Underground Infrastructure - February 2023 - 39

CIGMAT Report
TABLE 5: Summary of physical properties of soils
Soil Type
CL
Mean
Standard deviation
COV (%)
LL
42
2.2
5.3
criterion for compaction, where (γd/Lab
PL
16
2.2
13.8
PI
26
2.2
11.6
) is the maximum dry
unit weight of the soil for a given laboratory compaction standard.
Also, several other methods have been used to control
the fi eld compaction, one of which is the air voids method
(less than 10%) of evaluating the fi eld compaction.
As is well-known, one of the most important parameters
in a pavement management system (PMS) is both the
functional and structural capacity of the pavement network.
Currently, there is no standard fi eld test to determine the
strength of base and subgrade soils for construction quality
control/assurance purposes, although many transportation
agencies only use density and moisture measurement.
Th e falling weight defl ectometer (FWD), geogauge, dirt
seismic pavement analyzer (DSPA), and laboratory repetitive
triaxial tests have been used to determine the pavement
layer modulus. However, each method has limitations. As
many diff erent sets of layer moduli would satisfy the same
FWD defl ection bowl, practicing pavement engineers struggle
to identify the correct set. Also, the FWD oſt en is unable
to determine the extent of a weak base/subgrade layer, due
to a thick concrete layer that carries most of the load away.
Laboratory repetitive triaxial tests are seldom used to determine
the layer moduli for routine design or QC/QA tests
in current DOT environments. Seismic tests are quick and
easy, but the seismically determined modulus is very high
due to the high frequencies and miniscule loads used. Th e
geogauge is highly sensitive to the surface preparation, and
it only gives a composite stiff ness that includes all layers to
some uncertain depth.
Compacted soils are those where the insitu structure is
modifi ed by compaction. Th e main objective of compaction
is to improve the performance of a material by increasing its
strength, stiff ness and durability. Th ere are many situations
where compacted soils are used, such as constructing a new
embankment, road, earth dam, building foundation and retaining
wall back fi lls soils.
To inspect and verify the quality and construction of
compacted soils, nondestructive testing devices are extremely
att ractive, due to the rapidity in performing the tests.
Researchers have used dynamic cone penetrometer (DCP),
California bearing ratio (CBR) and falling weight defl ectometer
(FWD) for evaluating earth structures, backfi lls for pipelines,
pavements and subgrade soils.
Th e advantages of insitu testing include the disturbance is often
less than in sampling and testing, and results can be viewed
in real time and used to modify fi eld compaction procedure.
Specifi c Gravity
2.69
0.016
0.60
Remarks
Lesser variation in the soil properties compared to other
CL soils selected for the fi eld study. Also had less LL and
PI to other CL soils
FIGURE 14: Laboratory and field compaction results for a CL soil.
Objective, Methods
Th e objective of this study was to compare the diff erences in
fi eld and laboratory compacted CL soil and evaluate the performance
of a surface penetrometer (SP-CIGMAT) to characterize
the compacted soil during construction.
A fi eld test program was conducted to determine the compaction
of soil using the Caterpillar 815F (45,765-pound, 3.88foot
drum diameter and 3.25-foot drum width). About 200 cubic
yards of each CL soil was stockpiled on the site for testing.
Th e 16-foot-by-250-foot test pads were prepared by removing
the top 18 inches of native soil, placing a geotextile
layer at the bott om and refi lling it with borrowed soils that
were well-compacted to have leveled test pads.
Compaction of the several CL soils was studied for 8-inch
liſt s and unit weight, and moisture contents were measured
at a minimum of fi ve locations along the test pad aſt er each
pass of the 815F compactor. Compaction continued until the
measured unit weight approached an asymptotic level. For
each CL soil, compaction tests were performed for at least six
moisture contents.
At least 10 samples were randomly collected from each
CL soil stockpile to measure the physical properties. Th e results
are summarized in TABLE 5 for one CL soil selected for
this document.
Test results from the laboratory and fi eld compaction (FC))
studies for the selected CL soil are shown in FIGURE 14.
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