This should help you:
“The supporting soil is called the “Cone of Compression” and radiates out at a 45 degree angle from the bottom edges of the foundation. If they interrupt the cone of compression they have compromised the ability of the soil to carry the weight of the structure above and the area compromised will need to be stabilized. The cure should be spec’d by a structural engineer.”
From dug out crawl space. - InterNACHI Inspection Forum http://www.nachi.org/forum/f23/dug-out-crawl-space-16892/#post201317#ixzz3BYeqHXS7