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

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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

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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%)

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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

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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

Mas

s of

spec

imen

(g)

Different parts of the concrete permeability test

Specimen 1-1

Specimen 1-2

Specimen 1-3

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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

450M

ass

of

spec

imen

(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

Poro

sity

(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

Poro

sity

(ɸ)

Ratio of APM

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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