sub foundation washout

[Eric Andre]

We have an old building at the mill and one u-drain had a hole and washed a lot of soil under the slab and also under the footing of few collumns. so we have a huge cavern and the access to bring material is difficult as it is at the center of the building.

the plan is to resolve the sewer issue and then replace the sub foundation under the footing...

the difficulty is the access to the location so some people suggested to pump lean concrete into the hole.

I was wondering if someone have suggestions on this or on a other approach

the hole is about 20x20x40 ft3, some footing are floating in the air some are partially supported...

 

[oldestguy]

Any chance of "drilling" a tunnel from outside with skid-steer, with usual bracing? Filling the cavity and tunnel later might be cheapest way. Sometimes moving more yardage with equipment is the best way.

 

[SlideRuleEra]

Consider Flowable Fill instead of lean concrete.

http://www.SlideRuleEra.net

http://www.VacuumTubeEra.net

 

[Eric Andre]

thanks Oldguy... I don't think it is feasible... the hole is about 150 ft from any edge of the building and there are tanks and chest foundations to go around...

 

[oldestguy]

OG once more. In a few cases similar to this I have had to do some compaction of what was placed, or raise up slabs or provide support for nearby footings. In these cases I have had the contractor leave pipes (sometimes just downspout "piping") ending in the "filled" zone, but sticking out for access. Then a grout was pumped in to raise the slab or to compact the loose soil left. A ready-mix truck and a concrete pump was all it took. An observer was necessary in case of too much lift. Of course higher pressure grout pump also could be used with stronger pipes for deeper compaction.

 

[ATSE]

I would make sure the local jurisdiction is made aware of the problem, and the building remains unoccupied. You might make a few enemies, but your building is not safe.
Make sure you can define the full extent of the problem, or your solution may be inadequate, and you may be on the hook for future problems.
You might need a 2-step solution. Fill immediately (for safety), then GPR or some other non-destructive testing to check for subsurface voids.

 

[cvg]

suggest cellular grout. It will expand slightly, filling all the voids and would be cheaper than flowable fill

http://tunnelingonline.com/cellular-concrete-filling-the-void/

 

[Okiryu]

Perhaps recommend also to re-route that sewer/drainage pipes from below the building to surround the building to avoid future problems. Since the building is old, I assume the underground piping infrastructure is old as well..

 

[Prepakt1]

In cases like this I suggest filling the hole with a large grout bag and pumping it full with grout to support the foundation. The grout bag will contain the mix and provide support. If you do not use a bag the mix will flow into all cavities and could plug drain pipes or just keep on flowing into connected cavities.

Intrusion Prepakt /marineconcrete.com