Retaining Wall Question - Infinite Backslope Vs Broken Backslope

[ahardy89]

At what distance from the face of the wall is it ok to assume the backslope "infinite" and disregard where the backslope is broken (and any surcharge associated with broken slope)?

For perspective, lets say you have a 8-foot tall retaining wall with a backslope at 3H:1V which is broken 10-feet from the heel of the footing. Where the slope is broken, there is a parking lot. Is it ok to assume a infinite backslope condition and assume the vehicle surcharge is far enough away (distance of surcharge > height of wall) from the wall that its affect on the lateral pressures is insignificant? Or should you calculate the earth pressures with the backslope and conservatively add the vehicle surcharge lateral pressure as well.

 

[r13]

I think it is depends on the method you have used to design the retaining wall. You should determine the active/failure wedge accordingly.

 

[BAretired]

For an eight foot high retaining wall, looks like assuming an infinite slope is going to be conservative. The weight of cars will be more than offset by the weight of assumed soil.

BA

 

[ahardy89]

BAretired - That is what I figured. So if I am using Coulomb theory with the backslope factored into the active pressure coefficient, at this distance the surcharge from the parking lot would not need to applied on top of the active pressure.

Is the rule of thumb if the surcharge is a distance equal to the wall height (or a 1:1 plane) from the heel of the footing, the surcharge effects on the wall are negligble?

 

[r13]

Influence zone of surcharges.

 

[BAretired]

Is the rule of thumb if the surcharge is a distance equal to the wall height (or a 1:1 plane) from the heel of the footing, the surcharge effects on the wall are negligible?

For me, this situation did not arise often enough to have a rule of thumb. With railroad tracks or highway loading nearby, it might be wise to consider the load and soil properties more carefully. But in your case, parked cars produce less load than dead weight of soil, assuming an infinite 3H:1V slope.

BA