Today I began work on a home built in 1909 with a concrete porch that had fallen in. The floor was elevated six above a “crawl space” that had no access. It was poured over corrugated roofing supported by steel I-beams. The roofing and I-beams rusted out….
The problem now is filling the hole to pour new concrete. The people who sign my check say “Granular fill to within four inches.” However, the wall/railing is an original stone wall that will have 40″ above grade pressed with fill from the inside. About 140 tons of fill for the wraparound 8′ wide porch. Not to mention the concrete.
Shouldn’t there be something done to brace the wall from being pushed out? I suggested steel rods with plates connecting the stone wall to the poured foundation. “Too hard to drill through the stone.” I suggested raising the grade outside. “Then you won’t see as much of the stone wall.”
Am I worried for nothing?
Replies
yes, you are right to be concerned... flowable fill is just that .. it is flowable and exerts a high hydraulic pressure...
you have almost 4' of unbalanced moment... if the stone wall could be backfilled temporarily so the pressure would be equal on both sides until the concrete takes a set.....bracing and shoring will probably not do it.. it will only take one weak point in the stonework to blow out
other than that.. have a backhoe standing by to dig a hole for all the fill to run into when the stone wall breeches
Mike Smith Rhode Island : Design / Build / Repair / Restore
Locally the fill would be 1" limestone gravel...which is not flowable. This would mean that with an stone retaining 40" wall tall there would be about 6 cf of stone pushing against the wall, thus about 300# per linear foot of porch. Assuming an angle of repose of 45 degrees.
I would suggest a temporary set of vertical and horizontal bracings back to deadmen. These would lock into the porch floor perimeter forms which could be tied back into the house with rebar and connectors to diminish the top of the wall horizontal push.
Just a consideration.................Iron Helix
fooled me... the title "fluid rock" made me think of "flowable fill" which is juiced concrete....Mike Smith Rhode Island : Design / Build / Repair / Restore
I thought the same.....that's a lot of hydraulic push horizontally.
The 1" aggregate has no fluid hydraulics, but does have an angle of repose that generates some lateral force. I assume the new porch floor would be reinforced concrete of thickness to span from the stone porch front to the house foundation so that any settling of fill after the pour would not repeat the collapse.
Likewise if this structure is in a termite prone area, have the fill thoroughly saturated with termite dope by a licensed applicator.
Another option would be to cut in an access to the area under the porch. Install temporary forms and supports, pour a structural porch floor, remove forms, treat for termites, install access door.
.....................Iron Helix
What about a concrete "plank"? In this case, it would need to be made-to-measure, but it seems a tad more elegant (in the engineering sense) to span the space--which was the pre-existing condition as I understand it.
Andy Clifford has some recent experience with rock wall vs the weight of fluid materials. He might have some tips for you.
Joe H