APPENDIX D: PRETEST OF GEOSYNTHETIC MATERIALS
Objectives
There were three objectives in conducting the pretest:
1. To rank the geosynthetics' performance with respect to resistance to
damage by tank traffic.
2. To "measure" the improvement to damage resistance by tank traffic due
to covering geosynthetics with 15 cm (6 in.) of "fill."
3. To rank the geosynthetics' performance with respect to reinforcement of
weak soil to improve trafficability. This was a secondary objective, and
we knew that achieving it would be difficult at the time we planned the
tests; indeed this turned out to be correct.
Date, location, and site conditions
The pretests were conducted on 16 and 17 March 1995. The soil was fine
sand in a "loose" state; it had frozen overnight (on 16 March), and had
relatively low moisture content on the surface. It was completely thawed at the
time of construction, was rutted, and was easily rutted more by construction
traffic.
Test sections
Two test sections were constructed. One consisted of "bare" geosynthetics
lying on the ground. The other was the same geosynthetics covered with 15 cm
(6 in.) of bank run gravel available on base. For both test sections, six different
geosynthetic products were laid in 6.1-m (20-ft) lengths in a row on top of the
sandy soil, with about 1.5-m (5-ft) spacing between the ends. The test sections
were parallel to each other with about 1.2 m (4 ft) between them. The bare
geosynthtic products were given numbers 1 to 6, and were laid north to south
from number 1 to 6; the covered products were laid south to north from
number 1 to 6. The products numbers were (see Table 2 in main body of the
report for the project description) as follows:
1
2
3
4
5
6
GTF 300
Polyrock
Geogrid overlain
Double-sided
TS1000
Geogrid
with TS 1000
geonet
Test section construction
No site preparation was done, and material was placed on rutted sandy soil,
having ruts up to 20 cm (8 in.) deep. The surface was very uneven. The
materials were very easy to lay out; most could be carried by hand by two
people. The double-sided geonet was an exception--it required a SEE to be
moved around.
When the gravel was placed, the dump truck drivers were asked not to
drive directly onto the materials. They found this difficult to do and short
sections of the products (up to 1.2 m [5 ft] long) were driven on anyway.
However, there was no apparent damage.
Grading of the thin layer of gravel resulted in visible damage to some
materials--the center of the material was nicked and the edges were exposed.
The grading damage made it obvious that driving dump trucks on the sections
with little cover caused the materials to deform such that they were depressed
into the wheel tracks and bulged upward in between the wheels. Post-
construction excavation of trenches across the material showed that the actual
cover thickness ranged from 2.5 to 20 cm (1 to 8 in.).
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