Retaining wall with shear key sliding (LRFD)

[precast78]

Guys,

If I am understanding correctly the friction coefficient in front of the shear key is soil to soil (approximately TAN phi), and the friction behind the shear key is concrete to soil (approx 2/3 * TAN phi). My question is, how do you split up the vertical forces? How much contributes to concrete to concrete and how much to soil to concrete? I want to hear all of your opinions.

 

[msquared48]

I only consider the frictional force of the base against the soil, not the soil in front of the toe. I figure that is conservative, giving me a little latitude for the FS for sliding.

Mike McCann, PE, SE (WA)

 

[precast78]

Yes Mike, that is what I do too. But you will have 2 different friction coefficients if you use a shear key.

 

[msquared48]

I see what you are saying... finally.

Well take the force from the soil pressure prism in front of the key and apply the soil to soil C there, and use the soil to concrete for the force from the pressure prism at the heel and apply the soil to concrete C.

I normally just take the total force and apply the soil to concrete C. If a shear key is needed, then I try to have that take the majority of the shear force. The force generated by the key will transmit to the soil/soil interface in the rotational failure plane, so the majority of the lateral resistance is in the toe of the wall.

Heck... avoid all the hassle and just put in a slab!

Mike McCann, PE, SE (WA)