How many feet away from a 2 floor house foundation does soil have weight (stone, concrete)

[IDontKnowWhyIDidIt]

Just out of curiosity. I have a 2 floor house. The foundation footings are probably 18 inch width. I know the weight of the foundation on the soil immediately below is the largest and then it reduces as per the width of the footing. Here is some information I found which states that the weight reduces by the width size depth wise. I am not sure how do I know breadth wise how long does the weight extend. How many feet (in breadth and not depth) outside of the footing should the soil not be disturbed because its carrying the wight of the foundation. I think its simple math but I can figure it out. Any experts here?

BTW, this is out of curiosity and I am not doing any DIY

Thanks

[JonahWicky]

The load path extends out at a 45 degree angle below the footing.

[Ted Bear]

What do you mean by disturbed? I would NOT straight down along the footing and expect that the whole thing won't crumble into the trench.


45 degrees does sound reasonable. An engineer would know exactly.

[lunetunelover]

45 degrees is a safe bet to start, but it depends on the type of soil, it's angle of repose (if I remember my geotech classes), it's optimum water content, and some other factors. Your safest bet is to see if you can get a geotechnical engineer to do some quick testing and give you a better idea.

[K'ledgeBldr]

The value of the spread (angle path) is determined by the soil type and moisture content.

Over the years I have had to have soil compaction tests done- part of that test would be to "cook" the soil sample, removing the moisture and then re-weighing the same, detrimining the moisture content.

To arbitrarily assume that 45degrees is the starting point could be detrimental to the foundation. But, since this is merely an exercise of an equation...

[chet everett]

Technically there should be NO support provided to the home by any of the soil that has been backfilled around the foundation. The purpose of backfilling is ONLY to allow for an smooth transition for landscaping and such. In fact, improper backfilling, such as dumping material that has too much stone / concrete chunks or backfilling before the foundation is properly cured, can severely damage the home...