Assuming you don't care if there is some indentation due to compression of the pavement or its modulus of elasticity, you probably are planning to use a method that involves soil shearing. Thus, the strength characteristics of the pavement structure and the soil below can be estimated or determined from testing (field or lab). Such testing likely means some field evaluation and possible test in place. You may have some indication of that with your apparent borings, as related to blow count, or possible in-place shear tests. Density usually is found from field tests, usually involving large samples, but nuclear testing methods also may be applied. You may have to involve experienced consulting engineering firms for finding what you need.
Finally you need to apply some method of relating eccentric footing loads into your bearing capacity formula. It may involve some approximations however.
Another method may be considered. That is an actual bearing test, called plate bearing test, which then has to be extrapolated upward to the size of your foundation pad. That extrapolation is an estimate, not precise, due to the larger pad affecting more zones below.
If it were me, I'd start with that plate bearing test to get an idea of just what I am up against for the larger size pad. This extrapolation probably means your full size pad has less bearing capacity than the plate bearing test result.
