Reinforce masonry wall to deal with settlement risk

[njtk1987]

TLDR: I think we messed up a foundation, anything I can do with masonry walls to mitigate settlement concerns?

In the last week, foundations were poured for my own single storey dwelling, 350mm thick, 1m wide, foundation design being 35N concrete reinforced with A393 mesh on the bottom.

Despite the excavator driver and building certifier being 'relatively' happy with the founding stratum, I just can't shake an unease with the founding soil under a gable end of the house which I feel was appreciably softer than the remaining house. I should have been more assertive before pouring, but we are where we are.

So I'm looking for anything I can do to reinforce the structure as it is built. The wall make up will be generally concrete cavity blocks with 100m leaves, supported by a rising wall of a concrete filled cavity or 100% blocks.

As a mitigation against settlement, I've been looking at mortar bed reinforcement, which is rarely (if ever) used for dwellings of this type where I come from.

Can anyone suggest other mitigations I could apply, or recommend an installation regime for the bed reinforcement?

 

[jhnblgr]

Well in the US typically footings are only 20”x10” deep so you are quite a bit larger than what I am use to. I would never use blocks but I think it’s more popular in Europe. You could additionally reinforce with bond beams to better distribute the load but block typically cracks at the slightest moment from my experience

 

[phamENG]

A lot would depend on the layout of the building and the construction type, as well as the limits of the soft soil. Is that masonry just a foundation stem wall with light frame above, or is it full height masonry? Given the size of the footing for a single story house, I'm guessing it's full height masonry.

Not sure about the economics of your area, but around here taking a couple borings to see the difference in soil strength between the gable end wall in question and the other end of the building would be cheaper than doing some structural gymnastics "just in case". If you find the soil is bad, then fix the soils rather than the structure.

 

[njtk1987]

A lot would depend on the layout of the building and the construction type, as well as the limits of the soft soil. Is that masonry just a foundation stem wall with light frame above, or is it full height masonry? Given the size of the footing for a single story house, I'm guessing it's full height masonry.

Not sure about the economics of your area, but around here taking a couple borings to see the difference in soil strength between the gable end wall in question and the other end of the building would be cheaper than doing some structural gymnastics "just in case". If you find the soil is bad, then fix the soils rather than the structure.

Yes, it’s full height masonry and a long 225sq m bungalow, where two pitched roof blocks are split by a flat roof section. A quick back of envelope calc indicates a bearing pressure of around 45-55kpa beneath the highest point of the gable end.

When you say ‘fixing the soil’… by what method? Underpinning?

 

[njtk1987]

Well in the US typically footings are only 20”x10” deep so you are quite a bit larger than what I am use to. I would never use blocks but I think it’s more popular in Europe. You could additionally reinforce with bond beams to better distribute the load but block typically cracks at the slightest moment from my experience

Yes, cavity block/brick is pretty standard in UK and Ireland

 

[phamENG]

by what method? Underpinning?

Underpinning, excavating the soft stuff and replacing with compacted fill, etc. If you still have options for changing the wall reinforcing, I'm guessing the wall isn't built, meaning the existing footing could be removed to excavate and fill if needed.