Soil Friction Angle (deg)
EXAMPLE PROBLEMS Uplift Capacity
Shallow Anchor in Sand
Given the situation shown in Figure EX-1. Using equation 31:
Interpolating from Table 3, Fq = 30.06.
ku = 1.3 (Figure 5).
Qu = 5164+6021 = 11,185 lbs FS = 2.5
Qallow = 11,185 = 4474 lbs = 4.5kips
If the water surface were at the ground surface, then:
k tan
Qu = 5902 lbs FS = 2.5
Qallow = 5902/2.5 = 2361 lbs = 2.4 kips
Deep Anchor in Sand
Given the situation shown in Figure EX-2. Using equation 31:
pcf
Fq* = 50 (Figure 8)
Qu = 17181+10737 = 27918 lbs FS = 2.5
Qallow = 27918/2.5 = 11,167 lbs = 11.1 kips
If the water surface were at the ground surface, then:
Qu = 14730 lbs
Shallow anchor in Clay
Given the situation shown in Figure EX-3. Using equation 38
Fc = 9
Deep anchor in Clay
Bearing Capacity of a Helical Pile in Com-pression
Anchor in Sand (Figure EX-5)
c = 0
Anchor in Clay (Figure EX-6)
16
Lateral Capacity of a laterally Loaded Helical Pile in Medium Clay Assume the situation is as shown in Figure EX-7. Also assume:
Load = 40 kN
c = 1000 psf = 48 kPa Shaft Properties:
L = 8 ft = 2.4 m
2 inch square outside dimension wall thickness = 05 inch
Check to see if buckling will be a concern.
From Table 4, soil is a medium clay.
Using Figure 13, situation plots significantly below is medium clay line, therefore, buckling is not a concern.
Lateral Capacity of a Laterally Loaded Helical Pile in Soft Clay
Assume the situation is as shown in Figure EX-7.
Also assume:
Load = 40 kN c = 400 psf = 19 kPa Shaft Properties:
L = 8 ft = 2.4 m
2 inch square outside dimension
Check to see if buckling will be a concern.
From Table 4, soil is a soft clay.
Using Figure 13, situation plots near the soft clay line, therefore, buckling is a concern.
Helical shaft properties:
Ep = 30 106 psi = 20.7 107 kPa I = π(do4 -di4)/64 = 4.8 10-7 m4 From Table 5 assume nh = 500 kN/m4
Assume u* = 15 mm = yield deflection
Using equation 6 from Table 6
Using equation 6 from Table 7
mm
Using Equation 6 from Table 7
m -kN 359 M =
M 1.09 M P =
P
cf 0.72 cf
o
max
max
Lateral Capacity of a Laterally Loaded Helical Pile in Overconsolidated Clay Assume the situation is as shown in Figure EX-7. Also assume:
Load = 40 kN
c = 2000 psf = 96 kPa Shaft Properties:
L = 8 ft = 2.4 m
2 inch square outside dimension wall thickness = 0.5 inch
Check to see if buckling will be a concern.
From Table 4, soil is a stiff clay.
Using Figure 14, situation plots to the right of the stiff clay line, therefore, buckling is not a concern.
Helical shaft properties:
Ep = 30 106 psi = 20.7 107 kPa I = π(do4 -di4)/64 = 4.8 10-7 m4
m -kN 0.519 P =
0.9271 M =
cf cmax
Assume u* = 15 mm = yield deflection
Using equation 2 from Table 6
Using equation 2 from Table 7
mm
Determine the maximum moment.
Using Equation 2 from Table 6
Since Mcmax <Mo, part of soil is yielding.
Using Equation 2 from Table 7
M
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