Geosynthetics February/March 2022 - 27

Where: h=required base thickness
(m); α=load distribution angle;
r=radius of load (equivalent to wheel
or dual wheel) (m); P=wheel load
(kN); Nc=bearing capacity factor;
cu=undrained cohesion of subgrade
soil (kPa) and m=bearing capacity
mobilization coefficient
Geosynthetics are incorporated
into this equation with the bearing
capacity factor, Nc, which is based
on the presence of geotextile or geogrid
reinforcement.
Nc=π no reinforcement
Nc=π + 2 geotextile reinforcement
Nc=3 " π " /2 + 1 geogrid reinforcement
(with geotextile separator)
Roadway Design and Performance Properties
Base Course MR Improvement Factor1
Traffic Benefit Ratio (TBR)2,3,4
Cyclic Tensile Modulus @ 2% Permanent Strain (Jcyclic) (MARV)
Interaction Coefficient (Ci)5
Pore Pressure Dissipation Ratio2
Average Dynamic Filtration Pore Size
Tensile Strength @ 2% Strain (MARV)
Tensile Strength @ 5% Strain (MARV)
Index Properties
Apparent Opening Size (AOS) (Maximum Roll Value)
Hydraulic Flow Rate (MARV)
Permittivity (MARV)
UV Resistance (at 500 hours exposure)
It was determined that the required
unreinforced thickness was 16 inches (406
mm) compared to 7 inches (178 mm) of
aggregate for the reinforced section using
TenCate Mirafi RS380i geotextile with the
properties displayed in Table 1.
The geotextile and aggregate section
increased the bearing capacity of the
soft, saturated soils, providing a surface
capable of supporting the intended loads
(Figure 7).
The reinforced system had an approximate
cost of $9.25/square yard including
the geotextile, aggregate and installation,
compared to $16.00/square yard for the
unreinforced system. This solution saved
40% or $560,000 for the 70,000 square
yards (58,530 m2) of stabilized roadways.
Guidance Document/Test Method
AASHTO R50-09
AASHTO R50-09
ASTM D7556
ASTM D6706
Measured
ASTM D6767
ASTM D4595
ASTM D4595
Test Method
ASTM D4751
ASTM D4491
ASTM D4491
ASTM D4355
Unit
-
-
MD
lb/ft (kN/m)
54406.0 (794.0)
-
-
microns
lb/ft (kN/m)
lb/ft (kN/m)
Unit
U.S. Sieve (mm)
gal/min/ft2 (L/min/m2)
sec-1
% strength retained
600.0 (8.8)
1800 (26.3)
1020.0 (14.9)
2256.0 (32.9)
Roll Value
40.0 (0.425)
75.0 (3056.0)
0.9
90.0
1Value determined from results of independent testing performed at Kansas State University in accordance with National Cooperative Highway Research Program (NCHRP) Report 512,
" Accelerated Pavement Testing: Data Guidelines, " and AASHTO R50-09, " Geosynthetic Reinforcement of the Aggregate Base Course of Flexible Pavement Structures. " Multiplier for unbound
granular material; for SG MR between 30.9 and 47.4 MPa (4.5 and 6.9 ksi).
2Value determined from results of independent testing performed at GeoTesting Express (Geocomp Corp.), " A Laboratory Evaluation of the Performance of TenCate Mirafi Geosynthetics in
Roadway Stabilization Applications-Georgia Silt Subgrade, " Sep. 1, 2011. 9-kip (40 kN) wheel load; SG CBR=1%; 12-inch (300-mm) crushed aggregate BC (CBR>25%); 3-inch (75-mm) rut depth.
3Value determined from results of independent testing performed at the Louisiana Transportation Research Center (LTRC), " Performance of Reinforced-Stabilized Unpaved Test Sections Built
over Native Soft Soil Under Full-Scale Moving Wheel Loads, " Transportation Research Record, Vol. 2511, 2015. Measured at 0.3-inch (8.6-mm) rut depth; peak pore pressure 6 inches (150 mm)
below geosynthetic.
4Value determined from results of independent testing performed at GeoTesting Express (GeoComp Corp.), " A Laboratory Evaluation of the Performance of TenCate Mirafi Geosynthetics in Roadway
Stabilization Applications-Montana Clay Subgrade, " Sep. 1, 2011. 9-kip (40 kN) wheel load; SG CBR=1.8%; 8-inch (200-mm) rounded aggregate BC (CBR>25%); 3-inch (75-mm) rut depth.
5Interaction coefficient value is for sand (SP) or gravel (GW) based on testing conducted by SGI Testing Services LLC. U.S. Patent 8,333,220 and 8,598,054.
TABLE 1 Performance and index properties of TenCate Mirafi RS380i
www.GeosyntheticsMagazine.com
27
MD
72907.0 (1064.0
0.89
1.6
O95-392 O85-328 O60-245 O50-195
CD
FIGURE 7 Stabilized access road with highstrength
geotextile
Design/Calibration Value
1.3
3.9/5.2/21.75
CD
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Geosynthetics February/March 2022

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