D. Solve the following problem. A structural engineer has hired you to design square concrete unembedded footings for a building, based only on capacity. Each footing will hold an axial

load of 180 kN. Your technicians have conducted lab tests on specimens sampled from the site, and they report the following profile: a 2-meter thick sand layer over a 7-meter thick gravel layer (the gravel layer lies over rock). The lab report reveals that the friction angle of the sand is 33 degrees, and that of the gravel is 39 degrees. Determine the size of one of the footings, in meters, such that the short term factor of safety against a capacity failure is between 3 and 3.3. Show all your work, organized, and circle your answer.