Me...My hole...and the mystically selfcompactable #57 Stone

[Farmer1402]

We have begun excavation on my house where I've taken on the pleasure of being the GC. I had a large Sweetgum tree removed which was in line with the front of the house. After laying out the footings, the hole where the tree was is exactly where the corner of my foots for the grarage wall. My excavator says we can clean up the soil (to an undesturbed level) and fill to grade with #57 stone and pour the footings across that (hole is 6' wide and 3' deep). Code says undisturbed soil or engineerd fill. Is #57 Stone an "engineered fill".

 

[Ron]

#57 stone is not "engineered fill". That is usually soil of similar character or improved over the surrounding or native soil. "Engineered" means that some consideration has been given to its soil classification and compaction to achieve a structurally sound bearing soil.

#57 stone has a large void volume, which can be filled with surrounding soil raveling into those voids by groundwater movement and by surface water infiltration.

Use select structural fill material and compact it in accordance with acceptable compaction standards.

 

[Farmer1402]

Thank Ron. The county inspector suggested I backfill 6" at a time and tamp. The footings sub wants me to get an geo engineer and the excavation sub wants to fill with #57 stone. I may just shift the house back 5' and deal with more fill around the whole house.... Since none of my local resource thus far have given me a definative answer Whom do I go to get the select structural fill material and where can I reference the acceptable compaction standards? Thanks Again.

 

[bridgebuster]

Farmer,

Your state DOT will have specs for select structural fill along with compaction requirements. Most, if not all, DOT's post their specs on line.

 

[cvg]

what does the building department say? The inspector will want to approve this, you may want to confirm with them. you did get a permit didn't you?

 

[Ron]

I'm assuming from your post that you are in the US, but we don't know where. If my assumption is correct then, the International Building Code or one of its state variants is likely controlling the process.

Engineered fill would be soil material that is free of deleterious materials, construction debris, organic material, or any rock material greater than 1" in size. The material should contain no more than 10% fines (clay, silt or a combination) and should be classified as GW, SP, SP-SM or SP-SC.

The material should be placed in lifts not to exceed 8" in thickness and compacted to achieve an in-place density of not less than 95% of the modified Proctor maximum dry density. This is similar to what your County Inspector told you...he's right.

Fill material is usually available in most any area...call around. You might be able to get enough for this application from your own site by re-grading or from your footing excavation in other areas.

 

[Farmer1402]

Thanks Again Ron and everyone. I have a permit and I've tried to talk with them twice but get non comital answers. Basically I figure it out and they will let me know if I got it right. I contract to the US Dept. of Energy, this is a typically gov't answer. Can't blame them though. If i get direction from them and it turns out wrong, who's liable? The project is in SC.

I've got plenty of soil from the excavation. The house has a full basement with walkout. Soil, I am told, is excellent 1/8" and less gravel with not much sand. We have been able to drive a 50,000lbs excavator on it with the soil fully saturated (which is my other problem we are working but that is easier to solve) with no visible trace of disturbance from the tracks. So soil is possible SP.

 

[Ron]

Farmer...you go it right. They will tell you when you are wrong, but not much else...as it should be.

Your soil could be a GP or SP...in either case, sounds fairly good. From your soil description and the fact that you have a basement, I assume you are in the piedmont area of SC, not the coastal plains. Typically good foundation material when compacted.

 

[Farmer1402]

Yes and no. A little more direction as to the solution would have been helpful, but they are not there to engineer.

I think my solution is a s follows: I'm moving the house back 5'. Filling the bottom of the hole with gravel and a perforated pipe connected to the french drain and compacting local seleced soil in 8" lifts to stablize the sides. In the footings along side the hole I'm going to have them put #4 rebar lateral across the footings. Should be best all around...exect for my budget!

 

[Ron]

Farmer....be sure to place a filter fabric (geotextile) around the #57 stone (top, bottom and sides) to prevent the surrounding soils from raveling into the voids. It will create a depression above if you do not do so.

 

[dgillette]

Farmer's post gets the 2012 prize for "Most Amusing Title in a Technical Forum," even though 2012 isn't over yet. That's going to be hard to top.

 

[Ron]

dg...agree!

 

[Farmer1402]

Well, spoke with my excavation sub and he assures me he can compact it. He said he will much the hole, fill the bottom and sides with gravel and compact 8" lifts with selected site soil. He said he was bringing compaction equipment for the french drain anyway so it would not be a problem. No more #57 stone... except for my construction entrance. I originally hired him to bore under the road for a force main line to my remote septic field. His regular business line is utility and DOT Contracting so he's got plenty of equipment and people and been in business for 30 years.