Filling Footing Trench With Washed Stone
Filling Footing Trench With Washed Stone
(OP)
In our area, crappy soil is common so digging down 5 to 6 ft for a strip or spread footing happens alot.
Most geotechs I encounter just tell the builder to fill the hole with washed stone and then pour the concrete on top of that.
How does that actually work? Wouldn't the excavation walls have to have sufficient strength be able to keep the gravel "column" from spreading out? How do they know that?
Thanks
Most geotechs I encounter just tell the builder to fill the hole with washed stone and then pour the concrete on top of that.
How does that actually work? Wouldn't the excavation walls have to have sufficient strength be able to keep the gravel "column" from spreading out? How do they know that?
Thanks





RE: Filling Footing Trench With Washed Stone
RE: Filling Footing Trench With Washed Stone
We had a contractor before who tried to backfill beneath footings using a GAP 7/20mm aggregate. It only had particles between 7-20mm in dia. It wasnt compacting to 98% MDD which wasnt a surprise. We made him remove it an replace it with a well graded angular aggregate.
RE: Filling Footing Trench With Washed Stone
RE: Filling Footing Trench With Washed Stone
I will assume you are referring to more of the coastal plains soils than the Piedmont soils in your area. If so, they are not greatly different than those that we deal with here in Florida.
Using washed stone as backfill for any significant depth in a trench is not a great idea, particularly because of the raveling that OldestGuy notes. We generally limit its use to creating a mud mat where the trench bottom is saturated and you don't want to place concrete in standing water. This usually limits its thickness to about 6 inches and it is intermingled with the poorly graded fine sands to stabilize them and to allow concrete placement in the dry.
RE: Filling Footing Trench With Washed Stone
I am actually dealing with the piedmont plastic clays mostly - not the coastal soils
RE: Filling Footing Trench With Washed Stone
As for the "minutia".....it is necessary for structural engineers to know basic soil properties and earth pressures (in particular). The more we know about other disciplines with which we interface, the better our understanding of the design and construction as a system. After all, a structure is a combination of discrete elements (soil, concrete, structural steel, rebar, wood, etc.) working together as a system.