What measures to take under slabs where good compaction is unlikely 2

[IJR]

Friends

I have a slab on grade carrying storage loads. Somewhere this slab is interrupted by a wall that goes down into earth to form a part of a channel.

Now at the junction between the slab and the wall there is a 90 deg bend and a fill there is not likely to be well compacted being next to a wall which will be cast in place before the slab is cast.

What additional measures must be made down there

Thanks IJR

 

[Ginger]

If the area of slab adjacent to this downstand wall is to carry loads from your stored materials then I would probably consider filling behind the wall with dry-lean concrete or a similar material which will not subsequently compact. This solution assumes that your slab is neither structurally tied into or sitting on top of the wall.

If you have already backfilled with granular material but are convinced it does not have sufficient bearing capacity, then consider pumping grout into the interstices to stiffen up the backfill. Be careful with this one not to pump at too high a pressure for fear of blowing the wall over.

If your slab supported by the wall then I think you have to provide sufficient rebar in the slab to span the distance from the wall to the good subgrade. If this is too far then you may have to consider small piles with a reinforced slab. Another solution if the fill area is too large is to use vibrated stone columns as a ground improvement technique which will incrase the bearing capacity of the fill.

Regards Andy Machon

 

[IJR]

Thanks a million Ginger. In which time zones are you stationed?(You dont have to answer this of course)


IJR

 

[Ginger]

IJR

Operate in all time zones 24hrs a day!!!. My employer doesn't allow us poor engineers to sleep. Anyway, least I could do to after the sterling work you did on my connection problem.

Regards Andy Machon

 

[KAM_imported]

IJR please see my response posted under CISGeotechnical's recent question by accident. It is in the geotechnical engineering forum. Sorry for the mix-up.

 

[IJR]

For the rest of my friends equally interested, here is KAMs response as previously posted in Geotechnical forum

*THANKS KAM*


I am assuming the fill and slab are already in place. If you are not sure of the fill compaction, why not have a geotechnical consultant drill thru the slab in a few places and perform manual auger borings with penetrometer testing every 6 to 12 inches? While this would not tell you the exact unit weight of the fill, it would give you a relative idea of the soil stiffness. You could have a few additional borings done in areas of the slab where you know the fill was properly compacted to calibrate the penetrometer data to the suspect area.

If the soil was not compacted properly and is sandy, it can be chemically grouted to give it a cohesion component and turn it into a weak sandstone. Another option might be to remove the slab in this area, preload the soil with stacked product, and then re-pour the slab with adequate jointing. A specialty ground modification contractor, such as Hayward-Baker, could install compaction grout columns from the base of the slab to a firm soil layer to transfer slab loads through the weak zone. Grouting tends to be expensive.

 

[ishvaaag]

I being more familiar with structures than with geotechnical studies would compact the best possible, and if doubt remains would bridge as above indicated. If bridge approach slabs receiving 16 tonners at 100 mph can live with a 6.5 m long slab, great must be the problem to not be economical the bridging.