A building is to be constructed in an area where the ground surface is horizontal. The groundwater table at the site is very deep. For a point within the soil mass, 10 feet below the surface, the...

A building is to be constructed in an area where the ground surface is horizontal. The groundwater table at the site is very deep. For a point within the soil mass, 10 feet below the surface, the preconstruction vertical effective stress is 1,120 psf and the horizontal effective stress is 560 psf (consider these stresses to be principal stresses). After construction, the vertical stress at the same point will increase by 440 psf because of foundation loading and building use. Assume the horizontal stress will be unchanged.

(a) Indicate the change to the maximum shear stress at the described point that will occur because of the construction.

(b) Assume that after the building is completed and occupied, the groundwater table at the site raises to within 6 ft of the ground surface as a result of area rainfall. The vertical effective stress in the soil mass changes because of the high water table. Determine the maximum shear stress (effective stress conditions) at the analyzed point in the soil mass for the changed situation if the horizontal effective stress is unchanged (from part a) by the rising water table.