the first nail or spray the first load of shotcrete. A soil nail wall needs movement to transfer load to the passive nail tendons. Movement means settlement of the building. Building settlement can mean injury, damage, and a lawsuit. A combination of tiedback or braced sheeting with micropiles to support the existing foundations may also be economical.



pelelo (Geotechnical)
7 Dec 10 20:12
Thanks for you reply.

We are planning to deal with anchors as due to the site restrictions a small anchor drilling machine will be more accesible than any slurry wall drill rig, or secant piles drill rig.

I don't see very clearly the required anchor force from SLOPE W. I see the free body diagram force from each slice, but no information is given regarding any additional force required to stabilize the slope. Or maybe slope W doesn't show any information at all.
What I think is there should be an easier way instead of assigning an anchor forces and trying to chase the FS you are looking for. Mayeb it would be easier if I try another software, any ideas?
The adjacent building is 1 m off the slope, consolidation is not necessary as the soil profile is silty sand (SM), with n values between 10 and 20.



PEinc (Geotechnical)
7 Dec 10 23:28
For the few slope stability programs I have seen, you enter in a tieback force, by trial and error, and then see if the safety factor is OK. The programs do not calculate the required tieback force. For a program that calculates the tieback force, you need a wall design program such as CivilTech Software's Shoring Suite. However, the wall programs will not do a global slope stability analysis, as far as I have seen.