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th
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Proceedings of the 18
th
International Conference on Soil Mechanics and Geotechnical Engineering, Paris 2013
4
The entire dataset from location #1 is shown in Fig. 9, and
exhibits more variability than shown earlier because it includes
variations of both waste composition and, to a lesser effect,
confining stress. Shear modulus was evaluated for shearing
strains ranging from 0.0002% up to 0.2%. Datasets from
locations #1 and #2 are shown in Fig. 10 with open black
squares and open red circles, respectively. The normalized shear
modulus reduction curves are generally consistent, although
shear modulus reduction appears to be more pronounced at
larger strains for location #2 compared to location #1, which is
likely attributed to variability in waste composition.
The field experiment data can be compared to the Zekkos et
al. (2008) laboratory-based recommended curves at low
confining stresses for variable waste composition. The field data
are generally consistent with the laboratory based curves, shown
as lines in Fig. 10. Field data for location #1 are consistent with
the Zekkos et al. (2008) curves for waste-rich MSW specimens.
The
G
/
G
max
data from location #2 are generally consistent with
these curves for strains up to 0.05%, but at larger strains shear
modulus appears to drop off more sharply than recommended
by Zekkos et al. (2008).
Figure 9.
G
/
G
max
- log
γ
relationships in location #1.
Figure 10.
G
/
G
max
- log
γ
relationships estimated at locations #1 & #2.
5 CONCLUSIONS
In situ data on shear modulus and the normalized shear modulus
reduction as a function of shear strain have been generated at a
Municipal Solid Waste landfill in Austin, Texas using mobile
vibroseis shakers that are operated and maintained by
NEES@UT. The methodology described in this paper can be
used to evaluate nonlinear properties of MSW in situ over a
wide shear strain range (0.0002% to 0.2%).
The impact of waste variability and confining stress on the
shear modulus was also assessed in situ. Shear modulus was
found to increase with increasing confining stress and to be
substantially affected by waste composition. The normalized
shear modulus reduction curves were also affected by waste
composition and, to a lesser extent, confining stress. The
normalized shear modulus also becomes systematically more
linear as confining stress increased, similarly to soils.
6 ACKNOWLEDGEMENTS
This paper is based upon research supported by the National
Science Foundation, Division of Civil and Mechanical Systems
under Grant No. CMMI-1041566. Any opinions, findings,
conclusions and recommendations expressed in this paper are
those of the authors and do not necessarily reflect the views of
the National Science Foundation. Additional information about
this research project is available on the research project’s
website on GeoWorld
.
The authors would like to thank Dr. Farn-Yuh Menq, Cecil
G. Hoffpauir, and Robert Kent of the NSF-funded
NEES@UTexas Equipment Site for their contribution with field
testing. We would also like to thank Mr. Jason Lang of Waste
Management of Texas, Inc. for his logistical support, and Ms.
Lindsay O’Leary of Geosyntec Consultants for her contribution
with in-situ measurement of the MSW unit weight.
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10
-4
10
-3
10
-2
10
-1
1
0.0
0.2
0.4
0.6
0.8
1.0
Element A (depth ~ 0.32 m;
14 - 89 kPa)
Element B (depth ~ 0.43 m;
13 - 69 kPa)
Element C (depth ~ 0.60 m;
11 - 47 kPa)
Element D (depth ~ 0.61 m;
11 - 46 kPa)
Element E (depth ~ 0.77 m;
11 - 35 kPa)
Element F (depth ~ 0.89 m;
11 - 30 kPa)
G/G
max
Shearing Strain (%)
Location #1
~ 11 - 89 kPa
10
-4
10
-3
10
-2
10
-1
1
0.0
0.2
0.4
0.6
0.8
1.0
ACL (this study)
Location #1 (
0
~ 11 - 89 kPa)
Location #2 (
0
~ 11 - 106 kPa)
Zekkos et al. 2008 (
0
< 125 kPa)
100% material < 20 mm
62-76% material < 20 mm
8-25% material < 20 mm
A
G
/
G
max
Shearing Strain (%)
