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Do not know if I’m under engineered.

4 feet in depth, individual 3000lb block to form walls (seating area), on geogrid between 6” of 1 1/2 angular stone, and on top of blackland prairie soil.. I have a dry well to hide the rain over flow.

https://gardening.stackexchange.com/questions/57669/geotechnical-engineering-classification-and-percolation

Top Yellow Seating back - recessed off 6” off; Bottom yellow block - 3000lb seating; Between Stone and base? Geogrid; Dark grey - Base; Light grey - Gravel sides Brown around sides it just undisturbed dirt.

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This is a close up of the subdivisions back filled garbage soil, never mind the irrigation we’re cutting it out next week, but we don’t want it to flood like the rain did and paused us during construction.

NathanPtexas
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    What are you trying to support here? Is the mottled grey the concrete? What are the two different colors of yellow representing? There's a big gap in one wall, is that a door? How big is it? What is your actual question?? – FreeMan May 14 '21 at 12:10
  • Grey (sides) is gravel? For rain run off, the dark grey is some kind of compacted base maybe limestone or whatever compacts well below ground in NE Texas, then I want to place geogrid on that for an extra 10 year droop protection, the yellow are like this boulders cut @ 2’x2’x4’ which will be the seating they are heavy, and the brown at the bottom are just augered holes back filled with gravel for drainage hide away. – NathanPtexas May 14 '21 at 14:31
  • 3000 lb seating? Is that per foot? Under engineered? I would say over engineered, what is the compaction of the backfill? How deep? If that is concrete bits and soil I see no issues, if it was a true trash dump and that is styrofoam you have a big problem. – Ed Beal May 14 '21 at 15:26
  • @ed - doubt it’s per foot the entire thing is heavy and we want be different that’s why we like these quarry blocks, the augered holes will be 4-5’ deep down center, I guess just any rock compacted will help hide water settlement until it percolates deeper, then 6” of some good rock to keep it in place so in reality it’s above the water, but if it sits in water will the base shift? Geo on top of that then the heavy block and the gravel behind is kind of built like a retaining wall for run off and slowing potential flood water. – NathanPtexas May 14 '21 at 15:34
  • I see a question _mark_ up there, but no real question. Please take the [tour] and revise to be more specific. – isherwood May 14 '21 at 15:35
  • What is the reason to have 3000 block notation I understand 3000psi concrete or 5000 for example what is the number pertaining to? Just one note below grade concrete tends to wick moisture (I could not use in my area) the stone work may always be damp, – Ed Beal May 14 '21 at 17:19
  • @ed - have you ever seen “butter blocks” at parks and such areas? They are for seating, this is a sitting area around a firepit 3-4’ below ground flush with the jacuzzi. – NathanPtexas May 15 '21 at 03:14
  • Nathan, I have not but I live in Oregon, if it’s not raining it will be soon so concrete/ stone seating may not be as common as other parts of the country. – Ed Beal May 15 '21 at 22:31
  • @ed - def, thanks for the advice, the idea for my drainage and 6” rise is to basically hide run off until it percolates, I’ve seen the “sunken pits” or “in ground firepit” areas or such, the ideas are forming from them. – NathanPtexas May 16 '21 at 20:30

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You didn't mention what is the foundation to support, a patio with deck is very different from a 2-stories building in concern of settlement tolerance.

The settlement is a function of soil bearing strength and footing area, for a concentrically loaded foundation, the bearing pressure is the total force (superimposed dead load + live load + footing self-weight) divided by the footing area, the resulting bearing pressure must not exceed the allowable bearing strength. For the dry condition, you can obtain the presumptive bearing pressure from the building code, or from the local building department provided that you know the type of the underlying soil. However, if there is the presence of groundwater near or above the bottom of the footing, you shall consult a geotechnical engineer for guidance.

r13
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  • Well we don’t need a permit for our diy, it will be below ground on raw soil built up on stone base, but on the link to the landscaping exachange the photos are attached, with more information, it might help give a visual.0 – NathanPtexas May 14 '21 at 01:27
  • The photos do not help to identify the soil strength, which either provided by the code or by testing. Otherwise, it is in your own hand, nobody can help. I wouldn't worry if it is for a small deck. The soil and the depth seem adequate for that purpose if the footing is placed over gravel on the dry ground. – r13 May 14 '21 at 01:45
  • No deck, heavy blocks will go on top of the base, is the base enough, specific kind or addition geogrid? – NathanPtexas May 14 '21 at 02:58
  • What is the purpose of the block if it is not supporting anything? – r13 May 14 '21 at 03:14
  • To sit on it with guests it will be a in ground firepit area. I uploaded a 3D model of the insides cut out to see the structure of it.. drains, base, geo, block, just want it to stay put and not sink, flood (in the future) or shift. – NathanPtexas May 14 '21 at 03:40
  • Then I don't see why you need 4' depth. You shall set the stone on a slightly raised ground that allows water to flow away freely. For stability of the stone, a few inches of sandy gravel fill below it will do. – r13 May 14 '21 at 03:46
  • Sandy gravel instead of the rock base? Well the idea is to flush it level with our jacuzzi later on we will place pavers or sod, some lighting around the yard and it will be nice. – NathanPtexas May 14 '21 at 04:51
  • Yes, compact the sandy gravel well. In the cold region, a layer of rock/gravel fill can be placed below the sandy gravel to cut off the path for capilary raise which will lead to the freeze and thaw (heave) problem. – r13 May 14 '21 at 05:07
  • @r13 instead of clarifying the question in comments on your answer, it would be much better to clarify it on the question itself. That way, it's much more obvious for others who may come along later. – FreeMan May 14 '21 at 13:03
  • @R13 thanks bro, I will consider the 6” of sandy gravel on top of the subsoil; should I place the geo grid (already purchased) on the subsoil or sandy gravel; by sandy gravel do you mean the kind that’s is crushed different sizes and compacts well (they say) – NathanPtexas May 14 '21 at 14:26
  • Yes, you can place the geogrid on the subsoil, and yes, I meant a well-mixed backfill that consists of different sizes of gravel. – r13 May 14 '21 at 16:43
  • You are welcome. Good luck with your project. – r13 May 15 '21 at 12:23
  • @r13 - one last thing, drainage;should I do something like a dry well, or a few deep post holes? – NathanPtexas May 16 '21 at 21:18
  • I think a sump pit will do. – r13 May 16 '21 at 21:27