3073
A New Approach for Characterizing Shear Strength of Municipal Solid Waste
for Land Fill Design
Une nouvelle approche pour la caractérisation de la résistance au cisaillement des déchets urbains
pour la conception des décharges
Singh S.
Santa Clara University
ABSTRACT: Many researchers have characterized shear strength properties of municipal solid waste (MSW) by proposing Mohr-
Coulomb strength envelopes derived from their experimental data. Still others reported results in terms of the same parameters after
obtaining the data from back-calculations of failed landfills. A factor which has not been paid much attention to is the highly
compressible nature of MSW. Variability in the unit weights, due to high compressibility of MSW, observed in the samples tested at
increasing confining pressures invalidate the use of a common Mohr-Coulomb envelope for these samples. This paper critically
examines the impact of the high compressibility of MSW on the development of Mohr-Coulomb strength parameters. It is argued that
a single Mohr-Coulomb envelope does not account for the high compressibility of MSW. A new approach based upon the use of
‘Strength versus Depth’ plot has been proposed.
RÉSUMÉ : De nombreux chercheurs ont caractérisé les propriétés de résistance au cisaillement des déchets urbains (MSW) en
proposant des enveloppes de résistance de type Mohr-Coulomb issues de leurs données expérimentales. D'autres encore ont présenté
des valeurs obtenues par analyse inverse de ces mêmes paramètres, à partir de cas de glissements observés dans des décharges. Un
facteur auquel n'a pas été accordé beaucoup d'attention est la nature hautement compressible des déchets. La variabilité massique, du
fait de la forte compressibilité des déchets, qui est observée dans les échantillons soumis à une pression de confinement croissante
invalide l'utilisation d'une enveloppe de Mohr-Coulomb pour ces échantillons. Cet article examine de manière critique l'impact de la
forte compressibilité des déchets sur le développement des paramètres de résistance de Mohr-Coulomb. Une enveloppe unique de
Mohr-Coulomb ne permet pas de tenir compte de la forte compressibilité des déchets. Une nouvelle approche basée sur la dépendance
de la résistance avec la profondeur est proposée.
KEYWORDS: Municipal Solid Waste, Shear Strength, Mohr-Coulomb concept.
1 INTRODUCTION
Every day, the United States alone generates millions of tons of
municipal waste solid waste (MSW) that must be processed.
Landfilling is the least expensive method of waste disposal and
landfills are being built to unprecedented heights. Landfill
failures can expose the public to a variety of health hazards and
can also create ecological and environmental disasters. These
and other reasons make the determination of design parameters
for landfills a growing field of interest. Geotechnical parameters
are important for the design of each of the subsystems such as
waste mass slope and height and the containment systems.. The
parameter of shear strength is important for both seismic and
static slope stability. Over the past decade, there have been
several publishing’s on shear strength of MSW as it pertains to
seismic and static slope stability. The data presented in these
publishings, however, reflects the variability of MSW in regards
to constituents and location. . Many question the applicability of
Mohr Coulomb concept with MSW and the effect of age and
compressibility on the evaluation of its strength parameters still
remains unanswered. Nearly vertical slopes in the MSW
landfills observed all over the world cannot be explained by the
frictional strength envelopes derived using Mohr-Coulomb
Approach. Accordingly, no clear cut way for characterizing the
shear strength of MSW has emerged. This paper attempts to
progress in this direction.
2 ALTERNATIVES FOR CHARACTERIZING STRENGTH
OF MUNICPAL SOLID WASTE
In the slope stability analysis of Municipal Solid Waste (MSW)
landfills, shear strength properties of the MSW are of high
importance. There have been different approaches to
characterize the shear strength properties of MSW. Fassett, et al.
(1994) presented a summary and analyses of MSW strength
properties and brought into focus the limitation of existing
approaches used to characterize shear strength properties of
MSW. Characterization has essentially been attempted in two
ways. Singh and Murphy (1990) summarized existing data
from laboratory test back-calculations and from in-situ testing
and recommended a range of strength parameters for MSW;
cohesion (
c)
and internal friction angle (Φ). Howland and
Landva (1992) used an alternate method and expressed MSW
strength in terms of mobilized shear strength (τ
m
) and normal
stress (σ
n
). Howland and Landva considered the strength of
MSW to be primarily frictional in nature. In terms of Mohr-
Coulomb parameters, the relationship between shear strength
and normal stress developed by Howland and Landva gave a
c
equal to 10 kPa and Φ equal to 23 degrees as a lower bound to
their data. Howard and Landva summarized MSW strength data
reported in the literature on four cases (New Jersey Landfill
Failure, California Landfill Load Test, Laboratory Direct-Shear
Tests and Field Direct Shear Tests). The data (figure 3 of their
paper) was plotted as mobilized shear strength and average
normal stress. Only the lower bound values were reported. No
upper bound values were estimated or reported. Kavazanjian, et
al. (1995) used an approach similar to that of Howland and
Landva, however, Kavazanjian relied more on back
