Bearing Pressure of Cantilever Retaining Wall

[Brian0723]

Example: I have a cantilever retaining wall in soil (like in the attached photo), and I am looking to check the soil bearing pressure. I know the net ultimate bearing capacity of the soil and I also know that by the definition of net bearing pressure, only the additional weight is considered (that the weight of the soil above has already been included). In the bearing pressure calculations you need to find the sum of the moments at the base as well as the sum of the axial loads, which then in turn gives you your eccentricity which is used to find the total bearing pressure at the base.

My questions is this: when does the weight of the soil (and wall) get considered in the calculations? It would make the most sense to me that the eccentricity is calculated considering all loads (soil above the toe and heel of the retaining wall as well as the self weight of the wall itself), but then the bearing pressure at the base is calculated using this eccentricity, but the axial load used in the bearing pressure calculation would be only the portion of the wall above grade (on either side), along with any soil weight that is above the grade on the other side of the wall. This makes the most sense to me as the soil and wall weight need to be considered for the appropriate eccentricity calculation, but as I am checking against the net bearing pressure, the soil above should not be considered. Please let me know any thoughts or questions you may have.

 

[DaveAtkins]

I would just calculate bearing pressure using all loads, and compare it to total allowable bearing pressure (net allowable plus soil overburden weight).

DaveAtkins

 

[BridgeSmith]

To add to what DaveAtkins posted, the soil overburden would be for the depth in front of the wall. For the retaining walls I've designed, I've found it to be small enough to neglect, considering the typically substantial variability in the soil properties, including the bearing capacity itself.

 

[Guest090822]

You use all the loads. Sometimes the passive soil resistance is ignored if there is eveo a chance of future excavations.
AASHTO has effective footing width and lengths taken into consideration to account for eccentricity.
This is a fundamental problem, any basic foundation engineering book will have good guidance.