Cantilever Retaining Wall Sliding 8

[SteveGregory]

I normally design a retaining wall footing for a Sliding SF = 1.5. I use a friction factor for the dead loads and a passive pressure against the toe to reach the SF required. Any soil or dead load above the footing toe can be used as a surcharge to the passive pressure.

In the past, I have used the same passive pressure to add to the resisting moment. Also, I used the same passive pressure when calculating the soil bearing pressures.

For equilibrium, the sum of the horizontal forces has to be zero. So, the passive pressure may be zero or very low depending on how much frictional resistance is available. Passive pressure won't be present until the active pressure sliding force exceeds the frictional resistance.

This will change my bearing pressures in a more conservative direction. Am I thinking correctly?

 

[STrctPono]

I thought about another case where I utilize keys in retaining wall footings and it is almost impossible to avoid.... When designing a bridge concrete end post that is the transition piece from the bridge to the metal thrie beam connector off the bridge. These foundations are generally shallow and you typically don't have a lot of soil weight on the heel of the footing so it can be extremely difficult to rely solely on friction. Inclusion of a concrete key can help to resist the sliding of the footing due to a vehicular impact load. It's pretty much unavoidable in these cases.

 

[r13]

This is where the safety factor kicked in - the active earth pressure is "demand", the passive earth pressure and the shear friction are "capacity", capacity meet demand in equilibrium, but with the capability to go beyond, if demand increases by the magnitude of the safety factor (Capacity = SF*Demand; Capacity/SF = Demand allowed).