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2012. Vol.3, Supplement, 148-153
Published Online December 2012 in SciRes (http://www.SciRP.org/journal/ce) DOI:10.4236/ce.2012.37B039
Copyright © 2012 SciRes.
Beneficial Experience from Teaching and Education to
Research and Development
Department of Construction Engineering, École de technologie supérieure, Université du Québec, Montréal,
Teaching and Education (T&E) constitute the most important activity in knowledge transfer from genera-
tion to generation. This can explain why government organizations consider the training of highly quali-
fied personnel as one of the most important criteria in the selection of research and development (R&D)
grant applications. A university professor should thus not only play the role of researcher, but also that of
teacher. T&E and R&D combine to form an inseparable relationship for university professors. By shoot-
ing for excellence in T&E, we could get a new perception of a familiar field or initiate a brand new field
altogether, which would in turn enhance our research. The quest for excellence in R&D leads to deeper
and better understanding of materials taught, and progress in R&D enriches our T&E endeavors. Here, the
author shares a beneficial experience from T&E to R&D.
Keywords: Teaching and Education (T&E); Research and Development (R&D); Soil Mechanics;
Laboratory Tests; Excess Pore Water Pressure; Self-weight Consolidation
As a parent and a teacher, the author considers education to
be extremely important. Obviously, when we talk about “edu-
cation”, we usually mean the “teaching”. Considerable impor-
tance should definitely be attributed to teaching and education
(T&E) as they provide the only means of transferring social and
scientific knowledge from generation to generation, and to
ensure continuity in human culture and civilization. This can
explain why the NSERC (Natural Sciences and Engineering
Research Council of Canada) considers the training of highly
qualified personnel (HQP) as one of the three most important
criteria for research and development (R&D) funding allocation
under the Individual Discovery Grant Program .
On the other hand, a university professor also plays the role
of researcher who has the mission to perform research to ad-
vance human knowledge.
Thus, a university professor has an obligation to strive for
excellence both in T&E and R&D. In fact, the relationship be-
tween T&E and R&D is inseparable for a university professor.
There is a Chinese expression that states that “Revision of old
knowledge might lead to new perception” . By striving for
excellence in T&E, we might initiate a brand new, as yet unfa-
miliar R&D field, or obtain some new ideas in a familiar field,
which will enhance our R&D. T&E may thus be considered as
a resource feeding our R&D.
On the other hand, striving for excellence in R&D could pro-
vide a better and deeper understanding of our materials taught.
This may increase our confidence level in our teaching and
facilitate the assimilation of new knowledge by students. Fur-
thermore, R&D often enriches our T&E material.
Here, the author shares a beneficial experience from T&E to
T&E of Soil Mechanics
As a professor in geotechnics, the author teaches the “Soil
Mechanics” course. In most geotechnical works, it is well es-
tablished that this is a difficult course, which however includes
some basic components, constituting the most important ones
for further geotechnical applications. The most difficult parts of
the course include the calculation of total and effective stresses
and a distinction between long-term and short-term shear
strengths, among other things. The latter is closely related to the
generation and dissipation of excess pore water pressure in fin
In the textbook used for the author’s “Soil Mechanics”
course, a newly deposited backfill is taken as an example of
under-consolidated soil with an over-consolidation ratio (OCR)
smaller than unity . In the author’s opinion, the newly depo-
sited backfill is not an under-consolidated soil. Instead, it is a
good example of the confusion that exists between total stress
and effective stress. To illustrate this, one considers a newly
deposited backfill in liquid (mud) form shown in Figure 1.
The relationship between the vertical total (
v) and effective
'v) stresses is expresse d as follows:
where uw is the pore water pressure. The vertical total stress at a
depth, h, can be calcualted by the following equation:
tot is the total unit weight of the saturated deposition. At
time 0 (starting) since the deposition, the backfill is in liquid
state, and no particulate-to-particlurate contact exists as yet.
Thus, the effective stress is zero, i.e.,
Copyright © 2012 SciRes.
A newly deposited backfill.
Entering Eqs. (2) and (3) into Eq. (1), we obtain the pore
water pressure at a depth, h, as follows:
tot is usually higher than the unit weight of water,
(4) indicates that the pore water pressure at a depth, h, is higher
than the hydrostatic pressure of water (=
wh). Theoretically , if
a piezometer is installed at the depth, h, a water height, hw,
would be expected in the piezometer as follows:
This equation indicates that the water column in the piezom-
ter, hw, should be higher than the water table, h as
tot is usually
w. The water column above the water table is
called the “excess pore water perssure height”, which can read-
ily be detected by an electronic piezometer.
However, if a conventional tube piezometer was installed,
nothing would probably be found in the piezometer. The reason
for that will be given below. This may however lead to a false
conclusion that the pore water pressure is nil and that the verti-
cal total stress,
v, is the same as the vertical effective stress,
After a period of drainage and consolidation, the true vertical
effective stress is increased to
'v0, which is the maximum ver-
tical effective stress to which the newly deposited backfill has
been submitted during its past history. Thus, its pre-consoldia-
'p, would be:
Obviously, the over-consolidatio ratio of the newly deposited
This means that the newly deposited backfill is always a
normally consoldiated soil.
However, if we were to take the vertical total stress
which can be directely calculated from Eq. (2), as the the verti-
cal effective stress,
'v0, we would obtain an OCR smaller than
one1, as follows:
False calculationTrue state
To confirm these hypotheses, and especially, to obtain a
visualization of the excess pore water pressure, a laboratory
instrumentation was built. This was part of the tasks realized by
the author during the 2011-2012 school year to improve his
T&E quality. The materials presented here has been used in the
author’s teaching to faciliate comprehension of the very ab-
stract “excess pore water pressure” concept by students.
Laboratory Tests for T&E
Newly Deposited Backfill Material
The material of a newly deposited backfill was made from
waste clayey samples, which had been used and stored in a
bucket over several terms of the “Soil Mechanics” course in the
École de technologie supérieure (ÉTS) Department of Con-
struction Engineering. All these dry clayey samples were first
well mixed, ground, and brewed with sufficient water to obtain
an over saturated clayey liquid-like sample (Fi gure 2).
Instrumentation and Tests
Figure 3 shows the instrumentation used to investigate the
self-weight consolidation behaviour of a newly deposited back-
fill. Sand is put in the bottom of a rigid wall cylinder, and cov-
ered with geotextile and filter paper. A piezometer is introduced
into the sand layer.
Figure 4 shows the situation in the beginning (Figure 4(a))
and the near end (Figure 4(b)) of the backfill deposition.
Visualization of Excess Pore Water Pressure
The term “excess pore wate pressure” has been defined pre-
viously, and is closely related to the long-term and short-term
stability of earth workings. Because the textbook  does not
provide for its visualization, it is too abstract to understand for
Material of a newly deposited backfill sample.
Same false conclusion can also be deduced if the hydrostatic pressure is
taken as the pore water pressure as the former is smaller than the latter.
Copyright © 2012 SciRes.
Self-weight consolidation instrumentaion.
Deposition of a backfill at the b eginning (a) and near the end (b) into a
rigid wall cylinder instrumented with piezometer.
Figure 5 shows the water column in two piezometers: one
inserted into the lower sand layer, and the other directly intro-
duced into the upper clayey backfill. A water column higher
than the water table is observed immediately after the end of
the backfill deposition, but no water is observed in the upper
piezometer (Figure 5(a)).
After about two days of drainage and consolidation, the wa-
ter column in the lower piezometer becomes lower while some
water begins to be observed in the upper piezometer, whose
head is much lower than the water table in the cylinder (Figure
5(b)). This is due to the fact that the clayey backfill has a very
low permeability compared to sand. Thus, the lower piezometer
can be fed with water immediately as long as it is requested by
the pore water pressure, while little water is avaiable from the
clayey backfill to feed the upper piezometer. The latter corre-
sponds to the case when a tube piezometer is installed in a
newly deposited low permeability backfill.
Visualization of Drainage Flow
With the standard consolidation (oedometer) test , it is
usually difficult to see water flow, given the limitations in sam-
ple size and availability of expulsed water from the consoli-
dated sample. In fact, water outflow is usually smaller than the
evaporation, and as a result, water must be added to ensure the
sample saturation during standard consolidation tests.
With the instrumentation presented here, one-dimensional
upward drainage is allowed even though a pervious sand is
placed at the base of the deposition.
Figure 6 shows a picture in which a 5.2 cm water decanta-
tion is clearly formed after about 260 hours of self-weight con-
solidation. Doubtless, this material can be used in teaching the
“Soil Mechanics” course in order to facilitate comprehension of
drainage and consolidation.
Piezometer readings: (a) immediately after the backfill deposition; (b)
after about two days of self-consolidation.
Water decantation after 260 hours and 33 minutes of self-weight
Copyright © 2012 SciRes.
R&D Benefits fro m T&E
Improvement in Instrumentation
The pictures shown in Figures 2 to 5 were taken during the
primary tests. Figure 7 shows an instrumentation after several
improvements, including a better sealing system, the placement
of a sand layer only slighly higher than the piezometer needle
position, and the attachment of the piezometer to avoid or re-
duce human disturbance to the water head during testing. The
pictur presents the designations of several measured parameters,
including the total height of the backfill deposition (Ht), the
thickness of the sedimentation due to self-weight consolidation
(Hc), the water height in the piezometer (Hw) corresponding to
the pore water pressure at the base of the sedimenation, and the
excess pore water pressure height (He=Hw-Ht).
R&D Benefits from T&E Laboratory Tests
The author has been working for mining backfill for many
years, an area in which he has made several contributions (e.g.,
[5-9]). The consolidaton of fill materials in backfilled stopes is
a critical concern [10-14]. The T&E laboratory tests provided
the author with an opportunity to examine the self-weight con-
solidaton precess. A further review of the literature indicates
that self-weight consolidation is also a concern in coastal and
canal transporation engineering due to the disposal of dredged
materials [15-18]. It is also a crtical concern in management of
the surface disposal of mining tailings and fly ash [18-25].
An improved instrumentation (picture taken after 26 hours and
45 minuites of of self-weight consolidation).
A further investigation reveals that the T&E instrumention
presented here is very simple, but quite innovative in terms of
measurements of the evolution of the physical and hydraulic
properties of slurried deposition. This has lead to the publica-
tion of a peer-reviewed paper in which test result interpretation
details have been presented . In the following section, some
typical results will be shown to demonstrate the benefits to
R&D arising from the T&E laboratory tests.
1) Evolution of Physical Properties:
When the newly deposited backfill is submitted to drainage
and consolidation, its physical properties, such as the total den-
t) and the void ratio (e), change with time. At the mo-
ment of deposition, its initial total density (
t0) would be at a
minimum while its initial void ratio (e0) would be at a maxi-
The initia l density of the newly deposited backfill can be es-
timated as follows :
w is the density of water, Ht0 is the initial thickness of
the newly deposited backfill, Hw0 is the maximum water head
in the piezometer immediately following the deposition.
Equation (10) indicates that it is possible to obtain an esti-
mate of the initial density of the slurried sample by measuring
Hw0 and Ht0. This leads to
t0 = 1.33 g/cm3 with test results
presented in Li et al. .
Once the initial total density (
t0) is obtained, the total den-
t, of the consolidated deposition can be estimated as fol-
The void ratio, e, of the newly deposit ed backf ill is esti mated
by the following equation:
s is the density of the solid particulate. For most cases,
its value can be taken as 2.7 g/cm3.
Figure 8 shows some results of the evolution of the void ra-
tio (e) and the total density (
t) of the newly deposited backfill.
0100 200 300 400 500
) an d e
Elaps ed ti me (hours )
V oid ratio
Evolution of ph ysical properties due to self-weight
consolidation of newly deposited backfill.
Copyright © 2012 SciRes.
It can be seen that the void ratio decreases while the total den-
sity increases with the time of self-weight consolidation.
2) Evolution of Pore Water Pressures and Stresses
With the instrumentation presented here, the pore water
pressure, uw, and the excess pore water pressure ∆u, at the base
of the deposition can be readily obtained as follows:
where g (= 9.81 m/s2) is the gravity accelerator.
The total vertical stress,
v, at the base of the deposition can
be estimated with the following equation ,
while the vertical effective stress,
'v at the base of the deposi-
tion is estimated by the following equation:
Figure 9 illustrates the evolution of (excess) pore water
pressures and (total and effective) stresses at the base of the
newly deposited backfill. It can be seen that the pore water
pressure and the excess pore water pressure decrease at the
same pace with the time of self-weight consolidation. Regard-
ing the vertical stresses, the total one decreases while the effec-
tive one increases with time of self-weight consolidation.
Within the tested period, the difference between the total and
effective stresses remains significantly high, indicating that the
drainage and consolidation process are still far from complete.
2) Evolution of Hydraulic Properties
The hydraulic conductivity (or coefficient of permeability), k,
is an important parameter in drainage and seepage calculations.
Considering Darcy’s flow, the hydraulic conductivity can be
obtained by the following equation:
where v is the flow velocity through the sample, and i is the
hydraulic gradient. With the instrumentation presented here,
they can be obtained by the following equations:
where ∆t is the time interval between two time point s of meas-
urement, ∆(Ht – Hc) is the thickness variation of the decantation
water during the period ∆t.
Figure 10 shows the evolution of hydraulic conductivity of
the newly deposited backfill estimated from experimental re-
sults. It can be seen that the hydraulic conductivity decreases
quickly at the early stage of self-weight consolidation, and
tends to become constant after about 200 hours of consolidation.
The figure also plots a description proposed by Li et al. . It
can be seen that the proposed equation describes the experi-
mental data quite well.
The results presented above stem from a very simple instru-
mentation aimed at providing a visualizion of excess pore water
pressure during the self-weight consolidation of a newly depos-
ited backfill. The instrumentation was initially designed for
T&E purposes. The results presented above clearly show that
this target is achieved.
Furthermore, it has been shown that the laboratory test
method presented here can be used to measure a variety of
physical and hydarulic properties of slurried depositions under
self-weight consolidaton. Compared to existing test methods
for measuring slurried deposition physical and hydraulic prop-
erties [4, 15-16], the method presented here has an important
advantage: no external hydraulic or mechanical solicitation is
applied. Consequently, the state of the deposition is not dis-
turbed during the test. Results obtained with the proposed
method should be more representative than with existing
Of course, the instrumentaion presented here is still far from
perfect. More work is needed to improve the testing method.
Nonetheless, the results shown above clearly demonstrate the
R&D benefits from T&E.
Stresses and pressures (Pa)
Elapsed ti me (hours)
Vertical total stress
Vertical effective stress
Pore water pressure
Excess pore water pressure
Evolution of (excess) pore water pressures and (total
and effective) stresses at the base of the newly depos-
0100 200 300 400 500
Elapsed ti me ( hours)
Evolution of hydraulic condu ctivity of th e newly dep os-
ited backfill estimated f rom measurement an d describ ed
with an equation proposed in Li et al. .
Copyright © 2012 SciRes.
The benefits of T&E for R&D have been shown. Doubtless,
T&E and R&D are two individable c omponents for a university
professor who has the obligation to transfer knowledge from
generation to generation, and the mission to advance human
knowledge. As an integrated professor, equilibrium should be
granted to both aspects and effforts should be encouraged on
The author acknowledges the financial support of the École
de technologie supérieure (FIR, PSIRE-recherche, and FDETS)
and the Natural Sciences and Engineering Research Council of
Canada (RGPIN). The laboratory tests were realized by J.D.
Aubertin, I.C. Alvarez and C. Kéchichian. Support from the
Department of Construction Engineering (G. Lefebvre, S.
Bélisle, and C. Lavoie) is acknowledged.
NSERC, Discovery Grants Information Centre. Natural Sciences and
Engineering Research Council of Canada, 2011.
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