Hi everyone, I’m considering the purchase of land for the purpose of constructing a residence and shop. The current owner of the land is a builder who had a customer back out of a contract. Prior to the customer’s cancellation, the builder dug the footings for the foundation. If I purchase the land, I would have a completely different design for the structures, and possibly in a different location within the 2 acres. Let’s say worst case, some portion of the footings for my plan coincide (i.e., overlay, intersect, etc.) the old footings. Is it practical/reasonable/safe to fill and compact the old footings, then dig the new footings? I am grateful for any insight. Thank you, Rick
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Replies
It all depends.
On the soil, on the structure, and on the location.
Short of inventing a time machine, the best you can do with soil that's already been excavated is to compact it. If I were in your situation, and my floor plan called for footings that intersected, or had near misses, I'd excavate down a bit further than the depth of the current footings, that way you can ensure the entire footing plane is compacted uniformly, assuming the soil is the same over the area of the floor plan.
Small lifts of washed angular gravel in appropriate widths (determined by the soil's bearing capacity) when compacted into (most) soils will provide ample support for residential structures. If you really want to be sure, have an engineer look it over. Otherwise, a pocket penetrometer will give you some indication about the bearing capacity of the soil at the surface.
In the case that the footings cross at angles where the back fill may shear off and generally be a pita, I'd just leave it excavated in that area, and back fill when you're done with the other parts.
Is this a monolithic slab/footing? If so that may change my opinion.
Thank you! Actually two slabs, one for about a 2000 sq ft residence, and another for about a 5000 sq ft shop. You can see the footings in the attached pic. Thanks again for your thoughts! Rick
Rick,
It's hard to tell the composition of the soil from the picture, but it looks like it has some clay content, since the footing walls appear to be intact. Do you have any reports on it, or can you perform the jar test? https://hgic.clemson.edu/factsheet/soil-texture-analysis-the-jar-test/ . Once you have that information you can loosely correlate the bearing capacity under saturated and dry conditions. It's better just to measure it directly though.
How deep/wide are those that are currently dug? I think I'd still plan on simply digging my footings to a depth that was below those, should they intersect, and be sure to compact the fill afterwards. I think that's about all we can say until you had a floor plan for the two buildings in relation to that site.