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Laboratory investigation of seismic effects of nanoparticle dispersions in saturated
granular media
Étude en laboratoire des effets sismiques des dispersions de nanoparticules dans les milieux
granulaires
Luke B.
University of Nevada Las Vegas, Las Vegas, Nevada, USA
Werkema D.
US Environmental Protection Agency, Las Vegas, Nevada, USA
Andersen S.
US Environmental Protection Agency and University of Nevada Las Vegas, USA,
ABSTRACT: Nanomaterials used in industrial applications and consumer products are widespread, thereby increasing the likelihood
of unintended environmental release. The fate and transport of nanoparticles in the environment and their effects on the environment
and human health are not well understood. This research investigates the potential to use seismic methods for such fate and transport
studies. A test cell using piezoceramic bender elements was constructed to investigate how nanoparticles dispersed in the pore fluid of
a saturated glass bead medium affect seismic wave propagation. Test cell design addresses optimal seismic wave propagation,
uniformity and repeatability of the placement of the granular media and uniformity of fluid flow. Time histories were produced from
two tests optimized for shear wave propagation. The first (baseline) test used deonized (DI) water. This test demonstrated the need to
stabilize the sample before making measurements by first flushing several liters of liquid through the system. The second test,
conducted on a new sample, used a solution of 0.05% nano Zinc Oxide (nZnO) in DI water after first flushing with DI water.
Comparison of results between the two tests shows only weak repeatability between test specimens. Despite this, results of the second
test still indicate a significant change in response in the presence of nZnO, particularly in signal amplitude. Studies are ongoing to
increase experimental reliability and sensitivity, and to more closely approximate expected field conditions.
RÉSUMÉ : Les nanomatériaux utilisés dans les applications industrielles et produits consommation sont très répandus ; il est donc
probable que ces substances se retrouvent disséminées dans l’environnement. Le destin et le transport des nanoparticules dans
l’environnement et leurs effets sur l’environnement méritent un étude approfondie. Cet article étudie la possibilité d'utiliser des
méthodes sismiques pour étudier ces effets. Une cellule a été construite pour voir comment les nanoparticules dispersées dans le fluide
interstitiel du verre change la propagation d’ondes. La conception de la cellule d’essai permet d’étudier la propagation des ondes
sismiques, le positionnement des milieux granulaires et l’uniformité de l’écoulement du fluide. Les temps de parcours de la
propagation des ondes sismiques dans une dilution d’oxyde de zinc nano 0,05 % (NZnO) dans une matrice de billes de verre sont
présentés et comparés à ligne de base. Nous avons trouvé une légère réduction de la vitesse de cisaillement et de compression en
présence de NZnO par rapport aux valeurs initiales. Nous proposons des études plus complexes qui se rapprocheraient des conditions
dans la nature.
KEYWORDS: nanoparticles, seismic, fate and transport, piezoceramic, bender elements.
1 INTRODUCTION
The use of nanoparticles in industrial applications and consumer
products has become widespread and continues to grow. As
applications of nanoparticles increase, so does the likelihood of
unintended environmental release, including the possibility of a
large-scale spill event. The fate and transport of nanoparticles
dispersed in the environment are largely unknown (Conlon,
2009; Klaine et. al., 2008), and their effects on the environment
and human health are also not well understood. Consequently,
methods are needed for detecting, characterizing, and
monitoring subsurface transport of nanoparticles. The capability
of electrical geophysical methods has shown some promise in
the spectral induced polarization (SIP) response to select
nanoparticles in saturated sand laboratory columns (Joyce et.
al., 2012). This paper investigates the seismic response to
nanoparticles in a similar laboratory setting, in order to
complement the SIP results and evaluate another geophysical
method.
We have developed a test cell that uses piezoceramic bender
elements to investigate how nanoparticles dispersed in the pore
fluid of a glass bead matrix can affect seismic wave propagation
characteristics. To minimize chemical interactions between the
granular medium and the nanoparticle solution and to provide
uniform grain morphology, non-reactive glass beads are used
for the granular medium. Seismic wave characteristics (spectral
content, travel time, signal amplitude) can be scrutinized for
distinguishing characteristics. Results may suggest whether
seismic methods are suitable for nanoparticle fate and transport
tudies.
s
This paper reports on the test cell design and development
of experimental procedures. Some preliminary travel time and
signal amplitude results using 0.05% nZnO solution are
included.
2 TEST CELL DESIGN AND TESTING PROTOCOLS
The test cell design is based on preliminary work by Rajabdeen
et al. (2012). The sample or experimental treatment housing is
a translucent 15.2-cm inner-diameter PVC cylinder with custom
end caps that are fitted with piezoceramic bender elements
(Figure 1). The bender elements serve as seismic transmitter
and receiver. The elements used in this study are two-piezo
layer transducers made with PSI-5A4E piezoceramic (a Lead
Zirconate Titanate (PZT) piezoceramic), parallel-poled, nickel
electrodes and using brass center reinforcement (Piezo Systems
Inc.).
The bender elements are 12.7 mm square and 0.5 mm thick.
Elements are potted in vinyl caps using epoxy which are placed
inside small-diameter PVC tubes that pierce and affix to the
centers of the end caps (Figure 1). This configuration is
intended to be robust while also creating impedance traps to
encourage transmission of seismic energy through the sample
rather than through the test apparatus. The cantilever length
(protrusion into the sample) is 4 mm, approximately one-third
the length of the element. A short cantilever length reduces
dependency of the system resonance frequency on the sample
matrix properties (Lee and Santamarina, 2005). The bender
elements are installed in-plane such that the S-wave energy
propagates along a direct, straight-line path while the strongest
P-wave arrival at the receiver would be reflected from the
cylinder walls (Figure 1). The test cell design integrates the
same considerations of signal attenuation and near-field effects
that have been applied to bender-element testing in oedometers
