1663
In Situ Assessment of the Nonlinear Shear Modulus of Municipal Solid Waste
Évaluation in situ du module non linéaire de cisaillement des déchets solides municipaux
Zekkos D., Sahadewa A., Woods R.
University of Michigan, Ann Arbor
Stokoe K.
University of Texas, Austin
Matasovic N.
Geosyntec Consultants
ABSTRACT: Assessment of dynamic properties of Municipal Solid Waste (MSW) is required for seismic response analyses of
existing MSW landfills in areas of moderate to high seismicity. While material properties such as shear wave velocity and unit weight
can be readily measured, assessment of nonlinear dynamic properties of MSW has, to date, been restricted to specialty laboratory
testing of reconstituted MSW specimens and back analysis of recorded earthquake response. Both approaches have limitations. In this
paper, the results of direct in-situ measurements of both small-strain shear modulus and the nonlinear shear modulus reduction
relationship are presented. The measurements were performed at a landfill in Austin, Texas, using two mobile vibroseis shakers. In
situ tests were performed at two locations. The vertical static load imposed by the vibroseis was varied to evaluate the effect of
vertical stress on the dynamic properties of the MSW. Dynamic testing was performed at increasing horizontal loads inducing small to
large strains in the MSW. Shear strains ranging from 0.0002% to 0.2% were induced by the shakers allowing the development of in
situ shear modulus reduction curves over a large strain range. The effect of waste composition was also assessed in situ.
RÉSUMÉ : L’Évaluation des propriétés dynamiques des déchets solides municipaux (MSW) est nécessaire pour les analyses de
réponse sismique des décharges de DSM existants dans les zones de sismicité modérée à élevée. Bien que les propriétés matérielles
telles que la vitesse des ondes de cisaillement et poids unitaire peut être facilement mesurée, l'évaluation des propriétés dynamiques
non linéaires de DSM a, à ce jour, été limitée à des tests de laboratoire spécialisés de spécimens reconstitués de DSM et de l'analyse
inverse de la réponse au tremblement de terre enregistré. Les deux approches ont leurs limites. Dans cet article, les résultats des
mesures directes in situ de deux modules de cisaillement a faible contrainte et la relation non linéaire de la reduction du module de
cisaillement sont présentés. Les mesures ont été effectuées dans une décharge à Austin, au Texas, utilisant deux gros camions
secoueurs vibrosismiques. Les essais in situ ont été effectuées à deux endroits. La charge verticale statique imposée par les camions
secoueur a été modifiée afin d'évaluer l'effet de la contrainte verticale sur les propriétés dynamiques de la DSM. Des essais
dynamiques ont été réalisés tout en augmantant les charges horizontales qui ont cree des deformations variant entre des petites et des
grandes déformations dans le DSM. Des déformations de cisaillement allant de 0,0002% à 0,2% ont été induites par les camions
secoueurs permettant le développement de courbes du module de cisaillement in situ et de sa reduction sur une plage de grandes
déformations. L'effet de la composition des déchets a également été évaluée in situ.
KEYWORDS: in situ testing, shear modulus, nonlinear dynamic properties, municipal solid waste, landfills
1 INTRODUCTION
Assessment of the dynamic properties of Municipal Solid Waste
(MSW) is required for seismic response analyses of MSW
landfills in areas of moderate to high seismicity. Dynamic
properties in the linear range include shear wave velocity (
V
s
),
the associated small-strain shear modulus (
G
max
) and small-
strain material damping in shear (
λ
min
). The dynamic properties
in the nonlinear range include the (normalized) shear modulus
reduction and material damping increase curves. The total mass
density of MSW is also an important property in these analyses.
Historically, two approaches have been used to evaluate the
nonlinear dynamic properties of MSW: (1) analytical studies
that are based on back-calculation of the response of
instrumented landfills (e.g., Augello et al. 1998, Matasovic and
Kavazanjian 1998, Elgamal et al. 2004) and (2) large-scale
laboratory testing of MSW (e.g., Matasovic et al., 1998, Lee
2007, Zekkos et al. 2008, Yuan et al. 2011).
Field measurements of small-strain properties have been
restricted to direct measurements of
V
s
(e.g., Kavazanjian et al.
1996, Matasovic and Kavazanjian, 1998, Sahadewa et al. 2011)
and mass density (e.g., Matasovic and Kavazanjian, 1998,
Zekkos et al. 2006). This contribution outlines a MSW field
testing program that was implemented to directly assess the
shear modulus reduction curve of MSW.
2 METHODOLOGY
Field testing was performed at the Austin Community Landfill,
in Austin, Texas, U.S.A, following the basic methodology
proposed by Stokoe et al. (2006) and the field testing approach
proposed by Stokoe et al. (2011). The testing was performed at
two representative locations. Shear wave velocity profiling
using the Spectral Analysis of Surface Waves (SASW) method
was performed first at each location. Two vertical arrays of
three-component geophones were then embedded in the waste at
four different depths up to a maximum depth of about 1 m. The
depth of the sensors was varied at the two locations. A 0.91-m
diameter, 0.3-m thick, unreinforced, prefabricated concrete
foundation was placed on top of the sensors. Source rods for
crosshole seismic testing were placed at a distance of 1.14 m
from the first array as shown in Fig. 1. Downhole seismic
testing was also performed by striking the side (for shear, S) and
top (for compression, P) of the footing and recording arrivals of
S and P waves, respectiverly, at the geophone arrays. Then two
mobile vibroseis shakers, Thumper and T-Rex, shown in Fig.2,
owned and operated by the George E. Brown, Jr. Network for
Earthquake Engineering Simulation at University of Texas
(NEES@UT), were used to excite the footing. Thumper was
used for the low ground pressure tests and T-Rex was used for
higher ground pressure tests.
Proceedings of the 18
th
International Conference on Soil Mechanics and Geotechnical Engineering, Paris 2013
1
In Situ Assess t of the Nonlinear Shear Modulus of Municipal Solid Waste
Évaluation i it
le non linéaire de cisaillement des déchets solides municipaux
D. Zekkos, A. S hadewa & R. Woods
University of i i
r r
K. Stokoe, II
University of Texas, stin
N. Matasovic
Geosyntec Consultants
ABSTRACT: s
a ic properties of Municipal Solid Waste (MSW) is required for seismic response a alyses of
existing MS la fill
s f moderate to high seismicity. While material pro erties such as shear w ve velocity and unit weight
can be readily eas r , ssess ent of nonlinear dynamic properties of MSW has, to date, been restricted to specialty laboratory
testing of reconstituted
speci ens and back analysis of recorded earthquake response. Both approaches have limitations. In this
paper, the results of direct in-situ measurements of both small-strain shear modulus and the nonlinear shear modulus reduction
relationship are presented. The measurements were performed at a landfill in Austin, Texas, using two mobile vibroseis shakers. In
situ tests were performed at two locations. The vertical static load imposed by the vibroseis was varied to evaluate the effect of
vertical stress on the dynamic properties of the MSW. Dynamic testing was performed at increasing horizontal loads inducing small to
large strains in the MSW. Shear strains ranging from 0.0002% to 0.2% were induced by the shakers allowing the development of in
situ shear modulus reduction curves over a large strain range. The effect of waste composition was also assessed in situ.
RÉSUMÉ : L’Évaluation des propriétés dynamiques des déchets solides municipaux (MSW) est nécessaire pour les analyses de
réponse sismique des décharges de DSM existants dans les zones de sismicité odérée à élevée. Bien que les propriétés matérielles
telles que la vitesse des ondes de cisaillem nt et poids unitaire peut être facilement mesurée, l'évaluation des propriétés dynamiques
non linéaires d DSM a, à c jour, été limité à des test de laboratoire spéci lisés d spécimens reconstitués de DSM et de l'analyse
i verse de la réponse au tr mblement de terre enregistré. Les deux approches ont leurs limites. Dans cet article, les résultats des
m sures directes i situ de d ux modules de cisaillem nt a faibl contrainte et la relation non néaire de la reduction du module de
ci aillement sont présentés. Les es r ont été effectuées dans une décharge à Austin, au Texas, utilisant d ux gr s camions
secoueurs vibr sismiqu s. Les es ais in situ t été effectuées à deux endroits. L charge verticale statique imposée par les camions
secoueur a été odifiée afin d'évaluer l'effet de la contrainte verticale sur les propriétés dynamiques de la DSM. Des essais
dynamiques ont été réalisés tout en augmantant les charges horizontales qui ont cree des deformations variant entre des petites et des
grandes déformations dans le DSM. Des déformations de cisaillement allant de 0,0002% à 0,2% ont été induites par les camions
secoueurs permettant le développement de courbes du module de cisaillement in situ et de sa reduction sur une plage de grandes
déformations. L'effet de la composition des déchets a également été évaluée in situ.
KEYWORDS: in situ t sting, shear m dulu , nonlinear dyna ic properties, municipal solid waste, landfills
1 INTRODUCTION
Assessment of the dynamic properties of Municipal Solid Waste
(MSW) is required for seismic response analyses of MSW
landfills in areas of moderate to high seism ty. Dynamic
propertie in the linear ange in lud shear w ve velocity (
V
s
),
the as ociated mall-strain sh ar modulu (
G
max
) and small-
strain material damping in shear (
λ
min
). The dynamic pr perties
in the nonlinear range include the (n rmalized) shear modulus
reduction and material damping increase curves. The total mass
density of MSW is also an important property in these analyses.
Historically, two approaches have been used to evaluate the
nonlinear dynamic properties of MSW: (1) analytical studies
that are based on back-calculation of the response of
instrumented landfills (e.g., Augello et al. 1998, Matasovic and
Kavazanjian 1998, Elgamal et al. 2004) and (2) large-scale
laboratory testing of MSW (e.g., Matasovic et al., 1998, Lee
2007, Zekkos et al. 2008, Yuan et al. 2011).
Field measurements of small-strain properties have been
restricted to direct measurements of
V
s
(e.g., Kavazanjian et al.
1996, Matasovic and Kavazanjian, 1998, Sahadewa et al. 2011)
and mass density (e.g., Matasovic
d Kavazanjian, 1998,
Zekkos et al. 2006). This contribution outlines a MSW fi ld
testing program that was implemented to directly assess the
shear modulus reduction curve of MSW.
2 METHODOLOGY
Field testing was performed at the Austin Community Landfill,
in Austin, Texas, U.S.A, following the basic ethodology
proposed by Stokoe et al. (2006) and the field testing approach
pro sed by Stokoe et al. (2011). The testing was performed at
two representative l cations Shear wave velocity profiling
using the Sp ctral Analysis of Surface Waves (SASW) method
was performed first at each location. Two vertical arrays of
three-component geophones were then embedded in the waste at
four different depths up to a maximum depth of about 1 m. The
depth of the sensors was varied at the two locations. A 0.91-m
diameter, 0.3-m thick, unreinforced, prefabricated concrete
foundation was placed on top of the sensors. Source rods for
crosshole seismic testing were placed at a distance of 1.14 m
from the first array as shown in Fig. 1. Downhole seismic
testing was also performed by striking the side (for shear, S) and
top (for compression, P) of the footing and recording arrivals of
S and P waves, respectiverly, at the geophone arrays. Then two
mobile vibroseis shakers, Thumper and T-Rex, shown i Fig.2,
owned and operated by the George E. Brown, Jr. Network for
Earthquake Engineering Simulation at University of Texas
(NEES@UT), were used to excite the footing. Thumper was
