Underpinning vs Epoxy Resin Injections

[rainybroons]

I negotiated the half-duplex for $8000 less than first agreed, based on quotes from tradespeople after getting a structural engineer because of the slight sinking. If anyone has any experience, knowledge, or can offer the contact info of someone who knows about which method I should use over the other, that would be much appreciated.

The soil is a mud/clay soil that has expanded and contracted and the yard has many very large cracks. I believe this is what has caused the few mil sinking on one end of the house but I'm not sure which method to use. The duplex is 30 years old and didn't have soil testing in the day. I have provided pictures before if you do a search of my posts if you'd like to see visuals.

Thanks for any advice you can give - I'm very confused which way to go. Price isn't the big worry as there's only a couple thousand difference - it's which will last given the house will continue to expand and contract with these soils.

Any advice about fixing the yard would be great too

 

[wylie]

For our son's house, we got quotes from two underpinners and one epoxy resin injection company. The latter company was selling its method as cheaper, but it wasn't cheaper at all, once we got into the nuts and bolts of it.

Once I realised an old work make is an underpinner, he came out and told us without any BS just what needed doing. He wasn't interested in talking us into spending money with him (it was fortunate to have it straight from an expert who wasn't trying to get our business).

We ended up with hubby doing extensive drainage totally around the house, removing a backward sloping patio to stop rain running against the house walls and ensuring rain ran away from the house where it had been running towards the house for 50 years.

If we ever get any rain we will know for sure it has worked.

I would get in a couple of underpinning companies to quote. Try to dig around to see if it really needs underpinning or maybe a few "spot" pins will be enough?

 

[willair]

I negotiated the half-duplex for $8000 less than first agreed, based on quotes from tradespeople after getting a structural engineer because of the slight sinking. If anyone has any experience, knowledge, or can offer the contact info of someone who knows about which method I should use over the other, that would be much appreciated.

The soil is a mud/clay soil that has expanded and contracted and the yard has many very large cracks. I believe this is what has caused the few mil sinking on one end of the house but I'm not sure which method to use.

Look into 20mm drainage gravel around the area where the slab has sunk
sometimes that can fix the problem by taking the water away more quickly,
but look at this in serious terms,a 30 year old slab will give a bit over time

,i had one property a 2011 flood job that the centre pillar sunk 110mm.when we had a big storm a few weeks ago,all the doors in the central area jamed,ect,had too go in under the building and jack it all up again slowly over 2 days then reset new larger pillars black soil is always a problem area when it rains..good luck..

 

[Zeddy]

In my experience, underpinning/injections are generally good only when dealing with subsidence due to bearing failure of the foundation.

When used to attempt to remedy distress from reactive soil movements, often the signs of distress will recur as the underpinning does little to halt the reactive soil movements. If any, the signs of distress will be transferred to different/adjacent locations on the structure.

In addition, there is always the risk with injections that there might be a leakage path eg wide crack. This can cause a blowout of injection costs, as there is usually a variable component to the quote based on the volume of material used.

Personally I would not be looking at the path of underpinning. Instead, if you must, I would recommend the installation of control joints and spending some of that $8k in carrying out cosmetic maintenance.

Disclaimer: I do not know the specifics of your case, and the above covers broad, general terms only. In diagnosing the problem, geotechnical tests should be carried out to determine site reactivity, soil allowable bearing capacity, etc before coming to a conclusion. If your engineer has carried out these tests/has significant local knowledge that may replace them, then it may override the above.

 

[rainybroons]

Here's the structural report.

Thanks - I've just realised the Uretek picked up that the front bedroom window also has cracks - and the engineer didn't, so I've asked him to re-attend and modify his report, but that makes the underpinning quote higher.

I've contacted a couple of geotechnical engineers to get quotes and possible further proposals, and will look into control joints as I know nothing about them.

Thanks for making me think about what needs to be done to fix this, but also stop future cracking appearing.