Geoscience Reference
In-Depth Information
16.9 Pavement reduction with geotextiles
•
The pavement depth depends on ESAs and acceptable rut depth.
•
Elongation of geotextile
=
ε
.
•
Secant Modulus of geotextile
=
k
.
Table 16.9
Typical pavement thickness reduction due to geotextile (adapted from Giroud and Noiray,
1981).
In situ
Maximum pavement reduction for acceptable rut depth
CBR
(%)
30-75 mm
250 mm
250 mm
250 mm
250 mm
250 mm
250 mm
(
10%)
(
7%)
(
5%)
(k
10 kN/m)
(k
100 kN/m)
(k
300 kN/m)
ε
=
ε
=
ε
=
=
=
=
0.5
175 mm
450 mm
300 mm
100 mm
150 mm
200 mm
300 mm
1
125 mm
250 mm
100 mm
0 mm
125 mm
150 mm
225 mm
2
100 mm
100 mm
0 mm
75 mm
125 mm
100 mm
3
40mm
30mm
30mm
30mm
30mm
4
0 mm
0 mm
0 mm
0 mm
0 mm
16.10 Bearing capacity factors using geotextiles
•
The geotextiles provide an increase in allowable bearing capacity due to added
localised restraint to the subgrade.
•
The strength properties of the geotextile often do not govern, provided the
geotextile survives construction and the number of load cycles is low.
•
Subgrade strength C
u
=
23 CBR for undisturbed condition.
•
Ultimate Bearing Capacity q
ult
=
N
c
C
u
.
Table 16.10
Bearing capacity factors for different ruts and traffic conditions (Richardson, 1997: Steward
et al., 1977).
Geotextile
Ruts (mm)
Traffic (passes of 80 kN axle equivalent)
Bearing capacity factor, N
c
Without
50
1000
2.8
<
<
>
100
<
100
3.3
With
50
1000
5.0
<
<
100
100
6.0
>
<
- During construction 50 to 100mm rut depth is generally acceptable.
- Dump truck (8m
3
) with tandem axles would have a dual wheel load of 35 kN.
- Motor Grader would have a wheel load approximately 20 kN to 40 kN.
-
Placement of the geogrid at the subgrade surface does not have a beneficial
effect. Grids perform better when placed at the lower third of aggregate.
16.11 Geotextiles for separation and reinforcement
•
A geotextile is used as separation and reinforcement depending on the subgrade
strength.
•
A geotextile separator is of little value over sandy soils.
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