Question

The main advantage of the hollow-stem CFA Is that A. it provides a very efficient method of drilling in rock formations. B. in situ resistivity methods can easily be used in conjunction with the hollow-stem CFA C C. disturbed, undisturbed, or core sampling can be obtained. C D. soil shear strength can be estimated from the rotational resistance of the auger during driing (C E. none of the above 41 A 10 ft high retaining wall retains level granular backfill Cef- O, Peff27, Y -115.0 pcf, ysat 122.4 pcf). During an intense and prolonged rainstorm, the water level behind the wall to rises to within 2 ft of the top of the wall due to an improperly designed drainage system and poorly graded landscaping. The total lateral force acting on the wall for the at rest earth pressure condition due to the rise in water level behind the wall is most nearly A. 1,996 lb/ft B. 1,005 Ib/ft C. 4,175 lb/ft D. 2,179 Ib/ft E. none of the above C

Answer 1

Main advantage of follow stem CFA is It provides efficient method of drilling rock formations option A answer H = 10 ft pi = 27 degree y_water = 62.4 pcf Y_sat = 122.4 pcf y_t = 115 pcf Kot 1 - sin pi Ka = -sin theta pi k_o = 1 - sin 27 degree = 0.546 At 2 ft just above force = k_o y_t H = 0.546 times 115 times 2 = 125.58 Just below Force - ko 1/water H = 0.546 times 62.4 times 2 = 68.14 At 8 ftl Force = ko [1/4 H + wat H] = 0.546 [115 times 2 + 8 times 62] = 396.396 Thus total at rest pressure po = 1/2 times 125.58 times 2 + 8/2 [68.14 + 396.396] = 1983.72 ans is 1.99 lb/ft