Backfilling with Stone

[Sean_14]

I have a situation where there is a CMU retaining wall that out the outside has about 6ft of soil higher than the inside. The wall has approximately a 40" deep footing (from the inside)only 2'x1'. On the inside 2ft worth of soil must be excavated due to contamination. The contractor wants to put back DGA instead of soil. Is there any benefit to this? My concern is that the DGA will not offer enough lateral strength to keep the wall from sliding.

 

[strucbells]

WTF is DGA?

 

[dauwerda]

Dense graded aggregate - also often called crusher run I believe.

 

[SwinnyGG]

In my area DGA is basically ABC that goes up to around 1 1/2" instead of 3/4" size.

 

[jayrod12]

If the stone backfill is compacted, it has always been my understanding that it is superior in strength to clay/soil backfill. That's for both gravity and lateral strengths.

 

[MotorCity]

I'd be interested to see how the lateral pressure of aggregate compares to that of soil backfill. Also would want to look at what sort of pressure that compaction imposes on the wall.

 

[jayrod12]

I believe the active lateral pressure is lower, however the passive resistance is higher. If I'm understanding the OP correctly, this backfill is on the low side of the wall, therefore should provide better resistance than clay/soil.

 

[Ron]

The phi angle of graded aggregate will be higher than most soils unless they are clean, coarse sands. So if on the passive side, that's good. On the active side...not so much.

 

[Settingsun]

Ron, are you saying not as much benefit on the active side as on the passive, or saying the higher phi is detrimental on the active side?

 

[Ron]

@steveh....my reply was a bit misleading. My point is that the passive increase is a little greater than the active decrease with increasing phi. For high loads, it could become a significant factor. (Rankine case)

 

[Sean_14]

Yes the back filling with DGA would be on the low side of the wall.