Help with an engineers note. Thickened edge Slab foundation

[g1teg]

"Engineered granular fill as required, to extend out beyond edge of foundation a distance equal to the thickness of the engineered fill beneath the foundation"

Because my site is on a slope, I dug it out, am building a retaining wall, and filling up to grade with gravel compacted in 4" lifts. I will have roughly 50" of gravel under the pad.

On the sides of the slab with the retaining wall, I have extended my gravel 5' to the sides. On the side of undisturbed ground at grade, I extended beyond my slab by 1'. I've just noticed this note.

Why would I need to go out so far in all directions????

 

[mm08822]

The angle of repose of a given material indicates the angle made with the horizontal that the mtl will stay in place. Above this angle and the mtl will tend to collase until it reaches the angle of repose. Below this angle and there should be no collapse.

Eng is spec'ing the fill footprint so it is backfilled to be stable over the long term. If rise = run, as in your case, then you have a 45 degree angle.

 

[g1teg]

The angle of repose of a given material indicates the angle made with the horizontal that the mtl will stay in place. Above this angle and the mtl will tend to collase until it reaches the angle of repose. Below this angle and there should be no collapse.

Eng is spec'ing the fill footprint so it is backfilled to be stable over the long term. If rise = run, as in your case, then you have a 45 degree angle.

I get that, but in my case, 2 of the sides are up against existing ground, so it will be stable anyhow correct? Which is why I only went 1' beyond the pad.

That would apply to a pile above grade, but in the picture you can see there is a wall of original undisturbed soil.

 

[ConCretin]

I get that, but in my case, 2 of the sides are up against existing ground, so it will be stable anyhow correct? Which is why I only went 1' beyond the pad.

That would apply to a pile above grade, but in the picture you can see there is a wall of original undisturbed soil.

I think the way you have done it is just fine. It doesn't seem like the engineers note anticipates a fill of varying depth. Run out distance should equal depth of adjacent fill rather than deepest fill.

 

[larry4406]

The angle of repose of a given material indicates the angle made with the horizontal that the mtl will stay in place. Above this angle and the mtl will tend to collase until it reaches the angle of repose. Below this angle and there should be no collapse.

Eng is spec'ing the fill footprint so it is backfilled to be stable over the long term. If rise = run, as in your case, then you have a 45 degree angle.

+1!

The footing applied pressure spreads at a 45 degree angle per text books so the engineer specified 1:1 fill material to ensure the load was distributed properly.

Can’t help you regarding the sides where you intercepted good material. Get your Geotech involved if necessary.

 

[kbs2244]

Talk to your inspector.
He is the one who has to signoff on the rough site.

 

[tarmy]

Ask your engineer to provide a cross section typical detail for the various conditions you have. They should have, on hand, those typical details...usually showing a 1:1 slope (or some version that is appropriate) to natural undisturbed native material.

 

[mm08822]

Ask your engineer to provide a cross section typical detail for the various conditions you have. They should have, on hand, those typical details...usually showing a 1:1 slope (or some version that is appropriate) to natural undisturbed native material.

I would do this. ^^^^. At least get a sealed letter referencing your dwg.

If that pile of eng'g fill is within the pad area, how does it get compacted in 4" lifts?


What are the details of the retaining wall?

 

[g1teg]

I would do this. ^^^^. At least get a sealed letter referencing your dwg.

If that pile of eng'g fill is within the pad area, how does it get compacted in 4" lifts?


What are the details of the retaining wall?

I've dug down about 50" from the high (grade) side. That was about 18" lower than the bottom of the retaining wall. I dug that deep to hit bedrock.

I've started filling it in with gravel by hand. Spreading it in 4" lifts. I am at the base of my retaining wall at this point, and will begin building the wall, while filling the entire hole with 3/4" clear.

Each truck does about a 4" layer, so I am able to compact between loads, where the truck dumped.

 

[g1teg]

Ask your engineer to provide a cross section typical detail for the various conditions you have. They should have, on hand, those typical details...usually showing a 1:1 slope (or some version that is appropriate) to natural undisturbed native material.

Yeah, the engineer said he can't rely on the existing soil, standard is for it to extend 1:1, and won't change it..

That just created a bunch more work!

 

[mm08822]

Yeah, the engineer said he can't rely on the existing soil, standard is for it to extend 1:1, and won't change it..

That just created a bunch more work!

If he performed a load bearing soil analysis to have possibly used less eng'd fill, you would have paid more for the engineering design. Crusher run stone is cheap.

Your problem is you are backfilling by hand. You will be spent before you start to build. You need to rent a small loader and get it done quickly w/o killing yourself so you can get to the fun part.

 

[tarmy]

Yeah, the engineer said he can't rely on the existing soil, standard is for it to extend 1:1, and won't change it..

That just created a bunch more work!

Sounds like your engineer does not have any site specific geotechnical info...and is relying on experience in the general area. I was an owner of a Civil engineering and surveying firm...and based on your info...that appears to be what he is going with. I am assuming there was no soils report specific for the project as well...

Well...in the case...as mentioned, your labor and rock is cheap! Better to be a bit on the cautious overbuild side...than have settlement issues later. Good luck OP...hope you are young!

 

[g1teg]

Thanks Guys

Yeah, I didnt pay for a soil test, cause I was on bedrock and he wanted a test every 24" after the initial. That would have been 4 tests total... too rich.

I paid for the Grading plan and the foundation plan.

Yeah, I did the last 4 trucks by hand, but I'll extend the hole and infill the rest with a Skidsteer. I'm young, but not that young (37 now). I just hate paying $1000 for a rental, when that is a nice table saw or something!!

I think Ill extend the hole on the low side, and move the retaining wall back 4' instead of digging into the walls.

 

[brownbagg]

so the water get away from the foundation

 

[mcbane]

Thanks Guys

Yeah, I didnt pay for a soil test, cause I was on bedrock...
.

How did you grade the bedrock? Drilling and blasting or did you get through it with an excavator and ripping tooth?




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[g1teg]

How did you grade the bedrock? Drilling and blasting or did you get through it with an excavator and ripping tooth?




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I needed 12" of compacted gravel beneath the retaining wall. I knew bedrock was close, so dug some test holes. It was at 18" so I dug to it the entire depth. 18" at the retaining wall, 50" at the yard side. I have not removed the bedrock

 

[johnnyradiant]

Thanks Guys

..... I just hate paying $1000 for a rental, when that is a nice table saw or something!!

The only problem with that line of thought, which is very common in my head and also my wife's, you don't have any time left to use the saw.

 

[g1teg]

Thanks All,

15 tri-axles later, I am at the bottom of the thickened edge slab (footing). I did rent a skidsteer, and its great. Only thing is, the loads seem to have gotten smaller since I rented that...