Question

Read sections 3.1 through 3.5 pp. 133-143 and solve the following problems: 1. For the following cases, determine the allowable gross vertical load-bearing capacity of the foundation. Use Terzaghi's equation and assume general shear failure in soil. Use FS = 4. Part B 4ft 2m 3m D 3ft 1m 2m ' 25° 30° 30° c' 600 lb/ft? 0 0 Foundation Type Continuous Continuous Square 110.0 lb/ft 17.0 kN/m' 16.5 kN/m b. Redo problem 3.1(a) assuming that a local failure occurs in the soil. Redo problem 3.1(b) assuming the simplified bearing capacity model for frictional materials that was developed in the class is valid (class notes, volume 4, p.20-22). Comment about the possible reasons for the differences you get between the answers of problem 3.1 above (general and local shear) and your current simplified analysis.

Answer 1

Answer 1) a) For continuous footing of B = 4' and Df = 3'

Nc = 25.1, Nq = 12.7 and Ny = 9.7

Thus qnult = cNc + YDf (Nq-1) + 0.5YBNy = 600*25.1 +(11.7*110*3)+(0.5*110*4*9.7) = 21055 psf

qns = 21055/4 = 5263.75 psf thus Gross bearing capacity = qns + YDf = 5263.75 +(110*3) = 5593.75 psf

b) Nc = 37.2 , Nq = 22.5 and Ny = 19.7

Thus qnult = 17*1*21.5+ 0.5*17*2*19.7 = 700.4 KN/m2

Thus gross bearing capacity = 700.4/4 + (17) = 192.1 KN/m2

c) qnult = 16.5*2*21.5 + 0.4*16.5*3*19.7 = 1099.56 KN/m2

Thus gross bearing capacity = 1099.56/4 + 16.5*2 = 307.89 KN/m2