Cantilever retaining wall - sliding and bearing check

[Teesa]

Hello,

I am examining an existing retaining wall for sliding, overturning, and bearing checks.

For dimensions, see attached.

I have checked overturning, and it is okay, but sliding is not. The cantilever retaining wall has a shear key. According to the Canadian foundation manual, passive resistance above the frost depth should not be considered.

I need help calculating the sliding; it is failing in sliding:

Factor of Safety (FSsliding) = ∑Resisting Force/Driving force

The resisting force is Vertical force x Tan θsoil + Hp Hp = 1/2 γH2Kp = 1/2 x 22 x (500/1000)2 x 3.3 = 10 kN (a very small force).

For the driving force, I used lateral earth pressure and lateral surcharge pressure.

I want to know, when we have a shear key, how do we calculate the resistance provided by the shear key?

Second question: when calculating the bearing pressure, the eccentricity is greater than B/6, which means that the eccentricity of the load is less than one-sixth of the base width of the retaining wall.

How do I calculate the soil pressure? In one of the old posts (

https://www.eng-tips.com/viewthread.cfm?qid=461662)

I found "I get e > L/6 condition, Hence, I applied the 2P/BL' to calculate pressure max; where L' is the bearing length = 3* (0.5L-e)

Thus, Qu = 2P/BL' = 102.6 kNm2"

Can someone please let me know what the formula is to calculate soil pressure when e > b/6?

Thanks,

 

[DoubleStud]

Wouldn't it just be a triangle with center of gravity at the eccentricity? The area of the triangle will be equal to the resisting force? The triangle will stop before the end of the heel.

 

[raligt]

I have some old university notes which answers your queries. See attached

Your passive pressure acting on your shear key and base would help with sliding. Combined with dead weight of wall + shear key.