Shear strength and creep settlement properties of municipal
solid waste at the Chong Qing Landfill, China
5 (Department of Civil Engineering, ChongQing University, ChongQing 400045)
Abstract: This paper presents experimental results on geotechnical properties of municipal solid waste
(MSW) at different biodegradation phases. The shear strength of fresh and landfilled municipal solid
waste was determined by large direct shear tests (LDS). For fresh samples, the cohesion was increased
from 0kPa to 19.89kPa, and the friction angle decreased from 27.84?to 14.41? as biodegradation 10 degree increased from 0 to 63.83%.. For the triaxial tests under the consolidation drained (CD)
condition, the shear strength of cohesion and friction angle for degraded samples presents a continuous
increasing when the defined axial strain is increased from 5% to 20%, and the cohesion is vary from
35.90kPa to 66.42kPa, the drained friction angle ranged from 29? to37?. A narrow range for organic
content and temperature that better for biodegradation and creep settlement were found in the creep 15 tests, and it was ranged from 21.9% to 36.47%, 22? to 41?, respectively. The test results are useful for
assessing the stability and creep settlement of landfills located in ChongQing city, in China.
Keywords: Municipal solid waste; Shear strength; Biodegradation; Creep settlement; Leachate
20 Increasingly affluent life styles and population, continuing industrial and commercial grow in
und the world over the past decade has been accompanied by rapid increases in many countries aro
both municipal and industrial solid waste production. As the economical disposal way of MSW,
52%,90%,95%,54.3%and 83%of urban wastes production are landfilled into regulated centers,
respectively, in Korea, Poland , Taiwan, USA, and China. (L.Di Palma et al., 2002;US EPA,2009?
25 Tony L.T.Zhan,2008). However, with the continuous increasing of height and volume in the
landfills, significant landfill slides have been triggered. For example, the largest Maine Slop
failure in the United states happened in the 1996, march 9(Eid et al.,2000); and The Payatas
landfill slide in Quezon City, Philippines, it was triggered by the extremely heavy rains from two
typhoons, and at least 278 people were killed in this disasters(Merry.S.M,et al., 2005). 30 Consequently, assessing the stability of landfill is becoming one of the major concerns for
engineering designers. And the Shear strength is required as the primary factors for calculation.
Numerous studies has been conducted on it at field and laboratory tests.~Edil et al.,1990?Landva
and Clark, 1990?Howland and Landva,1992?Jessberger and Kockel, 1993?Wall, D.K.&
Zeiss,1995?Grisolia et al.,1995?Houston et al.,1995?Kavazanjian et al.,1995?Kockel and
35 Jessberger,1995?Edincliler et al.,1996?Van Impe,1998? Thomas et al.,1999? Pelkey et al.,
2001? Caicedo et al.,2002?Vilar and Carvalho, 2004?Gomes et al., 2005?Itoh et al., 2005?
Feng, 2005?O.M.Vliar, 2005?T.L.T.Zhan et al.,2008; Dixon et al., 2008? Reddy,2008?
Reddy,2009a?Reddy, 2009b?Reddy, 2011??.It is believed that the degradation of organic matter
in the waste could resulted in the changes of the particle sizes and composition of MSW, and the 40 shear strength properties and moisture content in the waste could be also changed (Reedy et
al.,2011).However, shear strength values reported in previous literatures varied widely (the
cohesion varied from 0.5kPa to 71kPa, and inter friction angle ranged from 17.8? to 34?), and little
studies focused on determining the change in properties of MSW due to the biodegradation under
aerobic and anaerobic condition, therefore, further studies are needed to better understand the
45 effect of decomposition on the shear strength. However, it is difficult to identify the shear strength
Brief author introduction: Zhao Yanri, ph.d. E-mail: email@example.com
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properties because of its heterogeneous nature and biodegradation degree, and it has been
becoming one more important thing for engineering designers to evaluate the stability of landfill
by using the suitable shear strength value of MSW at different biodegradation levels.
Information on the creep settlement is also required to evaluate the total settlement and 50 stability in the landfill, Numerous researches have been studied on it (Sowers,1973?Yen and
Scanlon,1975?Tan et al., 1991?Rao and Oweis, 1977? Gabr et al., 2000?Hossain and Gabr.,
2005?Hettiarachchi et al., 2003,2005,2009?Marques, 2001,2003?Elagroudy, 2008?Bareither,2008;
Machado, 2002, 2008?Sivakumar and Babu, 2009?).An additional factor is the change of
proportion of creep settlement in the total settlement due to the organic degradation. Coduto and 55 Huitric.(1990) pointed out that the secondary compression settlement can be enlarged by the creep
settlement due to the biodegradation. Pump.(1998), M.S wati and Kurian Joseph.(2008) indicated
that the secondary settlement caused by the natural biodegradation reached to 40% ,and even
reached to 49% of total settlement by using the recirculation of leachate. However, little research
has been conducted on investigation the effect of biodegradation and temperature on the creep 60 settlement due to the biodegradation in the landfill.
This paper describes a comprehensive laboratory study on Chong Qing landfill in China. The
borehole samples collected at the different depth are shredded at the laboratory before the tests,
and the shear strength properties of MSW samples were estimated using a series of larger direct
shear tests (LDS) at the different biodegradation phases. The effect of organic content on shear 65 strength of MSW due to the biodegradation was also identified in this study. Through the three
axial shear test under consolidation drained (CD) condition, the correlation between shear strength
of landfilled sample with the different shear strain of axial (5%, 10%, 15%, 20%) were clarified,
and the effect of temperature on the degradation was clarified too. Unless stated otherwise, creep
settlement tests were performed under the no precipitation condition during tests, and all of the 70 experiments were carried out in accordance with the standard procedures established by the China
Society of standard for soil test method (GB-T/50123-CSTM 1999).
1 Sample collection and characterization
Fresh and landfilled sample were prepared, which collected from the shallow of 1-3 meters
layers and the depth of 25m, respectively, in Chong Qing landfill. Composition of the MSW was 75 determined and grouped into different friction (organic friction, inorganic friction, cinder and
During the shear tests, The fresh and landfilled of shredded samples were prepared and all the
samples were shredded before the drained direct shear tests. The shredded sample was dried and
gradation was determined using sieves (size of sieves: 100,50,20,10,5mm) analysis in accordance 80 with (GB-T/50123-CSTM 1999), the typical gradation of MSW was shown in fig 1. It is observed
that approximately 95.3% particle sizes of shredded MSW are less than 10 mm.
In order to investigate the effect of degradation on the shear strength of fresh MSW, and 45
fresh shredded samples (organic content is 45.95 %) and 28 shredded partially degradable samples
were prepared for the lager direct shear test.
85 Table 1* Typical components of MSW of research areas Category Organic Inorganic (I) Other Cooking andWooBrickTextile Plasti type Waste type Bones PaperMetalGlass Cinder s c Garden wa ste d and tile 2.19 17.21 30.48 Percent(%) 22.82 1.55 5.39 2.84 11.82 1.53 1.16 3.01 3.57 30.48 Total (%) 45.95 2
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Table 2* Range and representative value of MSW‘s natural water content Cooking andBrickWaste type Textiles Plastic Wood MetalGlass CinderBones Paper Garden and tile wa ste
Percent(%) 50~80 5~20 4 ~10 6~15 1~4 15~40 2~4 6~12 1~4 6~12 Typical Percent670 15 6 10 2 20 3 8 2 ~%? *Table 1 and 2 dates were afforded by eco-environment science research institutes of Chong Qing. 90
The effect of moisture content on the shear strength of the landfilled MSW(older than 10 years) was conducted through the Drained Large direct shear test (DLDS).In order to avoid the particle sizes effect, landfilled samples were shredded and reconstructed at different moisture contents.
the borehole samples were initially subjected to a confining pressure of During the LDS tests, 95
40kPa and a vertical pressure of 30kPa and rest for 24 h before the tests. Latterly, the shearing was done at a low constant strain rate (0.1mm /min) under different normal stress conditions (50, 100,
200, 300, 400kPa). The shear strength was defined at 15% horizontal deformation and was used to establish the Mohr-coulomb shear envelopes. The tests stopped when the horizontal placement
exceeds 6mm. The LDS tests were repeated for the other shredded landfilled samples.100 100 90 80 70 60 50