Gravity wall on slope with flat area 1

[haynewp]

I have the attached where the retaining walls have a proposed flat area on an otherwise sloped hill. I don't have any information on the soil properties at the site this will be going on. They are trying to adapt a standard DOT design based on assumed soil properties (friction angle = 28 degrees) to this case but the standard gravity wall would be limited to only 4'-6" high due to the slope according to the DOT drawing.

Can the level area behind the wall be used to decrease the force on the wall from the sloped backfill above this level area?

 

[Doctormo]

A trial wedge analysis can provide the thrust from an irregular backslope condition which should be less than the simple infinite slope condition. Solving for your model requires a math exercise with a spreadsheet. You could also approximate a lessor backslope (say 3:1) that would split the difference between the level and sloping sections as a rough guess.

However, building walls on steep slopes (2:1) can be quite risky. The concept of having a 26.6 deg slope with a 28 deg backfill material would not provide much stability prior to constructing a wall on the slope. A global stability analysis of the proposed construction would be extremely poor. You would really have to have some more positive information about the soils in the hill before guesstimating a design on a steep slope.

The concept of the horizontal bench is correct and having significant embedment on a slope is good, the exact amount can be argued about given the wall is not that tall. The 4' bench is typically an AASHTO requirement and would be a conservative position considering no soils information provided.