retaining wall with clay backfill

[broekie]

Does anyone out there have experience with designing reatining walls with clay backfill. I have a situation where I need to evaluate an existing wall. I have never designed one with clay backfill (only sand). The material that I have gives 2 methods. The vertical reinforcing in the wall seems low, so for now I am only looking at the bending momnet at the base of the wall. Later I'll get to global stability. Both methods assume that a tensile crack forms at a depth equal to z=2c/gamma/Ka^0.5.

Method 1 - Neglect the tension zone and calculate the moment at the base of the wall based on a soil pressure that is 0 at the depth z calculated above and is at the pressure at the base of the wall calculated using normal methods. Add this to the moment at the base of the wall due to the tension crack filling with water.

Method 2: Draw an alternative pressure diagram that starts at 0 at the surface and extends to the same pressure at the base of the wall as calculated in Method 1. This method ignores any water in the tension crack of the soil.

Is one of these methods more conservative than the other or 'accepted" practice? Thank you.

 

[frv]

I've used method 1.

However, the pressure was given to me by a geotech as an equivalent fluid pressure. This pressure will depend on whether you have an active or an at-rest condition (essentially, whether you allow the wall to rotate slightly or not, respectively). If you can find an equivalent fluid pressure in the literature, then simply distribute it as a triangular load. Be aware that you may have a surcharge pressure if there is load on top of the soil behind the retaining wall.

It's been my experience that global stability is usually the controlling parameter.