Geosynthetics August/September 2019 - 29
Guide for Design of Pavement Structures
and enhanced layer coefficients to account
for the benefits of the geogrid, and complies with AASHTO R-50, Standard
Practice for Geosynthetic Reinforcement
of the Aggregate Base Course of Flexible
Pavement Structures. The coefficients
used in this application are based on laboratory and field testing of these specific
geogrids and should not be used with other
geogrids (Applied Research Associates Inc.
and Ryan R. Berg Associates 2013).
Once a preliminary design for the haul
road was developed, two test strips were
built: one using two 12-inch (305-mm)
layers graded aggregate base (GAB) with
two layers of multiaxial geogrid, and the
other using one 24-inch (610-mm) layer
of No. 2 stones and one layer of multiaxial
geogrid. The No. 2 stone was choked with
GAB to improve the rideability. The test
strips were trafficked with a fully loaded
tandem dump truck (gross vehicle weight
50,000 to 60,000 pounds [23,000 kg to
27,000 kg]) to observe rutting behavior.
The ruts observed in the first test strip
were approximately 3.5 inches (89 mm)
deep after fewer than 10 passes. The second test strip developed very shallow ruts
(0.5 inch [13 mm] or less). This experience with the haul road was then incorporated into the final pavement design.
Once the initial estimate of required
thickness for the final pavement was
established, the team considered other
site conditions that might affect the success of the design and adjusted accordingly. Two primary concerns were
addressed: variability in the strength of
subgrade soils across the project and
the potential effects of groundwater and
drainage. Constructibility of the pavement drainage system and how the drains
tied into the already-constructed storm
drain system were also considered.
To address the variability in soil
conditions, the primary concern was to
ensure that the MSL would maintain
maximum stiffness so that the surface
would remain stable. Stiffness in the layer
is established by the confinement and
interlock of the particles of granular fill.
Prior research has demonstrated that the
compacted granular fill above a geogrid
has both fully confined and partially confined zones, so as thicker granular layers
are used, confinement can be enhanced
using additional layers of geogrid. In
general, layers of multiaxial geogrid that
are spaced at approximately 12 inches
(305 mm) within the MSL are adequate to
maintain full confinement. The test strips
indicated that only one layer of geogrid
with the No. 2 stone provided adequate
support; therefore, in this case, it was
decided that the design would use one
layer of geogrid in the 24-inch (610-mm)
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Geosynthetics August/September 2019
Table of Contents for the Digital Edition of Geosynthetics August/September 2019
Geosynthetics August/September 2019 - Cover1
Geosynthetics August/September 2019 - Cover2
Geosynthetics August/September 2019 - 1
Geosynthetics August/September 2019 - 2
Geosynthetics August/September 2019 - 3
Geosynthetics August/September 2019 - 4
Geosynthetics August/September 2019 - 5
Geosynthetics August/September 2019 - 6
Geosynthetics August/September 2019 - 7
Geosynthetics August/September 2019 - 8
Geosynthetics August/September 2019 - 9
Geosynthetics August/September 2019 - 10
Geosynthetics August/September 2019 - 11
Geosynthetics August/September 2019 - 12
Geosynthetics August/September 2019 - 13
Geosynthetics August/September 2019 - 14
Geosynthetics August/September 2019 - 15
Geosynthetics August/September 2019 - 16
Geosynthetics August/September 2019 - 17
Geosynthetics August/September 2019 - 18
Geosynthetics August/September 2019 - 19
Geosynthetics August/September 2019 - 20
Geosynthetics August/September 2019 - 21
Geosynthetics August/September 2019 - 22
Geosynthetics August/September 2019 - 23
Geosynthetics August/September 2019 - 24
Geosynthetics August/September 2019 - 25
Geosynthetics August/September 2019 - 26
Geosynthetics August/September 2019 - 27
Geosynthetics August/September 2019 - 28
Geosynthetics August/September 2019 - 29
Geosynthetics August/September 2019 - 30
Geosynthetics August/September 2019 - 31
Geosynthetics August/September 2019 - 32
Geosynthetics August/September 2019 - 33
Geosynthetics August/September 2019 - 34
Geosynthetics August/September 2019 - 35
Geosynthetics August/September 2019 - 36
Geosynthetics August/September 2019 - 37
Geosynthetics August/September 2019 - 38
Geosynthetics August/September 2019 - 39
Geosynthetics August/September 2019 - 40
Geosynthetics August/September 2019 - 41
Geosynthetics August/September 2019 - 42
Geosynthetics August/September 2019 - 43
Geosynthetics August/September 2019 - 44
Geosynthetics August/September 2019 - 45
Geosynthetics August/September 2019 - 46
Geosynthetics August/September 2019 - 47
Geosynthetics August/September 2019 - 48
Geosynthetics August/September 2019 - 49
Geosynthetics August/September 2019 - 50
Geosynthetics August/September 2019 - 51
Geosynthetics August/September 2019 - 52
Geosynthetics August/September 2019 - Cover3
Geosynthetics August/September 2019 - Cover4
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