Friction angle of crushed rock
Friction angle of crushed rock
(OP)
I am trying to determine the at rest active pressure when backfilled with clean crushed stone. I have used a frictin angle of 41 degrees but I need some imput as to this being proper. I know from experiece that this type of backfill produces less pressure on the wall than grandular sand-rock fill but I don't know how much. I posted this on the structural site some time back but got no response.





RE: Friction angle of crushed rock
RE: Friction angle of crushed rock
Hope this helps.
f-d
¡papá gordo ain’t no madre flaca!
RE: Friction angle of crushed rock
RE: Friction angle of crushed rock
RE: Friction angle of crushed rock
If you just dump it in, then 41 is far too high.
If it is compacted, then it maybe is OK.
Since you want to limit the pressure on the wall do this, if you can:
Dump it in in lifts and compact only that material more than 2 feet out. This leaves loose stuff against the wall and provides good resistance to movement for the bulk of the backfill. The loose zone acts as a cushion so that you can develope the active out in the compacted zone.
Don't worry about settlement of the loose zone, since it hangs up on the wall and the compacted zone, the silo effect. It does not develop pressure like a liquid as a result.
Never compact next to the wall unless it is designed for far more than active pressure. Many a wall has tilted in because of this effort.
RE: Friction angle of crushed rock
RE: Friction angle of crushed rock
RE: Friction angle of crushed rock
RE: Friction angle of crushed rock
on one building that the owner asked us to look in to why everything was cracking, we cored several holes in the floor slab. one core was located about 10 feet behind the cast in place wall. the core drop about 6 inches. since i couldn't really see down in there, i stuck my camera down in to the hole and took pictures all the way around. the subgrade under the slab right near the wall had settled at least a foot. the wall was backfilled with #57 stone that was dumped in with a trackhoe bucket and not densified. the entire area was in a cut so the underlying soils were not related to the problem as far as we can tell based on the boring data we had at the site. the wall itself had zero cracks on the face. it all looked to be due to the crushed stone backfill behind the wall settling out over about 3-5 years.
RE: Friction angle of crushed rock
RE: Friction angle of crushed rock
True enough, last year I saw an RC wall visibly cracked in one place, intact everywhere else. When I questioned the builder, he answered it was due to backfill compaction.
Not too good to crack the wall even before it starts doing its job!!
RE: Friction angle of crushed rock
and that does not mean that you can't still compact with small equipment in thinner lifts. i've seen contractors argue that since they couldn't use a large sheepsfoot roller right behind the wall, they couldn't compact behind the wall. that's foolish. get a small walk behind compactor and compact in 4-6" max lifts or use a mechanical hand tamp compacting in 4" lifts. if that is still too much stress on the wall, then go to home depot and buy the personal hand tamp and put it in in 2" layers. i doubt anyone would actually argue that a mechnical hand tamp will overstress a wall with 3000psi concrete that has cured out to 75% of the design strength. just keep the larger equipment at least 5-10 feet or more off the wall.
RE: Friction angle of crushed rock
f-d
¡papá gordo ain’t no madre flaca!
RE: Friction angle of crushed rock
I amamazed that the answers range from 30 to 45 degrees.
Nothing really definite to base a design on.
RE: Friction angle of crushed rock
RE: Friction angle of crushed rock
RE: Friction angle of crushed rock
Evaluation of Properties of Rockfill Materials
by N. Dean Marachi, Clarence K. Chan, and H. Bolton Seed,
Journal of Soil Mechanics and Foundation Division, ASCE, January 1972.
RE: Friction angle of crushed rock
I'll try to dig out the references and post later.