Anchor Reaction Block Design

[aeoliantexan]

We are designing permanent post-tensioned anchors into shale to stabilize a 3H:1V cut slope. The anchors will be inclined 30 degrees from horizontal. The reaction blocks will bear against soft clay shale, very stiff clay, or alluvial sand. I have tried analyzing the blocks using passive pressure against a battered retaining wall with a sloping backfill and also as footings, using bearing capacity formulas. I am not really comfortable with either model. How do others approach this?

 

[ishvaaag]

From your description it seems you have the blocks at the feet of the slope. If it was proven that the cut slope is stable long-term, you would have mainly to prove that the foundation outfit is enough to keep the things safe and reliable. But if this is a new cut, with no akin experience besides, not even the slope stability can be taken from granted. Hence a study of overall slope stability may be also required, because it might fail even down under the foundation of the stopping block foundation, even if competent enough to force the failure elsewhere than at its toe.

If you can think that for sure you will have a toe failure, it is still a case to be considered in the overall slope stability study. Furthermore, the formulas of bearing capacity usually are derived for symmetrical long-wall footings, and the bearing of these walls or blocs is unsymmetrical in that one side has far less overburden than the other.

In all this means that I see more prospective success for analysis in the slope stability hypoyhesis, assuming logarithmic spirals or the locus of maximum shear stresses revealed by 2D plane strain analysis for the soil.

 

[ishvaaag]

The fact of the loading slope being shale needs also be acknowledged with plane failures along the layers. In that case the passive resistance at the stopping block seems a reasonable assumption.

 

[PEinc]

aeoliantexan,
I designed anchor blocks for one of these landslide walls for a PENNDOT job. Call me.

http://www.PeirceEngineering.com