special plates that could circulate tempera-
Table 1. Samples tested for resilient modulus.
ture-regulated fluid at the top and bottom.
Condition
The bottom porous plate allowed move-
Never
ment of any additional water required for
Thawed*
Material
Frozen
frozen
open system freezing. The fluid tempera-
Sandy lean clay subgrade (CL)
tures were set to allow freezing from the
4†
1206 (high heave)
4
24
top down at the rate of about 2.5 cm (1 in.)
8†
1232 (low heave)
8
18
per day. The specimens were frozen with a
**
surcharge of 3.4 kPa (0.5 lb/in.2 ) placed
Class 3 stockpile
5
4
on the upper cold plate; this weight simu-
6**
Class 6 stockpile
7
lates the weight of a 15.2-cm (6-in.)-
Total
24
42
thick asphalt concrete pavement surface.
* Same samples were tested in the frozen and thawed condition
After freezing was complete, the speci-
† Samples tested only in the thawed, undrained condition
men ends were trimmed to assure that they
** Thawed samples were tested at several moisture contents
were smooth and flat. For the subgrade
specimens, this was done by milling the
tested at room temperature. We refer to these as a
ends flat. For the base and subbase materials, we
"never frozen" specimens. Specimens of the low-
made a slurry of fine material that was placed in
heaving subgrade (1232) included replicates of
custom-made equipment similar to that used for
various moisture contents at a single density; for
capping concrete specimens with molten sulfur.
the high-heaving subgrade (1206), replicates were
The slurry was then frozen to the ends of the
made with variation in both moisture and density
specimen and milled flat and smooth.
conditions. A total of 66 specimens were prepared
Subgrade specimens tested at room tempera-
(Table 1).
ture without being frozen were molded at the speci-
fied moisture/density levels, trimmed with a knife,
Specimen preparation
and tested immediately. For the Sample 1232
The specimen size used for the subgrades and
subgrade, the density was held constant at about
the class 3 special subbase was 5.1 cm (2 in.)
1.76 Mg/m3 (110 lb/ft3) and the moisture content
diam. and 12.7 cm (5 in.) long. The coarser class 6
was varied from 13% to a saturated value of 20%,
special material was tested using specimens mea-
by weight (Table 2). For the 1206 subgrade, speci-
suring 15.2 cm (6 in.) in diam. and 39.4 cm (15.5
mens were prepared at three compactive efforts,
in.) in length. Gradation curves and other physical
with moisture contents intended to be at three
properties of these materials are in Bigl and Berg
conditions: optimum, 2% above optimum, and 2%
(1996a).
below optimum (Table 2).
Specimens that were tested in frozen/thawed
conditions were first molded at the specified mois-
Test procedures
ture/density condition, which was usually at opti-
The resilient modulus tests were conducted us-
mum as determined from the compaction testing.
ing repeated-load triaxial test procedures, the de-
The subgrade specimens were compacted with a
tails of which are described in reports by Cole et
CE-12 (Standard Proctor) compaction effort, while
al. (1985 and 1986). Testing was accomplished in
the class 3 special and class 6 special were com-
triaxial cells that were constructed to accommo-
pacted with a CE-55 (Modified Proctor) effort to
date the instrumentation used to monitor load and
approximate anticipated in-situ conditions (Table
deformation (Fig. 1). Separate cells were used for
2). The specimens were then prepared in a manner
the 5.1- and 15.2-cm (2- and 6-in.)-diam. specimens.
similar to the procedure used in the frost suscepti-
The triaxial cells were designed so that the cell base
bility test (Chamberlain 1987). They were set on a
could be removed from the rest of the major cell
special base with a porous stone and saturated
components. In this way, a specimen could remain
from the base up with a constant head water sup-
on its base while the remainder of the assembly was
ply. Once saturated, the specimens and their po-
used on other specimens in a rotating sequence. A
rous-stone bases were positioned with two other
miniature, high-precision load cell mounted in the
2
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