Subsidence on anew build

[Mullins]

Hello,

First time poster, I've been reading a good bit for the last while as I consider my build of the great resource that is the forum.

I have a question I would like to ask the collective brain. I recently moved house and in the past week I have removed 50ish evergreen/leylandia trees from my yard/garden. The trees were 25-30 foot tall and had not been pruned/trimmed in 10 years. Roots were pretty extensive and they were planted very closely together 20 years ago.

Removing the trees and roots was a big job and we took a digger. To get under and undermine and remove the roots in places we dug down 3-4 foot.

In summary the ground and area where I want to build my 36 oven (and hopefully parrilla style grill would not be "settled". I do not want to lay foundation and start a build if it will subside under the weight or move. How long should I wait?

Thanks,

Mullins

[gorazdr]

Re: Subsidence on anew build

I belive soil will take more than five years to compact naturally. You should use vibrating plate or vibrating hammer and compact soil layer by layer (about 6" at a time).

Gorazd

[UtahBeehiver]

Re: Subsidence on anew build

You need to excavate to undisturbed soil then compact in lifts, certain native materials do not mechanically compact well so might need bring some engineered material.

[Mullins]

Re: Subsidence on anew build

Thanks for the responses. I should have mentioned (completely forgot) that the digger was 3,5 tons and that would have rolled over the area a couple of times. Not systematically to compact it, but in levelling the yard it would have been rolled over a few times and compacted somewhat. Probably not as loose as I initially thought, but I guess I will have an indication as I begin to excavate...

Thanks for your help.

[Mullins]

Re: Subsidence on anew build

You need to excavate to undisturbed soil then compact in lifts, certain native materials do not mechanically compact well so might need bring some engineered material.

Excuse the ignorance, but what do you mean "in lifts"?

Thanks

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[UtahBeehiver]

Re: Subsidence on anew build

Maybe an American term, lifts are layers of material to be compacted.

[Mullins]

Re: Subsidence on anew build

Maybe an American term, lifts are layers of material to be compacted.

Gotcha.

A previous response of mine appears to have gone missing where I have clarified that the 3.5 ton caterpillar would have compacted the soil somewhat as the yard was levelled (the tracks may not have covered all the ground as the tracks did not pass over all of the ground systematically....)

[UtahBeehiver]

Re: Subsidence on anew build

Mullins,

The Cat does a decent job what we call in my trade (pipeline construction) wheel rolled or track rolled but on if done in lifts, if the Cat tracked over the 3-4 foot hole from the tree roots with no lifts the bottom part of the excavation most likely not compacted (if this is where you want to put the oven). That's why compaction is done in lifts.

[Mullins]

Re: Subsidence on anew build

Mullins,

The Cat does a decent job what we call in my trade (pipeline construction) wheel rolled or track rolled but on if done in lifts, if the Cat tracked over the 3-4 foot hole from the tree roots with no lifts the bottom part of the excavation most likely not compacted (if this is where you want to put the oven). That's why compaction is done in lifts.

I was afraid someone was going to say that! Thanks for your advice...

[Gulf]

Re: Subsidence on anew build

I was afraid someone was going to say that! Thanks for your advice...

I'll have to be another one to second that. I would mark off the site for the oven and begin digging. Mind you that the top crust under the dozier tracks will seem solid. I have had to use a pickaxe to get down 8", only to find nothing but loose fill underneath. If you get down a foot in one corner to good solid subsoil, quit digging in that corner. Go to the opposite corner. Dig until you find the solid subsoil, even if that is 4 feet deep. Do the same in the other two corners. Now taper all four quadrants of your dig to together to form a solid but most likely an uneven bottom. Now fill the entire dig with crushed gravel or a similar fill up to the level that you want to start your concrete slabs for the oven and parrilla .

[NCMan]

Re: Subsidence on anew build

This thread quickly reminded me of an outdoor fireplace (not a WFO, just a stand alone fireplace) that was apparently built on fill/unstable ground. I wish I had taken a photo. It had sunken on one side about 6-8 inches. Anyway, long story short, they had to tear it all down and ended up taking the mason to court. I was asked to bid on the job and politely declined, since I actually knew the mason that built it originally. I wasn't getting involved w/that mess. No way. Not sure whatever happened after that. I strongly agree w/what you are being told. Get down to solid ground and be below frost level and you are good to go.

[Mullins]

Re: Subsidence on anew build

This thread quickly reminded me of an outdoor fireplace (not a WFO, just a stand alone fireplace) that was apparently built on fill/unstable ground. I wish I had taken a photo. It had sunken on one side about 6-8 inches. Anyway, long story short, they had to tear it all down and ended up taking the mason to court. I was asked to bid on the job and politely declined, since I actually knew the mason that built it originally. I wasn't getting involved w/that mess. No way. Not sure whatever happened after that. I strongly agree w/what you are being told. Get down to solid ground and be below frost level and you are good to go.

I have read a number of posts about frost, frost heave and the frost line. I am Irish where we do not get ridiculously cold weather due to the Gulf Stream, living in continental, landlocked Luxembourg where it can drop to below 20 Celsius or below 5-10 Fahrenheit (according to online conversion tools) for 1-3 weeks a year. How do I know how deep the frost line is here...? Where in the US might have comparable cold weather climate I could ask forummers who live in similar climates...?

(Edit to say) A quick google is suggesting Maryland, Connecticut, Oregon, Oklahoma, Delaware, Tennessee and Virginia would have similar winter averages.

Thanks

Mullins

[NCMan]

Re: Subsidence on anew build

I would think your local permitting office would be able to tell you. I have lived in Maryland before (born there), I can only tell you that where I lived and worked there, the frost line was 30". To me, it's tough to imagine all those states having the same frost line. It's possible, I guess. I would still try your local permitting office. They should know or be able to guide you to where to find out.

[Mullins]

Re: Subsidence on anew build

I would think your local permitting office would be able to tell you. I have lived in Maryland before (born there), I can only tell you that where I lived and worked there, the frost line was 30". To me, it's tough to imagine all those states having the same frost line. It's possible, I guess. I would still try your local permitting office. They should know or be able to guide you to where to find out.

I based it on average temperatures as per here. Average Winter Monthly Temperatures by USA State - Current Results

Give or take a couple of degrees. I realise that is only average and the lowest temperatures would be significantly lower...

Will ask an architect (girlfriend of a friend of mine...

[NCMan]

Re: Subsidence on anew build

I based it on average temperatures as per here. Average Winter Monthly Temperatures by USA State - Current Results

Give or take a couple of degrees. I realise that is only average and the lowest temperatures would be significantly lower...

Will ask an architect (girlfriend of a friend of mine...

Also,something to keep in mind....when a frost line is referred to, it means that the bottom of your footing or slab must be at or lower than that elevation. And keep in mind where your final grade will be, since it's at that level you should be measuring from, not necessarily from the existing grade. In other words, figure out where your final grade will be and determine your frost line from there.