Table 2. Summary of maxi-
80
mum frost penetration at all
December:
thermocouple sites.
Mean = 71
70
Standard Deviation = 37
Maximum frost
March:
60
Mean = 33
penetration depth
Standard Deviation = 16
Thermocouple
(mm)
50
site
String A
String B
40
10
230
230
20
510
500
30
30
460
460
40
460
460
20
10
FIELD TESTING DATA ANALYSIS
0
Clegg impact hammer results
psi
25
50
75
100
125
150
175
200
kPa
172
345
517
689
861
1033
1206
1378
From information provided by NED, the
Unconfined Compressive Strength
minimum allowable unconfined compressive
a. Site 1.
strength limit was 30 psi (207 kPa). The uncon-
fined compressive strength values obtained
45
from the Clegg hammer were plotted for each
December:
40
Mean = 307
sampling location for both the December and
Standard Deviation = 133
March:
March testing programs. Appendix B contains
35
Mean = 170
Standard Deviation = 138
all of the data from the Clegg hammer tests.
30
As shown in Figure 12, the unconfined
25
compressive strength of site 1 is variable in
December when compared to March. How-
20
ever, most measurements are above the 30-psi
15
limit. In March, the variability is reduced and
10
approximately 50% of the data points fall be-
low the 30-psi limit. Sites 2 and 3 were also
5
both variable in unconfined compressive
0
strength. Both sites showed a reduction in
50
100 150 200 250 300 350 400 450 500 550 600
psi
345
689 1034 1378 1723 2067 2412 2756 3101 3445 3790 4134
kPa
strength from December to March, yet most
Unconfined Compressive Strength
values still remained above the 30-psi cutoff
b. Site 2.
(Fig. 11b and 11c).
60
Another way to view the data is by using a
December:
histogram for the unconfined compressive
Mean = 116
Standard Deviation = 57
50
strengths for December and March (Fig. 13ac).
March:
Mean = 62
Table 3 provides a summary of the statistical
Standard Deviation = 27
data.
40
For site 1, the mean unconfined compres-
sive strength for the December data are 71 psi
30
(489 kPa) with a standard deviation of 37 psi
(255 kPa). Testing results from March yield a
20
mean unconfined compressive strength of 33
psi (227 kPa), a reduction of approximately
10
50%. The values for the coefficient of variation
for Site 1 are 52% and 48% for December and
0
125 150 175 200 225 250 275 300
psi
25
50
75
100
March, respectively. The coefficient of varia-
861 1034 1206 1378 1550 1723 1895 2067
kPa
172
345
517
689
tion is high, and it represents the spatial vari-
Unconfined Compressive Strength
a. Site 3.
ability of the strengths found at the site. The
March data show that a deterioration of
Figure 13. Histograms showing shift in unconfined compressive
strength occurred during the freezing season.
strength.
Site 2 shows a similar downward shift in
strength, changing from a range between 250
9
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