3008
Proceedings of the 18
th
International Conference on Soil Mechanics and Geotechnical Engineering, Paris 2013
Regarding the back-analysis of failures, the uncertainties
commented above limit their use.
One of the first proposals was due to Singh and Murphy
(1990), but with no attempt to reduce the wide ranges of
cohesion and friction resulting from real failures.
Based on the limited data available at the time, Sánchez et
al. (1993) proposed a joint consideration of the results of
laboratory and in situ tests and back-analysis of failures. The
first ones gave a set of pairs of values of cohesion and friction,
increasing with the strain. The real failure cases help to identify
the relevant strain level, and reciprocally, the lab tests help to
identify the real c/
ratio. In situ tests can also give information
on that respect. The result is shown in Figure 5.
0
20
40
60
80
100
0
10
20
30
40
50
60
Back analyses (by 1990)
Lab tests (by 1990)
Sánchez et al. (1993)
Friction angle,
(
o
)
Cohesion, c (kPa)
Figure 5. Strength parameters. Early design recommendations (Sánchez
el al., 1993)
In the last two decades, some additional results have been
published, from laboratory and in situ tests and from real
failures (see, for instance, the compilation by Stark et al. (2009),
among others). Considering these data, the recommended values
in Figure 5 can be increased. Figure 6 includes the results of
failures compiled by Stark et al. (2009), and their recommended
values, based on the proposal by Eid et al. (2000).
0
20
40
60
80
100
0
10
20
30
40
50
60
Back analyses (by 2009)
Strain levels (Stark et al., 2009)
Stark et al. (2009)
Possible new proposal
5%
10%
20%
Friction angle,
(
o
)
Cohesion, c (kPa)
Figure 6. Additional data. Modifications to Figure 5.
5 CONCLUSIONS
Prior work has shown that it is no easy to obtain the mechanical
properties of the waste mass.
After merging the data from the revision of existing
bibliography and the experience of the U.C. Geotechnical
Group, new research is being undertaken in order to establish a
method to perform that task during the next three years. The
study will be based on the use of field tests, complemented with
medium to large scale laboratory direct shear tests. It will cover
several landfills, with conventional MSW, together with wastes
subjected to mechanical and biological pre-treatment (MBT),
introduced in Spain in the last years (projects GEORES-
03.2843.64001 and PROMERSU-BIA2012-34956).
The study will be performed in several landfills. In parallel
with the test campaign, numerical modelling of the landfills
under study will be undertaken to obtain feedback and refine the
data acquisition process.
After all the data are gathered and the process is considered
optimum, a method to obtain the mechanical properties of a
landfill using field tests and a new proposal for the design
strength parameters will be obtained as a result of the research.
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