38
Geotechnical News December 2011
WASTE GEOTECHNICS
impact monitoring, and the need for
long-term post-closure care (≥30
years).
The research program proposed the
development of sustainable landfill
technology through manipulating the
biochemical process of MSW landfills
and reducing the intensity and duration
of the hazards by taking more active
measures, particularly during the oper-
ation stage. Based on previous research
findings, the biochemical process can
be controlled by controlling the biore-
actor environment through the design
of gas and leachate circulation systems.
The new design functions of the circu-
lation systems would include leachate
recirculation, control of the oxidation-
reduction environment, control of pH
circumstance, three-dimensional drain-
age of gas and leachate, etc. It is an-
ticipated that such active measures will
significantly reduce the amount of time
needed for landfill stabilization, mass
loading of contaminants and post-
closure settlement as well as properly
control gas and liquid pressures. Ex-
perimental data indicates that the sta-
bilization time of Chinese MSW can be
reduced by 50%, and the mass loading
of organic contaminants in leachate can
be reduced by 60%. With a significant
reduction in the loading and duration of
contaminants, the landfill barriers will
be able to serve for the entire life of the
MSW landfill.
Key Scientific Problems,
Research Topics and Targets
The development of the above-
mentioned
sustainable
landfill
technology
requires
a
deep
understanding on the following key
scientific problems (see Figure 4):
(1)
Bio-physico-chemical processes
of MSW and solid-liquid-gas interac-
tion in a landfill:
The bio-physico-
chemical process of MSW within a
landfill is very complex and interac-
tive, involving the bio-degradation of
organics, generation of gas, leachate,
heat and contaminants, changing of
oxidation-reduction and pH environ-
ment, compression of the solid skel-
eton, conduction of gas, liquid and
heat, etc. The bio-physico-chemical
process and associated solid-liquid-gas
interaction need to be evaluated at the
full scale of the landfill. Such interac-
tion results in significant engineering
effects including changes in material
properties, build-up of gas and liquid
pressures, deformation of the landfill
and mass loading of contaminants. The
study of this problem will contribute
to our understanding of the generation
and evolution of hazardous sources and
to developing a method for optimizing
the bio-physico-chemical process.
(2)
Landfill flowslide mechanisms
induced by gas and liquid pressures:
MSW landfills have a heterogeneous
structure with a wide range of materi-
als. Daily and temporary soil covers
usually result in a less permeable lay-
er. Less permeable layers or perched
leachate mounds may trap the abun-
dant landfill gas, and a build-up of gas
pressure will form. The gas and leach-
ate interact with each other and exhibit
a coupled effect. The landfill flowslide
mechanisms induced by the coupled
effect of gas and liquid is not under-
stood and will be investigated in this
program.
(3)
Breakthrough process of leach-
ate, gas and contaminants in barriers:
Landfill barriers include the top cover
system and the bottom liner system.
The top cover suffers from seasonal
cycles of wetting/drying and freezing/
thaw, dramatic climatic change and dif-
ferential settlement. The bottom liner
suffers from large surcharge loading,
high liquid pressure, high temperature
and large contaminant loading. From
a physical view, both kinds of barri-
ers are subjected to multi-field coupled
loading. The long-term performance
of the barriers under complex load-
ing conditions is not fully understood.
The breakthrough process of leachate,
gas and contaminants in barriers under
multi-field coupled loading conditions
will be studied in this program.
The research topics identified in this
program are as follows (see Figure 5):
(1) bio-physico-chemical processes of
MSW and generation of contaminants;
(2) solid-liquid-gas interaction in land-
fills and active control methods; (3)
landfill flowslide mechanisms induced
by gas and liquid pressures and risk as-
sessment methods; (4) breakthrough
process of leachate and contaminants
in bottom barrier and control methods;
(5) breakthrough process of gas and
water in final earthen cover and control
methods; and (6) assessment of landfill
performance and sustainable landfill
technology. Topics 1 and 2 will be in-
vestigated on the element and landfill
scale, respectively, and the research
will characterize hazardous sources for
the other topics. The active control or
method of tuning for an optimum bio-
physico-chemical process (Topic 2),
the tuning method for liquid and gas
pressures (Topic 3) and the lifecycle-
based barriers (Topics 4 and 5) will be
Figure 3. Blowout of a gas-leachate
mixture to a height of 5 m from a bore-
hole drilled at a landfill.
Figure 4. Key scientific problems of the
research program
Figure 5. Program research topics
