A column carrying a vertical downward load of 270 k is to be supported on a 3 ft deep square spread footing. The soil beneath this footing is an undrained clay with su = 3,000 lb/ft2 and unit weight of 117 lb/ft3. The groundwater table is 1 meter below the bottom of the footing.
a. Using the ASD method, compute the width B required to obtain a factor of safety of 3 against a bearing capacity failure.
b. How does the factor of safety change if the groundwater table increases to the depth of the bottom of the footing? Why?