Applicability for Army use on
ALTERNATIVE METHOD PRESENTED BY
thawing soils
GIROUD AND NOIRAY
The design curves supplied in TM5-818-8 (Fig.
1 through 3) apply to vehicles with a 552 kPa
Giroud and Noiray (1981) developed a design
(80 psi) tire pressure, for single and dual wheel
method for geotextile placement between the ag-
loads varying from 22.24 to 88.96 kN (5,000 to
gregate and subgrade of unpaved roads based on
20,000 lb). Since TM5-818-8 does not list typical
bearing capacity theory for static loading. The
wheel loads for Army vehicles (nor does U.S.
method accounts for the load support and soil
Army Field Manual FM5-430-00-1), some are pro-
confinement provided by the geotextile itself and
vided for vehicles most likely to be used on
is presented as a set of curves for dual wheels on a
low-volume roads or trails (Table 1). The maxi-
single axle, with an axle load of 80 kN (18,000) at
mum wheel load for tandem axles listed in Table
various rut depths (Fig. 6 and 7). The curves are
1 was determined by multiplying the total load
used to determine aggregate thickness without
geotextile (ho′) and reduction of aggregate thick-
on the rear axles by 0.60 (e.g., Giroud and
ness with geotextile (∆h) for geotextiles with dif-
Noiray 1981) then dividing by two. For the 20-ton
ferent values of tensile modulus, K. The Giroud
dump truck (three rear axles), the maximum wheel
and Noiray (1981) design method was chosen for
load was estimated by multiplying the total
comparison with the method now used by the U.S.
load on the rear axles by 0.70 then dividing it
Army because it is widely used (e.g., Holtz et al.
by two.
1995) and because of its potential for cost savings
The maximum wheel loads listed in Table 1 for
by allowing thinner aggregate layers over the
Army vehicles are reasonably well-represented in
geotextile because it takes into account the tensile
Figures 1 through 3. Even though the tire pres-
properties of the geotextile.
sures in the figures are higher than the tire pres-
sures listed in Table 1, Barenberg et al. (1975) dem-
onstrated negligible difference in the design curves
Design example
Given the same vehicle and soil conditions de-
due to variation in the contact pressures ranging
scribed in the previous design example for the
from 552 to 1034 kPa (80 to 150 psi). This theory
method currently used by the Army, determine the
and design method assume that the subgrade is
aggregate thickness required with a geotextile of
uniform and that full plastic failure zones can de-
modulus K of 100 kN/m (570 lb/in.) and without
velop, the depth of which depends on the geom-
a geotextile. Conditions: 80 kN load on a dual-
etry and magnitude of the loading. Thus, this
wheel single axle, soil cohesion of 52 kPa (7.5 psi),
method was not intended for shallow thaw lay-
approximately 100 passes of the vehicle, tire infla-
ers, and it would be conservative to use this
tion pressure of 552 kPa (80 psi), and a tolerable
method for shallow thawed layers. Bounds on the
rut depth of 0.3 m (12 in.). Although Figure 6 is
depth of the thawed layer for full development
constructed for a tire inflation pressure of 480 kPa
of the plastic zone are discussed in the following
(70 psi), little difference in aggregate thickness is
section.
Table 1. Traffic loading data for Army vehicles (Foss 1983).
Gross vehicle
Load on
Maximum
Tire
Ground
Vehicle/axle
weight
rear axles
wheel load
pressure
clearance
type
(kN/lb)
(kN/lb)
(kN/lb)
(kPa/psi)
(m/in.)
HMMWV
33.31/7,489
21.65*/4,869
10.83/2,434
241/35
0.41/16
M939 (6 6) 5-ton cargo truck
146.80/33,000
138.59/31,156
41.58/9,346
345/50†
0.30/12
HEMTT, M985
302.48/68,000
169.0/38,000
50.7/11,400
483/70†
0.30/12
M125 10-ton truck
289.14/65,000
187.94*/4,225
56.4/12,680
Not available
0.52/20
Articulated 8 8
Not available
258.0/58,000
77.4/17,400
414/60
0.30/12
M917 20-ton dump truck
324.30/72,906
324.30/72,906
113.51/25,520
414/60
Not available
Notes:
*No rear axle load was given; it was assumed that 65% of the gross vehicle load is applied on the rear axles.
†From Jeffrey Stark (personal communication, CRREL, 1997).
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