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| Titel |
GPR-based evaluation of strength properties of unbound pavement material from electrical characteristics |
| VerfasserIn |
Andrea Benedetto, Fabrizio D'Amico, Fabio Tosti |
| Konferenz |
EGU General Assembly 2013
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 15 (2013) |
| Datensatznummer |
250074981
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| Zusammenfassung |
| It is well known that inter-particle friction and cohesion of soil particles and aggregates
deeply affect the strength and deformation properties of soils, exerting critical effects on the
bearing capacity of unbound pavement materials. In that respect, considering that strength
characteristics of soil are highly dependent on particle interactions, and assuming a
relationship between electric properties (e.g. electric permittivity) and bulk density of
materials, a good correlation between mechanical and electric characteristics of soil is
expected.
In this work, Ground Penetrating Radar (GPR) techniques are used to investigate this
topic. Two GPR equipment with same electronic characteristics and different survey
configurations are used. Each radar operates with two ground-coupled antennae at
600 MHz and 1600 MHz central frequencies. Measurements are developed using
4 channels, 2 mono-static and 2 bi-static. The received signal is sampled in the
time domain at dt = 7.8125 Ã 10-2 ns, and in the space domain every 2.4 Ã 10-2
m.
A semi-empirical model is proposed for predicting the resilient modulus of sub-asphalt
layers from GPR-derived data. Basically, the method requires to follow two steps. Firstly,
laboratory tests are carried out for calibration, with the main focus to provide consistent
empirical relationships between physical (e.g. bulk density) and electric properties. The
second step is focused on the in-situ validation of results through soil strength measurements
retrieved by CBR tests and Light Falling Weight Deflectometer (LFWD). On the basis of
traditional empirical equations used for flexible pavement design, the following expression is
proposed:
-m
Ei = αj-
hj,i
j=1
where Ei [MPa] is the ith expected resilient modulus of the surveyed soil under the line of
scan, hj,i [m] is the ith thickness referred to the jth layer, and αj is a dielectric parameter
calibrated as a function of the relative electric permittivity.
The experimental setting requires the use of road material, typically employed for
subgrade and subbase courses. Different types of soil ranging from group A1 to A4 by
AASHTO soil classification system, are analyzed. As regards the laboratory experiments,
material is gradually compacted in electrically and hydraulically isolated test boxes. A large
metal sheet supports the experimental boxes, so that the transmitted GPR signal is totally
reflected. GPR inspections are carried out for any compaction step up to the maximum
density value available. Moreover, in-situ tests are carried out on targeted types of soil,
with grain size distribution and texture comparable to those analyzed in laboratory
environment.
The results of this study confirm a promising correlation between the electric
permittivities and the strength and deformation properties of the surveyed soils. Laboratory
analyses show that the relationship between the relative permittivity and the bulk density is
positive: the higher the density of the compacted soil sample, the higher the electric
permittivity of the medium. Analogously, in-situ validation presents a good comparison
between measured and predicted data. Percentage errors less than 20% demonstrate that a
reliable prediction of Young Modulus using this GPR-based approach can be achieved. |
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