Table 3. Tensile modulus values of geotextiles at 5% strain and at failure based on informa-
tion in Geotechnical Fabrics Report (1996).
Construction,
K at 5% strain
K at failure
mass/area
(kN/m)/(lb/in.)
(kN/m)/(lb/in.)
(g/m2)/
(oz/yd2)
MD
XD
MD
XD
Product
Amoco 2044
W-PP, na
420/2400
760/4340
700/4000
875/5000
Carthage FX-400MF
W-PP, 427/12
386/2206
456/2606
542/3098
783/4475
Contech C-300
W/S-PP, 200/6
174/994
210/1200
306/1749
383/2186
Huesker Comtrac 800
W-PET, 1430/42
7200/41150
800/4572
7910/45206
667/3810
Linq GTF 550T
W-PET, na
404/2309
404/2309
876/5006
876/5006
Linq GTF 1000T
W-PET, na
1050/6000
1050/6000
1402/8012
1402/8012
Synthetic Industries
W/S-PP, 150/4
174/994
192/1097
233/1333
300/1715
Gtx. 200ST
Synthetic Industries
W/C-PP, 440/13
384/2195
454/2595
500/2858
583/3334
Gtx. 4 4
TNS W300
W-PP, 203/6
100/570
280/1600
290/1657
310/1772
USA Spantex 5710
K-PET, 2566/76
8000/45720
4000/22860
10000/57150
4167/23814
Webtec, TTHPG-50
W-PP, na
200/1143
220/1257
267/1524
260/1486
Webtec, TTHPG-57
W-PP
700/4000
700/4000
538.5/3078
487.5/2786
Notes: na = not available, W = woven, K = knitted, PP = polypropylene, PET = polyester, MD = machine direction, XD
= cross-machine direction.
the geotextiles when they are being used and to
Giroud and Noiray (1981) and from calculations
relate them to the values measured in tensile tests.
performed for this work. There is a difference be-
tween the curves generated for Figure 13 and those
from Giroud and Noiray (1981) for the 450 kN/m
geotextile being used for the 480 kPa tire pressure.
COMPARISON OF GIROUD AND NOIRAY
This difference is estimated to be about 10% at the
METHOD WITH ARMY METHOD
very lowest values of aggregate thickness. The
The tensile reinforcement advantages offered
reason for this discrepancy is unknown.
by high-strength geotextiles may offset the in-
creased cost. Therefore, the currently used Army
Stress distribution through the aggregate layer
design technique is compared with the design
Figure 14 shows the soil strength vs. aggregate
technique of Giroud and Noiray (1981) in this sec-
thickness curves for both design techniques with-
tion. Design curves provided in Barenberg et al.
out geotextiles for dual wheels on a single axle
(1975) and Giroud and Noiray (1981) for static
with wheel loads of 60 and 115 kN (13,500 and
loading were reconstructed to verify that the cal-
25,850 lb) and tire pressures of 414 kPa (60 psi).
culation techniques used for this work are accu-
These represent 10-ton and 20-ton trucks (e.g.,
rate. Design curves for the loading imposed by
Table 1). The Barenberg et al. (1975) method is more
typical military vehicles using each design method
conservative at these loading conditions, and this
are also presented to demonstrate potential aggre-
stems from the load distribution assumptions per-
gate savings by use of the Giroud and Noiray
taining to the spreading of the load beneath the
(1981) method.
wheels. Table 4 shows the maximum vertical stress
at various depths below the load for a wheel load
of 115 kN and contact pressure of 414 kPa using
Validation of calculation techniques
Design equations were programmed using
the Boussinesq stress distribution beneath a cir-
Mathcad 6.0 (Mathsoft 1995) to generate design
cularly loaded area (i.e., Newmark 1942) and the
curves. Details are given in Appendix B. Figure 11
trapezoidal stress distribution beneath a rectan-
shows the static load design curves from
gular load used by Giroud and Noiray (1981).
Barenberg et al. (1975) and points calculated for
Barenberg et al. (1975) used the Boussinesq
this work to verify the calculations. Similarly, Fig-
stress distribution because experimental and field
ures 12 are 13 are static load design curves from
work of others show that stress distribution
13
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