Soil slope to consider in retaining wall

[spieng89]

See below sketch. I have a situation where directly behind the retaining wall I have one slope then it starts to gradually increase beyond the vertical plane of the heel. My question is what slope should I consider? And if I would like to consider the shallower slope how far beyond the vertical plane of the heel must the grade be made shallower? I have been combing through my soil books and resorces online, but haven't come up with a definitive answer. Any input is appreciated

 

[BAretired]

Does the slope start to increase or is it negligible beyond the plane of the heel? Note on section contradicts your text.

BA

 

[spieng89]

BA that's my markup showing what I would like to consider negligible. I looking to find a reference beyond engineering judgment to prove so

 

[BAretired]

Strange wording. You seem to be suggesting that the slope beyond that artificial boundary need not be considered. If so, I don't believe you are correct, but would prefer to hear from a geotechnical engineer.

BA

 

[oldestguy]

Here are some copies from US Navy`Design manual for Soil Mechanics, etc. old version. going on line it is there but maybe different Figure nos.

 

[BridgeSmith]

The slope above the footing only matters in calculating the resisting weight of that block of soil and in calculating the height of the lateral forces on the wall. The lateral loading magnitude, direction, and height of application all are functions of the slope from the back edge of the footing to where the zone of influence ends.

Put another way, the soil above the footing is the resisting mass and everything behind the footing is the retained soil.

 

[spieng89]

Hmm I may need to figure steeper slopes. Problem is those slopes are technically above the soil friction angle which means the soil is unstable, but in reality it's been fine for more than a decade.

Would not the extent of the failure plane of the soil play a part in where the slope needs to be considered. See below. My thinking is that extending the failure plane to the back-fill surface would create the max distance where I would need to consider the slope. Anything beyond the failure line should be negligible. This would be a better scenario then having to consider soil 25ft behind my 8ft tall retaining wall.

 

[BridgeSmith]

Yes, the slope within the failure wedge is what you would have to consider as the backslope for design.

If you have a backslope that's already close to failing, how are you going to excavate to get the wall in place?