## CLSM Passive Pressure for Integral Abutments

## CLSM Passive Pressure for Integral Abutments

(OP)

Oklahoma has been using CLSM (flowable fill) as a backfill behind integral abutments for a while now. I just ran some numbers and am getting a passive pressure of 5 times that of granular backfill. I'm using a cohesion value of half of the compressive strength. I assumed a compressive strength of 150 psi.

Has anyone else ever looked into this?

Has anyone else ever looked into this?

## RE: CLSM Passive Pressure for Integral Abutments

By the way, if you enter the full name, rather than an abbreviation, it saves people looking it up.

Doug Jenkins

Interactive Design Services

http://newtonexcelbach.wordpress.com/

## RE: CLSM Passive Pressure for Integral Abutments

## RE: CLSM Passive Pressure for Integral Abutments

5x is interesting. I have a very unusual retaining wall project under construction where I'm using CLSM for backfill because I need to minimize active pressure. I'm not relying on any passive pressure but it's good to know it's very high.

## RE: CLSM Passive Pressure for Integral Abutments

Bridge EI, 90 pcf for a wet condition sounds about right. Do you mean 75 pcf for the in place unit weight/density?

FHWA says the friction angle is around 20 to 30 degrees with a cohesion value of 30% of the unconfined compressive strength.

https://www.fhwa.dot.gov/publications/research/inf...

"Once set, the fill has very high passive pressure resistance since it is essentially a concrete product. For this reason, it should not be used behind integral abutments where abutment movement could generate large passive pressures against the fill."Go figure.https://www.fhwa.dot.gov/bridge/prefab/if09010/03a...

NCHRP Report 597 reported measured friction angles of 30 to 40 degrees and cohesion values of 835 psf to 7200 psf depending on the mix design.

Either way it seems like a poor choice to put behind an integral abutment. Granular backfill makes more sense to me.

## RE: CLSM Passive Pressure for Integral Abutments

The CLSM around here isn't very well cemented. You can run your finger along it and leave marks well after it's cured. I have a hard time imagining it creates high pressures since it crumbles so easily so to me it would resemble a more compacted granular backfill. Other parts of the country may have something that's more dense/solid and warrants higher pressures.

## RE: CLSM Passive Pressure for Integral Abutments

I only have an expansion length of 114.5', so it's borderline if there's enough movement to develop the passive pressure.

## RE: CLSM Passive Pressure for Integral Abutments

## RE: CLSM Passive Pressure for Integral Abutments

I'm fairly certain that 75 psf is the active pressure against the wall. If the integral abutment starts moving into the CLSM, the passive pressures generated would be much higher than 75 psf or 0.5 psi.