Underground Infrastructure - February 2023 - 38

CIGMAT Report
Example Study: Field Compaction
Verifi cation Using New Surface Penetrometer
(SP-CIGMAT) During Construction
For site investigation, insitu tests are increasingly used to
determine the soil properties for geotechnical analysis and
design. Penetrometers evolved from the need to acquire data
on subsurface soils that were not sampled easily by any other
means. Hence, static and dynamic penetration resistances
have been used to classify and characterize subsoils.
Compaction characteristics of soils (three-phase materials),
depend on several factors, including soil type, moisture
content and compaction energy. Since the 1930s, numerous
laboratory and fi eld investigations have att empted to
understand the principles of compaction. Many researchers
have tried to develop correlations to predict the laboratory
compaction parameters by simulating the standard Proctor
compaction test, using a smaller compaction apparatus, or by
performing mathematical modeling.
Correlations are important in estimating the engineering
properties of compacted soils, based on properties shown
in FIGURE 11. Index tests can be easily performed and are
required for cohesive soils in all exploration programs. It is,
therefore, useful to estimate the engineering properties of
soils by using other, easily obtained, soil parameters.
Based on past studies, with an increase in the compactive
eff ort, the maximum dry unit weight increases and is accompanied
by a decrease in the optimum water content. Th ese changes
tend to be less pronounced with each additional increment
in energy and fi nally level-off , where further increase in dry
unit weight becomes negligible with higher compactive eff ort.
As shown in FIGURE 12, a soil at Point #1 or Point #2 could
be compacted using diff erent methods to reach Point #3,
where the dry density and moisture content are the same. For
example, Point #3 could be on the wet side of optimum on the
compaction curve for Path 1 and on the dry side for Path 2.
Hence, for Point #3, the mechanical properties will be based
on the energy/stress path the soil was subjected to during compaction.
Although the same dry density and moisture content
were achieved, the soil structure in the compacted soil will be
diff erent, based on the energy used for compaction.
Field Compaction Quality
Engineered soils are compacted to be used as fi ll materials for
embankments, pavement subgrades, earth dam construction,
and retaining wall backfi lls. When the fi ll materials are used
in the fi eld, there should be a method to achieve the required
quality, as shown in FIGURE 13 (acceptable region). Because
of that, the laboratory-determined properties are used in quality-checking
and -assurance work.
In theory, a fi eld inspector can rapidly determine if a soil
layer meets the specifi ed compaction criteria (dry density
and/or moisture content) without obtaining a soil sample for
laboratory Proctor compaction testing.
Quality control procedures usually include the fi eld measurement
of dry unit weight (γd/Field
laboratory maximum density (γd/Lab
) and comparison of the
) values that are expected
to be att ainable in the fi eld for the material and the applied
compactive eff ort, based on laboratory compaction tests.
Th e ratio (γd/Field
)/(γd/Lab
FIGURE 11: Major components in field compaction
) = RC (usually expressed as a
percentage) is the relative compaction. It is oſt en used as the
FIGURE 12: Compacted soil properties depend on the energy/stress
path of compaction.
38 FEBRUARY 2023 | UndergroundInfrastructure.com
FIGURE 13: Typical acceptable zone for compacted soils.
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