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design Anchor force on SLOPE W

design Anchor force on SLOPE W

(OP)
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.

RE: design Anchor force on SLOPE W

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.

RE: design Anchor force on SLOPE W

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.

www.PeirceEngineering.com

RE: design Anchor force on SLOPE W

1 m seem too near to slope. it is necessary consololidation before excavation. it is in seismic zone?

RE: design Anchor force on SLOPE W

(OP)
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.

 

RE: design Anchor force on SLOPE W

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.

www.PeirceEngineering.com

RE: design Anchor force on SLOPE W

To add to PEinc's thoughts, why not draw a 10 m excavation with surcharge loading at 1 m distance.  Add static earth pressure using Terzaghi/Peck trapezoid + any seismic and water earth pressure?  

Chapter 7 of this book covers your topic better than any other book I have read:

http://www.amazon.co.uk/Engineering-Design-Geotechnics-Fethi-Azizi/dp/095559961X/ref=sr_1_2?ie=UTF8&qid=1291948817&amp;sr=1-2

Alternatively, you can get SoilStructure.com Lateral Stress Software Program to do this analysis for you.
  

RE: design Anchor force on SLOPE W

(OP)
Thanks guys for your inputs.

I will try to get both CivilTech Software's Shoring Suite and
SoilStructure, to see how they work.

Thanks again

RE: design Anchor force on SLOPE W

You can download a demo version of CivilTech's programs.

www.PeirceEngineering.com

RE: design Anchor force on SLOPE W

Again, MOST shoring systems are flexible.  This may be an underpinning project that also requires lateral support with tieback anchors.

www.PeirceEngineering.com

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