Flowable Fill as Retaining Wall Backfill
Flowable Fill as Retaining Wall Backfill
(OP)
Just wanted your thoughts on using flowable fill as backfill behind a retaining wall (actually an exterior/end building wall) . If I'm trying to avoid any water behind the wall, does flowable fill help. How would I go about calculating lateral pressures as I think there will be a reduction in pressure with the use of flowable fill (due to self-bonding nature...like concrete) as compared to low-plasticity backfill (even with a clean stone zone). Based on the amount of water added to flowable fill, I would think it is very porous and may end up with hydrostatic pressures anyway, or am I wrong. Also due to expected high lateral pressures when its still plastic (just placed), will placement of say 4 ft thick lifts be ok without have to shore up the wall?
Your thoughts are welcomed
Your thoughts are welcomed





RE: Flowable Fill as Retaining Wall Backfill
Just some initial thoughts - and don't forget about your drainage!
f-d
¡papá gordo ain’t no madre flaca!
RE: Flowable Fill as Retaining Wall Backfill
Mike McCann
McCann Engineering
RE: Flowable Fill as Retaining Wall Backfill
Lateral pressure against the wall may be a function of the geometry of the flowable backfill (after it sets, of course). A narrow column of rigid backfill simply transmits the pressure developed by the soil behind it to the wall. A mass of rigid backfill wide enough to act like a gravity retaining wall by itself may exert very little lateral force against the wall after the wall moves a small amount. For an intermediate width, I would look at sliding wedges cut behind the backfill.
RE: Flowable Fill as Retaining Wall Backfill
RE: Flowable Fill as Retaining Wall Backfill
Is there some reason you can't backfill with regular pit run? If it's in a tight spot, you could always use wet sand; the city of Seattle uses it for their utility trenches due to it's ease of placement and lack of big stockpiles and heavy equipment. It's placed with a regular concrete mixer, and self-settles(not completely, but better than nothing). If you're running into water problems, you can just use 2-4" angular rock. Easier to compact, and would drain the side of your wall nicely.
RE: Flowable Fill as Retaining Wall Backfill
RE: Flowable Fill as Retaining Wall Backfill
If you are trying to reduce pressures against the wall, consider flyash stabilization of the soil to reduce pressures.
Flowable fill will likely transfer the transient forces to the wall unless poured at a 45 deg slope from the heel of the footing, which may be costly.
There are flowable fill designs that can set up very fast. Depending on the length of the wall, lifts can be 1ft or so. (Wear boots that protect your feet. These mixes are hot). If you have a perimeter drain, you will likely fill it up with flowable fill.
There are so many considerations when using flowable fill, that it may add quite a bit of cost. I recommend using stabilized fill, drainage fill behind the wall and perimeter drain if possible.