Following are the standard penetration numbers determined from a sandy soil in the field:
|
Depth (ft)
|
Unit weight of soil (lb/ft2)
|
N60
|
|
10
|
106
|
7
|
|
15
|
106
|
9
|
|
20
|
106
|
11
|
|
25
|
118
|
16
|
|
30
|
118
|
18
|
|
35
|
118
|
20
|
|
40
|
118
|
22
|
Using Eq. (3.30), determine the variation of the peak soil friction angle, f9. Estimate an average value of f9 for the design of a shallow foundation. (Note: For depth greater than 20 ft, the unit weight of soil is 118 lb/ft3.)