Nature and Phase Properties of Unsaturated Soil - Unsaturated Soil Mechanics in Engineering Practice - page 76

2.23

2.13

2.03

1.93

1.83

1.73

1.63

Model prediction—static (2100 kPa)
Model prediction—dynamic (4000 kPa)
Experimental data—static (2100 kPa)
Experimental data—dynamic (3000 kJ/m 3 )

1.53

1.43

6 8 10 12 14 16 18

Water content, %

Figure 2.51 Comparison of the predicted and experimental compaction curves for clayey sand
soil (data from Kenai et al., 2006).

total stress, m 1 . Further research is necessary in order to
better understand all factors influencing compaction curves.

2. There is a combining (or coupling) of more than
one process. In geotechnical engineering, the term
“coupled” is reserved for situations where more than
one type of partial differential equation is solved

simultaneously.
3. The processes involved may be thermally driven, par-
ticularly in the case of MSW.
4. The principles and theories of unsaturated soil mechan-
ics must be incorporated into the formulation of the
partial differential equations that describe the physi-
cal processes. In other words, the materials involved
in both situations are commonly subjected to varying
degrees of saturation as the processes proceed.
5. The partial differential equations being solved are
nonlinear in form, meaning that special “numerical
solvers”

2.6 VOLUME-MASS RELATIONS WHEN MASS IS
LOST FROM SYSTEM

A special class of geotechnical engineering problems exists
where mass is lost from the system while one or more pro-
cesses are taking place. One such situation involves heap
leach processes. Another example involves the processes
associated with the management of municipal solid waste
(MSW). While these two examples may appear to be quite
different, there are a number of features that are similar to
both processes. Both problems have features that are not
commonly addressed in classical soil mechanics.
Some material properties involved in problems involv-
ing the loss of mass are different than those commonly
encountered in geotechnical engineering. However, it is the
change in solids content with time that makes these prob-
lems unique from most other modeling simulations common
to geotechnical engineering practice. Certain material prop-
erties change with time when the solids content changes
with time. There are independent processes associated with
the loss of material that must be taken into consideration
when formulating the mathematical equations to be solved.

will likely be needed to ensure that the

solutions converge to the “correct” answer.
6. Consideration of air flow and heat flow may be relevant
to both situations with air flow playing a key role in
the MSW problem.
7. Modeling may be of the transient form, which means
that starting conditions (or initial conditions) must be
determined or assumed.
8. There are significant geoenvironmental issues that need
to be addressed for both the MSW and heap leach
problems.

2.6.1 Similarities between Heap Leach and Municipal
Solid Waste Problems
Let us consider some similarities between heap leach prob-
lems and municipal solid waste problems:

2.6.2 Differences between Heap Leach and Municipal
Solid Waste Problems
The differences between heap leach problems and municipal
solid waste problems are as follows:
1. The generation of gas (predominantly methane) is a
dominant and significant process associated with pro-
cesses involved with MSW.

1. There is a loss of mass from the system with time in
both situations. This is a new feature that must be taken
into consideration.