I
C
L
Surface
Figure 11. Cross section of pavement (after Lui
Pipe
Course
et al. 1983).
A
D
B
C
Base Course
Subgrade
Original Ground Surface
Stage 1:
dx
x
0 < U ≤ 50%
A
S + 2U
T = 2US - S2 ln
.
D
S
t + dt
t
Stage 2:
H
50% < U ≤ 100%
2S - 2US + 1
S +1
T = S + S ln
- S2 ln
B
L tan α
α
(2 - 2U )(S + 1)
S
C
where U = drained area/total area
Stage 1 (U ≤ 50%)
A
H
(Fig. 12)
S = slope factor =
L tan α
D
t
2tkH
T = time factor =
cnL2
dh
H
0.8
c = 2.45 -
h
3
S
t + dt
L = one-half width of pavement
B
L tan α
α
H = thickness of base course
α = angle of slope of base layer
C
t = time
Stage 2 (U ≥ 50%)
k = permeability of base course
Figure 12. Casagrande and Shannon model for base
n = porosity of base course.
course drainage.
U.S. Standard Sieve Numbers
Hydrometer
6" 4"
2"
1"
10
40
200
3/8"
100
0
80
20
60
40
k = 0.0035 cm/s (10 ft/day)
40
60
1.06 (3000)
0.35 (1000)
20
80
0.039 (110)
100
0
100
10
1
0.1
0.01
0.001
Grain Size (mm)
Gravel
Sand
Figure 13. Typical k values for
Cobbles
Silt or Clay
Coarse
Fine
C'rse
Medium
Fine
base course gradations.
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