Question

QUESTION 3 A 3-ft wall footing is subjected to a contact pressure of 5000 lb/ft 3. The wet unit weight of the cohesive soil supporting the footing is estimated to be 100 lb/ft 3 and groundwater is estimated to be 20 feet beneath the footing. The minimum depth of the test boring is ft. Submit answer to the nearest foot,

Answer 1

Given,

3-ft wall footing

Contact Pressure = 5000 $lb/ft^{3}$

Wet unit weight = 100 $lb/ft^{3}$

Ground water at 20 ft beneath the footing

Contact Pressure = $\gamma * 20+(\gamma - \gamma_{w})*(D-20)$

5000 = 100 * 20 + (100 - 62.4) * (D - 20)

3000 = 37.6 * (D - 20)

D - 20 = 79.79

D = 99.79 ~ 100 ft

Minimum depth of test boring = 100 ft