1. 1
ATS11-05415
1. INTRODUCTION
Underground infrastructures including macro and micro
tunnels such as subway tunnels, mining tunnels, water, gas &
oil supply tunnels, sewer and culverts are always expensive to
build, repair and maintain but are essential for the wealth
creation and development of the nations. Therefore, they must
be built with a long term design life which is related to
structural and waterproofing stability of tunnel.
The soil which is covered the underground tunnels
contain a variety of corrosive materials [10], [12]. Thus, when
groundwater penetrates towards the tunnel it can absorb all
these aggressive materials from the soil. Hence, direct contact
between this aggressive water with the main waterproofing
membrane causes major damages to waterproofing system of
the tunnel (Figure 1). Then, after seepage through the main
waterproofing membrane, this corrosive water by penetrating
into fabric of the tunnel final lining can cause steel
reinforcement corrosion and concrete cracks (Figure 2). As a
result, the water leakages start to damage the final concrete
structure just a few years after construction of the tunnel.
As we can see in Figures 1 and 2, the common problem in all
existing underground tunnels is the lack of a primary water
reducing system.
ABSTRACT
According to investigations conducted on the existing underground tunnels, one of the most primary
problems observed in these infrastructures is water leakage due to the penetration of water through
damaged waterproofing system and final lining. While the water infiltrate through the soil, there is a high
probability that corrosive materials such as acids and sulfates may dissolve in the water. As a result,
waterproofing membrane starts corrosion after contact with corrosive water and tunnel will experience
irreparable structural damages such as steel reinforcement corrosion and concrete cracks. Hence, the major
problem in all existing underground tunnels is the direct contact between high volumes of aggressive water
with the main waterproofing membrane without any defense opportunity. Execution of a watertight
temporary support (WTS) right after each partial excavation can be a proper solution to this problem. The
objective of this paper is to demonstrate the positive roll of WTS in improvement of tunnel waterproofing
performance. In this study the standard test method ASTM C 642 has been carried out to estimate the
porosity and pore volume in concrete specimens. Furthermore, a cement based polymer was added to test
mortar mixture to reduce the porosity and permeability of hardened specimens. According to the final
results, percentage of volume of permeable pore space or porosity (ɸ) less than 11% was achieved for
mortar specimens which were contained 7.5% to 20% acrylic polymer modifier (APM) while the porosity
of reference specimen was 14.42%. Additionally, the best result was obtained for the test mortar specimen
which was contained 12.5% APM, with 9.78 % porosity.
KEYWORDS
Corrosion; Permeability; Porosity; Shotcrete; Temporary support; Tunnel waterproofing membrane.
Improvement of Tunnel Waterproofing Performance by Execution
of Watertight Temporary Support (WTS)
N. Ghafari
Department of Civil & Environmental Engineering, Mapúa Institute of Technology, Manila, Philippines

2. 2
Figure 1: Water infiltration through the soil and temporary support
Figure 2: Water penetration through the final lining structure
This paper recommends the use of watertight temporary
support (WTS) system as an innovative waterproofing method
(Figure 3) to control the corrosion and leaking in underground
tunnels in future. This method employs a waterproof
concrete/mortar mixture to spray on the excavated parts of the
tunnel by shotcrete operation and provide a primary water
reducing barrier before execution of the main waterproofing
membrane and final lining. This is to reduce the volume of
aggressive water before contact with the main waterproofing
membrane.
In construction of underground spaces such as highway or
subway tunnels, except in shield tunneling method, the soil
around the excavated parts of tunnel should be protected by
execution of a temporary support immediately after each
excavation process. This is to prevent the falling of any debris
and reduce the risk of settlement before the execution of
tunnel final lining. This will be a good opportunity to provide
a primary water resistant barrier by adding a suitable concrete
waterproofing admixture to the shotcrete mixture. In fact, the
greatest advantage of this proposed waterproofing system is
that, there is no additional shotcrete operation cost for
execution of watertight temporary support (WTS).
Figure 3: WTS waterproofing system
In this study a cement based polymer was used to produce
a water resistant mortar mixture for test specimen preparation.
Different ratios of acrylic polymer modifier (APM), as a
typical waterproofing admixture, were added to the mortar
mixture to determine the optimum amount of APM for
achieving the lowest porosity and permeability. Since,
underground temporary structures (supports) are always
covered by the final lining structure during construction of
tunnel; preparation of specimens from a real underground
shotcrete structure was not possible. The methodology section
of this paper was focused on the laboratory concrete test
(ASTM C 642) [9] on cylindrical mortar specimens (5 × 10
cm) prepared in accordance with ASTM C 1438 [5], C 1439
[6], C 192 [7], and C 470[8].
2. REVIEW OF RELATED LITERATURE
Waterproofing of underground structures has been a
subject of concern to many professionals for thousands of
years [22]. Recent researches in the field of tunnel
waterproofing methods and materials can be divided into two
different categories [11], [14], [15], [17], [20], [23]:
2.1. Developments in the field of waterproofing materials
and membranes
The first group of researchers study on the new
waterproofing materials for execution of tunnel waterproofing
system. This group believes that they can achieve a secure
tunnel waterproofing system by developing in the field of
waterproofing materials such as epoxy, liquid and sprayed
waterproofing materials or sheet membranes like PVC sheets.
2.2. Developments in the field of concrete waterproofing
admixtures
The second group of researchers study on the new concrete
admixtures to attain a proper waterproof concrete for
execution of tunnel final lining. This group believes that they
can produce a secure waterproof concrete that could be able to
cover the tunnel as a suitable waterproofing system without

3. 3
any need of other waterproofing materials and membranes.
However this method should not be generalized for any
condition related to depth below water table and chemical
aggressivity of the ground water. Waterproof concrete method
is primarily used in Asia and has been used in Singapore on
the MRT.
3. CONCRETE LABORATORY TEST
The ASTM C 642, standard test method for density,
absorption, and voids in hardened concrete, is recommended
by the National Concrete Pavement Technology Center at
Iowa State University (2008) to determine the porosity of a
portland cement concrete structure. The porosity and
permeability of reinforced concrete structures are the major
factors for long-term durability particularly in underground
spaces. ASTM C 642 estimates the volume of permeable pore
space as well as the porosity (ɸ) of hardened concrete
specimens by determining the density of specimens in three
different states of oven dry, saturated and saturated-boiled. A
chart has been provided (Figure 5) which shows the test
processes from specimen preparation to the final calculations.
3.1. Mortar specimen preparation
A total number of 27 specimens (nine different mortar
mixtures and from each mixture three specimens) in the form
of cylinder (5 × 10 cm) were provided (Figure 4). Moreover,
different ratios of acrylic polymer modifier (APM) were added
to test mortar mixtures as a concrete admixture for preparation
of test mortar specimens.
Figure 4: Specimen preparation
The specimen preparation established according to ASTM
C 1439 (Standard test methods for evaluating polymer
modifiers in mortar and concrete) [6], ASTM C 192 (Standard
practice for making and curing concrete test specimens in the
laboratory) [7], and ASTM C 470 (Standard specification for
molds for forming concrete test cylinders vertically) [8]. Table
1 is provided below to show a summary of mixture proportion
for each prepared mortar specimen.
Figure 5: Concrete test processes
Table 1: Summary of mixture proportion of each specimen
Specimen APM W/C Sand
Portland
Cement
Water
S1 0% 70%
1210
(61.80%)
440
(22.47%)
308
(15.73%)
S2 2.5% 70%
1210
(60.29%)
440
(21.92%)
308
(15.35%)
S3 5% 70%
1210
(61.80%)
440
(22.74%)
308
(14.98%)
S4 7.5% 70%
1210
(57.49%)
440
(20.90%)
308
(14.63%)
S5 10% 70%
1210
(56.18%)
440
(20.43%)
308
(14.30%)
S6 12.5% 70%
1210
(54.93%)
440
(19.98%)
308
(13.98%)
S7 15% 70%
1210
(56.18%)
440
(20.43%)
308
(13.68%)
S8 17.5% 70%
1210
(52.59%)
440
(19.13%)
308
(13.39%)
S9 20% 70%
1210
(51.50%)
440
(18.73%)
308
(13.11%)

4. 4
3.2. Determination of Oven-Dry Mass
After the mass determination all 28 day specimens were
placed in the electrical oven and the temperature was set on
104°C to oven dry the specimens for 24 hours (Figure 6). After
the first 24 hours, oven dried specimens were removed from
the oven and they were allowed to cool in dry air to a
temperature of 22 to 24°C. Then the mass of each specimen
was determined and recorded.
Figure 6: Specimens in electrical oven for oven drying process
The recorded mass of specimens showed that specimens
were still wet and need redrying since the differential in the
determined mass was more than 0.5% of the lesser value.
Therefore the specimens were returned to the oven for an
additional 24 hours drying process. A same procedure was
applied for the second oven drying. This time the differential
in the determined mass was not exceeded 0.5% of the lesser
value. Hence, this last value was designated “A”.
3.3. Determination of Saturated Mass after Immersion
At the second step, all specimens were immersed in the
potable water at approximately 21°C for three times (Figure 7).
Figure 7: Immersing the specimens in water
In the first immersion specimens were immersed for 48
hours. Then, specimens removed from the container and after
mass determination were returned to the water for the second
immersion (24 hours). Finally after the third immersion (24
hours) increase in the determined mass was not exceeds 0.5%
of the larger value. The specimens were immersed in the water
for the total time of 96 hours (48 + 24 + 24 = 96) and the last
determined value was designated “B”.
3.4. Determination of Saturated Mass after Boiling
After the last immersion, surface drying and mass
determination all specimens were boiled in a steel container
for 5 hours (Figure 8).
Figure 8: Boiling the specimens in steal container
After 5 hours boiled specimens were removed from the
container and allowed to cool by natural loss of heat for 18
hours to achieve a final temperature of 22°C. The surface
moisture was removed and the mass of each specimen was
determined. This soaked, boiled, surface-dried mass
designated “C”.
3.5. Determination of Immersed Apparent Mass
After immersion and boiling the specimens were
suspended in the water using a suitable wire to determine the
apparent mass of each specimen (Figure 9).
Figure 9: Suspending the specimens in water
To achieve the adequate values of apparent mass an
especial technique was used in this part of test. First a small
deep bowl filled with tap water and placed on the electronic

5. 5
scale and then, scale was set on the zero. Specimens one by
one suspended in the water by a wire and weights were
recorded and designated “W”. The following equation has
been used to determine the apparent mass for each specimen:
Apparent mass (g) = C (g) – W (g) (1)
where C is the recorded weight of each specimen after boiling
and before suspending and W is the recorded weight during
suspension of specimens in the water.
For example, for specimen number 1-1 (S1-1) we have:
Apparent mass of S1-1 (g) = C1-1 (g) – W1-1 (g) (2)
where C₁ˍ₁ is the recorded weight of S₁ˍ₁ after boiling and
before suspending and W₁ˍ₁ is the recorded weight during
suspending the S₁ˍ₁ in the water.
3.6. CALCULATIONS
By using the values of determined mass in accordance with
the procedures described above, the following calculations [9]
have been applied for all specimens separately and the results
of porosity are cited in Table 2.
Absorption after immersion, % = [(B – A) / A] × 100 (3)
Absorption after immersion & boiling, % = [(C – D)/A] × 100 (4)
Bulk density, dry = [A / (C – D)].ρ = g1 (5)
Bulk density after immersion = [B / (C – D)].ρ (6)
Bulk density after immersion and boiling [C / (C – D)].ρ (7)
Apparent density = [A / (A – D)].ρ = g2 (8)
Porosity, % = [(g2 – g1) / g1] × 100 (9)
Or:
Percentage of voids, % = [(C – A) / (C – D)] × 100 (10)
4. RESULTS AND DISCUSSION
The results of calculations show reduction in porosity of
mortar specimens (ɸ) from S1 to S6 and a little increase from
S6 to S9. Note that all specimens had a same w/c ratio (0.7)
and same materials (except ratio of APM) and tested in same
environmental conditions. S1 was the reference (ordinary)
concrete specimen which was not contained any waterproofing
admixture while S2, S3, S4, S5, S6, S7, S8 and S9 were test
specimens which were contained the amounts of 49 to 391.60
g acrylic polymer (2.5% to 20% of (cement + sand + water)).
The results show an adequate reduction in porosity of concrete
for S6 compare with S1. The mass determination charts in
different steps of concrete test have been provided for
specimen number 1 (S1) as the reference specimen and
specimen number 6 (S6) as the test specimen with the best
result (lowest porosity) in Figures 10 and 11.
Porosity reduction = ∆ɸ = ɸ (S1) – ɸ (S6) (11)
∆ɸ = 14.42 % – 9.78 % = 4.64 % (12)
In fact, S6 had the most porosity reduction and it has shown
the best result in this laboratory test compare with other test
specimens between S2 to S9 (Figure 12). Therefore, the amount
of 12.5% of concrete/mortar mixture (11.11% of total mass of
mixture) is the optimum usage for the APM (Acrylic Polymer
Modifier) to achieve the best results for waterproofing
stability of a shotcrete coating with thickness of approximate
average of 100 mm (Figure 13).
Table 2: Summary of test results and porosity for S1 to S9
No. A (g) B (g) C (g) D (g)
porosity
(ɸ)
S1 400.02 441.35 431.83 211.29 14.42%
S2 382.79 419.05 411.61 196.91 13.42%
S3 400.57 434.82 427.32 206.49 12.11%
S4 389.25 419.74 412.54 199.52 10.93%
S5 383.96 411.85 405.69 194.81 10.30%
S6 378.30 404.14 398.20 194.69 9.78%
S7 380.95 407.36 400.88 197.49 9.80%
S8 381.61 408.48 401.57 198.42 9.83%
S9 387.36 414.97 407.65 201.73 9.85%
Figure 10: Mass determination chart for S1 in different conditions
0
50
100
150
200
250
300
350
400
450
500
Massofspecimen(g)
Different parts of the concrete permeability test
Specimen 1-1
Specimen 1-2
Specimen 1-3

6. 6
Figure 11: Mass determination chart for S6 in different conditions
Figure 12: Different percentages of porosity achieved for S1 to S9
Figure 13: Different porosities achieved for different APM content
As shown in last two charts increase in the ratio of APM
does not correspond to porosity reduction for S7, S8 and S9. In
this case always the optimum ratio of admixture should be
determined for the concrete/mortar mixture to achieve the best
result (lowest permeability) with the lowest cost of materials.
The figure 12 shows that using the ratios above 12.5% APM
will just increase the cost of WTS system without any positive
effect.
5. CONCLUSION
According to the final results of concrete test, the porosity
(ɸ) less than 11% were achieved for the mortar specimens
which were contained 7.5% to 20% acrylic polymer modifier
while the porosity for reference specimen was 14.42%. In
addition, the best result (lowest porosity) was obtained for the
test mortar specimen which was contained 12.5% APM, with
9.78 % porosity. The percentage of volume of permeable pore
space (porosity) below or equal to 12% is desirable to achieve
a long-term durability for concrete structures such as
underground temporary supports.
By comparing the porosity of polymer modified specimens
with the porosity of reference specimen, this study has
demonstrated the positive effects of using acrylic polymer
modifier (APM) as an appropriate admixture for porosity and
permeability reduction in the hardened concrete/mortar
structures such as tunnel‟s temporary support and final lining.
The test results show that we cannot expect a continuous
reduction in porosity of concrete structures by increasing the
ratio of APM in the concrete/mortar mixture. In this case, the
optimum ratio of APM should be determined for the concrete
mixtures by conducting the appropriate concrete test. This is
to reduce the cost of tunnel waterproofing projects (cost of
admixture) and also achieve to the lowest porosity and
permeability for tunnel concrete structure at the same time.
The results of this study demonstrate that the WTS
waterproofing system can minimize the volume of aggressive
water before contact with the main waterproofing membrane
and final concrete structure in underground tunnels. As a
result, the performance of underground tunnels will improve
and their service life will become longer.
The cost of execution of WTS system is reasonable since in
underground tunneling methods, except shield tunneling
method, execution of a temporary support right after each
partial excavation is always a part of these conventional
tunneling methods. Hence, by adding an appropriate amount
of admixture (optimum amount) to the shotcrete mixture we
can simply replace the conventional method by the new WTS
waterproofing system without any additional execution and
labor costs.
6. ACKNOWLEDGMENT
I would like to express my deep and sincere gratitude to
Dr. Jonathan W.L. Salvacion the dean of graduate school at
Mapúa Institute of Technology for all helps and supports
during the preparation of this paper.
0
50
100
150
200
250
300
350
400
450
Massofspecimen(g)
Different parts of the concrete permeability test
Specimen 6-1
Specimen 6-2
Specimen 6-3
14.42%
13.42%
12.11%
10.93%
10.30%
9.78% 9.80% 9.83% 9.85%
0%
2%
4%
6%
8%
10%
12%
14%
16%
S1 S2 S3 S4 S5 S6 S7 S8 S9
Porosity(ɸ)
Specimens
14.42%
13.42% 12.11%
10.93%
10.30%
9.78%
9.80%
9.83%
9.85%
0%
2%
4%
6%
8%
10%
12%
14%
16%
0 0.025 0.05 0.075 0.1 0.125 0.15 0.175 0.2
Porosity(ɸ)
Ratio of APM

7. 7
I would also like to thank Prof. Bernard Villaverde the
faculty of the Civil & Environmental Engineering Department
and also the coordinator of the material laboratory at MIT.
And I would like to thank my dear friends Iman Mir and
Farkam Mohebi who were always beside me in the material
laboratory to help me in conducting the concrete test.
And finally special thanks to my dear family who always
support and help me to achieve my goals and wishes in my
life.
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