I have a question about a forensic project i am working on.
This 1 story home is showing some cracks on the walls and the floor was surveyed and settlements of 2 inches in one of the corners were recorded.
The borings were drilled to a depth of 10 ft. Soils (sp) show n values between 4 and 12, ranging from very loose to medium dense sands.
Due to this problem, i got the loads from the structural engineer and he told me they are around 1500 psf.
I decided to run few settlement analyses calcs. Using 1500 psf, The settlement results yielded very low settlement values, nothing compared to 2 inches. Computed values were around 0.1 to 0.2 inches at the most (i played with E values provided by Das and Bowles, using worst case escenarios). For n <10, i used e = 10600 kpa, for n between 11 and 15, i used e = 15000 kpa.
After this i proceeded to compute the bearing capacity using the traditional equations (terzgui, meyerhoff, vesic). The results yielded ultimate bearing capacity values of around 2700 psf, on average.
From this, the computed FS (2700 / 1500)= 1.8.
Per the geotechnical references, A FS > 3 is recommended for bearing capacity purposes.
Do you think the reason of these settlements could be because of such low FS computed)?. I did not see soils around the footing heaving or bulging.
Df = 1 ft, B = 1 ft
Fyi, this project is in florida where lots of sinkholes occur. Somehow client only approved 10 ft of drilling.
Does my calcs make sense?. Please advise.