CLSM Lateral Pressure on Tall Face Abutment 2

[OK_Engineer]

I am working on a tall faced abutment that will have CLSM (Controlled Low Strength Material) behind it. I am curious as to how much lateral pressure to design the abutment stem for?

In the past I have assumed it acted like soil and applied 120 pcf. Unfortunately this abutment is 30' tall and this is giving me a larger footing then I was anticipating. I would like to know if this is too conservative of an approach? Oklahoma DOT only allows for 4' lifts at a time so the CLSM would not act like a fluid once it has dried.

Thank you

 

[bridgebuster]

I did this for a bunch of walls. You calculate lateral pressure per lift, I.e. The first lift exerts a pressure, then it dries, no lateral pressure, place the next lift and it exerts a pressure, etc. the moment arms increase but you have the dried CLSM to balance things. I have to look back at some calculations tomorrow to see what Ka I used.

 

[BridgeEI]

I believe ODOT practice is to use 75psf for cured lifts and 90pcf for wet. No k factors included on top of that. I’ll double check in the morning.

 

[OK_Engineer]

Thank you both for your responses. Bridgebuster that would be great if you could tell me what Ka you used.

BridgeEI I would very much appreciate if you could double check that or provide where those numbers came from. Is there someone at ODOT I could get in contact with about this?

Thank you

 

[bridgebuster]

I looked at my calculations. I didn't use a K factor; used 100 psf for a wet pressure

 

[GC_Hopi]

You would need to consider two design conditions. The short term condition when the CLSM is fluid. It is conservative to assume it is fluid and exerts a hydrostatic pressure based on its unit weight. You can direct the contractor to limit the placement height and use some additional factor of safety. Then the other case is the long term condition. It would be good to check a standard soil pressure case, in case the CLSM is removed and replace at a future date, and also the case for cured CLSM. For cured CLSM, you may consider using the same Ka as your soil. CLSM is fairly weak in shear therefore it is logical to expect the CLSM to have the same failure surface as the soil that is exerting the lateral pressure on it and the soil has a more conservative angle of internal friction when compared to CLSM.

 

[BridgeEI]

Those are the correct values that I listed. This was also discussed at the thread below a while back.

thread607-424947

If you want to verify, contact the engineering manager within bridge division for your project. They should be able to verify or let you know if the practice has changed. Unfortunately it’s an unwritten rule since they don’t have any design policy written anywhere, you just have to know the right individuals to know their practice.

Also, if you have an expansion abutment be sure to check the lateral deflection at the top. That has caused issues in the past for other consultants.

 

[Ron]

This condition can be handled like lateral concrete pressure on formwork.


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