Effect of Expansive Soils on CMU Retaining Wall Design 1

[Sierra Dave]

I've got an plan check note in Sonora, California for a 75' long x 7' tall CMU retaining wall that I must provide expansion joint detailing per TMS 402-16 Sec 4.1.5 because the Soils reports cites expansive soils in the area. CalTrans CMU retaining wall details call a joint every 90'. I thought expansion joints mainly take care of thermal and curing changes? Is it possible the plan checker is just mentally connecting on the words expansion and expansive?

 

[emmgjld]

Possibly not confusing the terms.
If you have expansive clays beneath the footing, the footing is to be designed to account for the expansive clays AND
the cut slope and/or part of the backfill may also exert additional pressure on the wall.

 

[Sierra Dave]

Thanks emmgld. It still seems to me that expansion joints take care of longitudinal shrinkage and expansion and that the Geo's EFP takes care of soil conditions. Expansion joints are usually designed not to allow out of plane deflection. I would not think that expansive soils would be pushing or pulling on the ends of a wall.

 

[dik]

90' is way too long a space for an expansion joint in these environs...

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[Sierra Dave]

Thanks Dik. I don't object to adding expansion joints. I just can't figure out how I would prescribe them based on a calculation involving expansive soils.

 

[haynewp]

I think it's getting confused. Any wall joints aren't going to be much help in mitigating the expansive soil. I would verify the EFP actually does include this from the geotech and some other mitigation isn't required for expansion behind the wall or beneath the ftg.

 

[Sierra Dave]

Thanks haynewp. Can anyone connect me with a quantitative method of prescribing expansion joint spacing?

 

[OldDawgNewTricks]

NCMA TEK 10-03 Control Joints for Concrete Masonry Walls - Alternative Engineered Method.

 

[dik]

Not sure... it's a matter of designing the wall to accommodate possible expansive soils, by piling if necessary. It the soils can move, it's also a matter of accommodating the movement, likely by sufficient control or expansion joints. JAE had a neat comment in another thread making the distinction between the types of joints.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[haynewp]

Piling would be introducing a different system that could mitigate heave. I had assumed this is shallow foundations on expansive soil. I've never seen wall expansion joints used to accomodate expansive soil. It would seem they would have to be frequently placed relative to the 7ft wall height, continue down through the footing, and also without a shear transfer method at the joints in order to be effective.