of the tank driver. Another tree of about the same
in Table A1f--thaw depths on the wooded trail at
size was removed on the morning of 22 March,
the end of trafficking (App. A).
also at the request of the driver.
On the morning of 22 March, a bulldozer traf-
Test section performance--
ficked the test sections to make repairs to the
vehicle mobility
turnaround locations at the end of the test area, to
The performance of each vehicle on each of the
the control sections, and to the chunkwood and
test surfaces and control was documented using
tire chips (bladed out the ruts), all of which were
the driver survey form querying the condition of
deeply rutted. There was no apparent damage
the vehicle, experience of the driver, how and
from the bulldozer to any of the test sections ex-
when there was any interference of the test sur-
cept for a 75-cm- (2.5-ft-) long tear in the double-
face with the vehicle, and how the test surface
sided geonet. Ruts formed over the Geonet and
affected the vehicle performance in terms of trac-
Polyrock (after 25 passes) were filled in with in-
tion, slipping, speed, handling, etc. An example
situ soil and some larger objects (e.g., rocks and
form is given in Appendix G. The driver's rating
logs). This provided minimal anchoring because
of the test surfaces along with driver comments is
there wasn't enough material mass to weight it
summarized in Table 5. Additional comments from
down, since the ruts were about 15 cm (6 in.) deep
the drivers were that some materials (such as the
at the maximum.
chunkwood and slash on the wooded trail) were
placed in locations with few adverse factors
Wooded trail
affecting their survivability (such as no steering
The wooded trail was first trafficked with 50
required, no standing water prior to construc-
passes of the M60 tank on 24 March 1995. Just
tion), while others were placed in positions where
prior to trafficking, a 22,500-L (6000-gal.) water
they were doomed to failure (such as poor width
truck made two passes applying water at an even
spacing of the tire mats on very soft soil and
rate along the test section for the purpose of en-
standing water on the wooded trail). Indeed, site
suring high moisture content conditions. On 25
variability analysis already discussed indicates
March 1995, several repairs were made to the
nonuniform conditions.
wooded trail, and trafficking continued with the
A NOGO condition (see App. H) is defined
HEMTT on 26 March 1995.
as a terrain or surface condition that results in a
vehicle becoming immobile. Additionally, condi-
Pentagonal loop trail
tions where the driver chooses not to proceed
The M60 trafficked the pentagonal loop trail in
further upon serious damage to the vehicle or
order to observe the behavior of various stabili-
surface, resulting in immobilization, are also
zation materials when a tank cornered on them.
considered NOGO situations. NOGO conditions
Fifty passes with the M60 tank were made on 25
occurred during the construction and testing of
March 1995. The weather was cloudy and cool.
the test surfaces as follows:
The soil was notably dry, especially compared to
the other test sections. The pentagonal loop trail
The M60A3 threw a track while rounding a
was not trafficked with the HEMTT.
corner on the wooded trail prior to construc-
tion of test sections.
Test section performance--durability
Tire chip pretest caused flat tires on the CJ5
Table E1 summarizes observations and test sec-
after only three passes (note: tires were pre-
tion performance and briefly discusses how each
viously in poor condition).
technique could be improved for future testing
Larger pieces of slash on the slopes had to be
and use. Detailed observations of each test sec-
removed to prevent interference and pos-
tion are contained in Appendix E. Left and right
sible throwing of the tank track (Fig. 12).
rut depths for each trail after HEMTT trafficking
Unanchored, bare polypropylene TS1000
are shown in Figure 11. As discussed in the site
geotextile on the wooded trail (16+50 to
characterization section, in most instances, stabi-
17+75) did not provide adequate flotation
lizing techniques cannot be ranked by directly
for the construction vehicles and was cov-
comparing rut depths, as stabilization techniques
ered with chunkwood after approximately
separated by any appreciable distance were con-
20 passes with 5-ton dump truck.
structed on virtually different subgrades. Just one
The 14+75 to 15+50 control section on the
of the many factors influencing rut depth is shown
wooded trail become impassable during con-
17
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