Shotcrete Retaining Wall with Tiebacks

[DeeVo]

I have the task of designing a series of retaining structures for a roadway stabilization. The "at-rest" lateral earth pressures are rather high(110 pcf max, as determined by a geotech). I am looking at both soldier pile walls with tiebacks, and shotcrete walls with tiebacks. The front face of the wall will be completely buried. This fact makes me lean towards shotcrete, because of lagging longevity concerns(The wall is permanent, with a planned life of 50+ years). The slope above the wall is horizontal, there is a 2' surcharge from the roadway above, and the water table is well below the limits of work. For scale, the walls range in height from 15'-30'.

Which solution would you suggest?

How do the two walls compare cost-wise?

Any additional comments or suggestions?

Thanks!

 

[PEinc]

With the high earth pressure (110 pcf/vf) you have, I assume this is an unstable slope (landslide condition). Correct? If so, you need to determine the tieback force and anchor length needed to give you the required factor of safety for slope stability. I'm not sure why your geotech is calling for at-rest pressures. At-rest pressures are not used in landslide control walls. They are usually not used in regular tiedback or cantilevered sheeting walls either because sheeting walls are usually flexible enough to develop active earth pressures.

I recommend you check out some of the many types of anchored walls being built by Schnabel Foundation Company.

Go to

http://www.schnabel.com

If you contact one of their local offices, you can get some good advice for your particular project.

 

[DeeVo]

Thanks for your response.

Yes, a landslide condition does exist. As a result of our original discussion with the geotech we decided to use the "at-rest" pressure. This was because we weren't sure which wall type we were going to use. I agree that the wall will move, and therefore the "active" pressure may be used. Unfortunately, the geotech already reduced his values, leaving the "active" pressure at 110 pcf, and reducing the "at-rest" from 165 pcf to 110 pcf. Are these numbers reasonable? They seem VERY high.
I have already determined the horziontal and vertical spacings of the tiebacks, along with the lock-off forces, the tieback diameters, and the bonded lengths.

What are the benifits of a shotcrete wall -vs- a soldier pile wall with lagging? Any idea on a cost difference?

 

[PEinc]

If it's a landslide condition, the wall should be designed to properly distribute the anchor load required to provide the necessary factor of safety for stabilizing the landslide. The required tieback force will most likely be much more than that calculated using active pressures. And, the pressure distribution on the back of the wall will not be triangular as it appears your geotech is suggesting with his 110 pcf (triangular?) load.

Again, I recommend you talk to someone in the landslide wall design/build business - such as Schnabel. Their web site has a number of project examples. Also, to stabilize the landslide, you may not actually need a traditional "wall". Anchors can be installed without soldier beams or lagging and still stabilize the slope.

Go to

http://www.schnabel.com/schnabel/landslide.shtml