Chap. 20 Piles: Serviceability Limit States
20.1 A 16 inch diameter, 75 ft long drilled displacement pile is made of grout with f’c = 5000 lb/in2.
A steel ratio of 0.04 is to be used in the upper 30 ft, and a steel ratio of 0.001 for the remainder of
the pile. Compute the modulus of elasticity for the upper and lower portions of this pile.
Solution
29,000,000lb/in
s
E=
Upper 30 ft
Chap. 20 Piles: Serviceability Limit States
20.2 The axial compressive load in the pile described in Problem 20.1 is 200 k at the top of the pile
and varies linearly to 20 k at the bottom of the pile. Compute the settlement at the top due to
elastic compression.
Solution
Total
Chap. 20 Piles: Serviceability Limit States
20.3 In Example 20.1, the load–settlement curve for side friction is much steeper than that for toe
bearing. Is this to be expected? Explain.
Solution
Chap. 20 Piles: Serviceability Limit States
20.4 An HP14x102 pile is to be driven to a depth of 48 ft. The side friction capacity,
ns
fA
∑
is 320
k and the toe bearing capacity,
nt
qA
′
, is 110 k. The expected service load will be 142 k. Using
the Fleming simplified method, compute the expected settlement. See Table 21.1 for pile section
properties. Assume fn is constant along the length of the pile.
Solution
Chap. 20 Piles: Serviceability Limit States
20.5 Using the pile described in Problem 20.4 and a spreadsheet, develop a plot of settlement versus
applied load. Consider loads from 0 to 280 k.
Solution
Chap. 20 Piles: Serviceability Limit States
20.6 A 300 mm diameter steel pipe pile with 10 mm wall thickness is to be driven to a depth of 15 m.
The side friction capacity,
ns
fA
∑
is 750 kN and the toe bearing capacity,
nt
qA
′
, is 210 kN.
The expected service load will be 310 kN. Using the Fleming simplified method, compute the
expected settlement. Assume fn is constant along the length of the pile.
Solution
2
9110mmA=
Chap. 20 Piles: Serviceability Limit States
20.7 Using the pile described in Problem 20.6 and a spreadsheet, develop a plot of settlement versus
applied load. Consider loads from 0 to 600 kN.
Solution
Chap. 20 Piles: Serviceability Limit States
20.8 A group of 25 prestressed concrete piles is arranged in a 5×5 grid. Each pile has a 12×12 inch
cross–section and is 63 ft long. The piles are placed 30 inches on center, and a 4 ft thick pile cap
connects these piles. The soil profile consists of a silty sand to a depth of 85 ft, underlain by very
dense sands and gravels. The silty sand has a constrained modulus of 1,200,000 lb/ft2. Develop
a plot of load vs settlement for this pile group. Consider loads from 0 to that load which
produces 2 inches of settlement. Ignore the contribution of elastic compression.
Solution
Use equivalent footing at a depth of 42 ft below the bottom of the pile cap