Large-Scale Transmission Tunnel Rehabilitation Project for

1 INTRODUCTION

1.1 Tunnel at the outset

The Metropolitan Waterworks Authority (MWA) was one of leading firms in Thailand which had employed Tunnel Boring Machines (TBM) extensively in construction of its transmission system, throughout the past 30 years. Various TBM types, including, manual, semi-mechanical, mechanical and EPB were employed in tunneling projects with diameters of TBM ranging from 3.16 to 4.56 m., for the construction of tunnel ID ranging from 2.0 to 3.4 m. The tunnels were constructed mostly in a stiff clay layer at 17-20 m. from ground surface, but some went down to 30 m., when running across Chao Phraya River.

1.2 New Era of Water Transmission Tunnels

Tunnelling becomes a common practice for MWA. EPB (Earth Pressure Balanced) shield machines were employed, enabling excavation in all types of soil profile of Bangkok possible. Having been equipped with higher efficiency back-up system, such as GYRO, the excavated alignment could be easily controlled. Newly developed segments, both steel and RC, straight and tapered, facilitate tunneling through all radius of curvature, some cases, R < 50m. Recently, MWA succeeded in projects under the 7

th Bangkok Water Supply

Improvement Project with total length of 50 km. of tunnels constructed and 14 EPB TBMs adopted.

Large-Scale Transmission Tunnel Rehabilitation Project for Sustainable Water Supply Management in Bangkok Urban Area

A Case Study of Metropolitan Waterworks Authority Bangkok, Thailand

D.Klahan & B.Vongsa & M.Panaim & P.Traidate & W.Phakjarung Metropolitan Waterworks Authority, Bangkok, Thailand

ABSTRACT: Metropolitan Waterworks Authority (MWA) has been involving in the construction of underground tunnel using Tunnel Boring Machine (TBM) for more than 30 years. Treated water has been conveyed through the large-scale transmission tunnel networks, with the total length of 187 kilometers, to the distribution pumping stations around and inside the metropolitan boundary. At the outset, the typical tunnel sections, both primary and secondary linings, were designed to be reinforced concrete. Having been in use for long term, there are some leakages detected, which caused severe effect to the road surface and to some extents to the above ground structures. MWA, therefore, launched the tunnel rehabilitation project, comprising of 4 routes, with total length of 14 km, with an aim at surveying the leakage points by employing the so-called Geophysical Surveying Method, filling the voids detected along tunnel alignment with proper materials and installing Steel Pipes (MS-Tube) inside the existing tunnels as secondary lining to strengthen the structure and to increase water pressure resistant capability.

This paper is aimed at describing the method of Tunnel rehabilitation, which has been acceptably and technically proven to be one of the proper solutions for rehabilitation of large-scale tunnel, since it was once successfully adopted in the previous tunnel repair project from Bangkhen Water Treatment Plant to Pradipat Valve Chamber. Such repaired tunnel has been in use well until now without any leakage encountered. Pipes inserted inside of tunnel were electrically welded, then, infilling mortar was grouted into the annulus around the inside of tunnel and outside of inserted pipes, leading to final tunnel section with considerably higher sectional modulus. Some challenges, for example, when performing underground works nearby the MRT Tunnel and preventive measures to cope with which employed FEM analysis in conjunction with installation of a series of geotechnical instrumentation as well as setting out the Trigger Level for monitoring, were also discussed.

Keywords : Tunnel Boring Machine (TBM), Transmission Tunnel, Primary Lining, Secondary Lining, Rehabilitation, Geophysical Method, Steel Pipes, FEM Analysis, Instrumentation, Trigger Level

1.3 Background of the problems

The initial east-bank water transmission network consisted of tunnels built solely from Reinforced Concrete. Unlike the modern tunnels, olds tunnels were without internal steel linings. (Figure 1). A problem that may arise when an underground leakage enlarges, is Sink Hole underneath the roads (Figure 2) Sink Hole may cause the road’s structure or nearby buildings to collapse. It may also cause further damage to tunnel structure itself. Damage caused water loss accounted for millions bath per year. Most severely, water supply network may come to halt, bringing unpleasant effects on the capital

Figure 1 Typical Tunnel Section

Figure 2 Sink hole caused by water leakage

2 TUNNEL REHABILITATION PROJECT

2.1 Coping with problems

According to the leakage points recorded during operation, where there were up to 25 locations found and likely more without visible evident, MWA has planned for the measure to cope with such problems. Exact location of all possible leakage points, both visible and invisible, needed to be extensively surveyed. Since employing steel lining as a secondary lining is most optimised

technique for the construction of large-scale water tunnels, nowadays, and, since, MWA had experience in choosing to insert the steel lining for the rehabilitation of some early water tunnels with success. Thus, MWA is relying on the same technique for the rehabilitation of existing tunnels for the current project. MWA, Therefore, decided to launch a project namely G-TN-R2-7(R) under the 7

th

Bangkok Water Supply Improvement Project to rehabilitate the leaked Tunnels.

2.2 Details and scope of the project

The works under this contract are consisted of

rehabilitating 4 sections of existing tunnels as shown

in Figure 3 including;

Section 1: Tunnel Diameter 2.5 meters, from

Si Phraya Valve Chamber to Lumpini Valve Chamber

with approximate length of 2.4 kilometers.


Pradipat Valve Chamber to Si Phraya Valve Chamber


Section 3: Tunnel Diameter 2.0 meters, from Lad

Ya Riser Structure to Tha Phra Riser Structure with

approximate length of 3.7 kilometers.


Lumpini Valve Chamber to Lumpini Drop Structure


Figure 3 Project location map

The construction period started from November

2010 to October 2013. First, works in section 1 in

conjunction with section 3 were performed at the

same time, followed by works in section 2 and

finally works in section 4.

The total contract price is 762,189,530 Baht.

The Contractor is Italian-Thai Development Public

Company Limited. Construction is supervised

jointly by MWA and the specialized consultant

including Asdecon Corporation and Geotechnical

and Foundation Engineering co.ltd. The scopes of the works are as follows;

1. To locate the leakage points along the whole

tunnel line using the geophysical method and to fill

the voids caused by leaked water with appropriate

materials. Two alternatives of geophysical methods

including Ground Penetration and Resistivity Test

were considered. The latter was selected to survey

the voids along the tunnel line since it could provide

more accurate information for the specific depth of

tunnel (approximately 17-20 m. from surface) This

method adopted the concept of difference electric

current measured in the different media. The area

where there was leakage (high moisture content)

would show lower Resistivity value than those

measured from soil or sand. Conventionally, the

Resistivity (Ohm-m) got from measurement through

soil ranged from 1-1,000, while the value got from

sand ranged from 1-100 and value got from ground

water ranged from 0.5 – 300. When plotted as

detour, lower Resistivity zone (higher moisture

content) would give blue color. The measuring

equipment and example of results are as shown in

Figure 4.

Figure 4 Resistivity test for leakage point

Figure 5 Example of the leakage survey result

From Figure 5, it was found that Resistivity test

gave the result with acceptably good agreement with

the existing leakage point information. Having done

all survey along the route line, total 27 leakage

points were found. After the area with high tendency

to have tunnel leakage was primarily located, then,

Soil Boring Investigation was performed at every

leakage point. It was obvious that, the location of

tunnel leakage would give the higher moisture

content and lower SPT-N value.

At the design stage, the Consultant, Asdecon

Corporation and Geotechnical and Foundation

Engineering co.ltd (Asdecon & GFE), had

performed the FEM analysis, and found that there

was significant effect from void around the tunnel to

the settlement of the ground and nearby structures

when shutting down the transmission system leading

to decreased pressure inside MWA tunnel. Thus,

such voids were needed to be filled before tunnel’s

shut-down. The FEM analysis was as shown in

figure 6.

Figure 6 FEM analysis to study the effect of

void when shutting down the transmission system

The schematic diagram of void filling process is

shown in Figure 7. One of materials used for filling

the voids was cement base with conventional

proportion per m3 as shown in Table 1. Such

proportion might be particularly adjusted to suit with

ground condition. In some cases, other appropriate

materials were used.

Figure 7 Void filling process

Material Weight (kg)

Cement

Bentonite

Water

350

52.5

870

Table 1 Typical void filling proportion (kg/m3)

2. To excavate and get the existing construction

shafts and valve chambers modified in order to give

ease for installation of Steel Pipes inside tunnels.

Some shafts that were backfilled and restored, were

modified and used as construction shafts for

Av

At

Medium

Clay

Stiff

Clay

Dense Sand

supplying pipes and grout car for secondary lining.

When all works finished, those shafts were again

restored to the existing condition (Figure 8).

Figure 8 Modification of existing shafts

3. To construct the by-pass piping systems at Si

Phraya and Lumpini Valve Chambers, in order to

cope with the shortage of water during shutting-

down of the transmission system and distribution

pumping stations for works under section 2 and 4

4. To install Steel Pipes inside the repaired tunnels

using electrical welding method, pour the infilling

mortar around the tunnel and pipe annulus and get

all the systems tested and disinfected before putting

in service. After tunnel’s shut-down, water inside

tunnel was drained out and tunnel’s inner surface

was thoroughly clean. It was found that, after being

used for years, the RC lining (secondary lining) of

the existing tunnel was in considerably good

conditions. There was an obvious de-scaling of

surface due to abrasion, but not very deep. The

previously repaired cracks which employed portion

of steel segment bolted and sealed to tunnel surface

were in good condition without severe damage and

excessive corrosion found (see figure 9). The cracks

were then surveyed and repaired by adopting PU

Foam, which could efficiently stop water from

outside of the tunnel. The application of PU Foam to

stop water is as shown in Figure 10. The ventilation

system, lighting system with emergency lights,

communication system and rails were, then, installed

inside the tunnel (Figure 11). In this project, the

Contractor decided to use low voltage electricity

system (380 V) instead of conventional high voltage

system (6.6 kV) inside tunnel. The advantage was

that it was unnecessary to provide transformer inside

tunnel, but required larger diameter of wire, leading

to higher installation cost, but with higher safety in

exchange.

Figure 9 Existing tunnel’s conditions after

draining out the water

Figure 10 Application of PU Foam to stop water

at existing tunnel’s cracks

Figure 11 Installation of ventilation & lighting

MS Tube was transported into tunnel on rail via

locomotive. Selection of proper rail type and size was

also of importance. Since clearance was limited, this

made conventional rail unsuitable. The channels (100 x

50) were adopted (see figure 12). Two types of

locomotives were used including electrical locomotive

and modified tow tractor (see figure 13). At the outset

of project, pipe carrier was designed to be carriage-like

which was very rigid (see figure 14). The carriage was

durable, but it took time to install pipe and rather made

some visible damage to inside surface of pipe. Later, it

was decided to change to simple roller-like carrier,

which could serve well, but needed more frequent

maintenance in exchange (see figure 15)

Figure 12 Rail made from channel 100x50

Figure 13 Modified tow tractor (Top) and conventional

electric locomotive (Bottom)

Figure 14 Pipe carriage

Figure 15 Roller-like pipe carriers

Prefabricated Pipes were transported to the

position where they would be electrically welded (see

figure 16). The annulus between outside of the pipes

and inside of tunnel was grouted by infilling mortar

(see figure 17). This mortar, when got harden, would

provide corrosion protection to the pipe as pH around

the pipe surface was increased in the same manner as

concrete providing the thin film protection for re-bar.

Tunnel’s sectional modulus was also significantly

increased.

Figure 16 Pipe transportation inside tunnel

Figure 17 Grouting of infilling mortar

Mortar grouting was controlled by pressure in

conjunction with volume measurement in order to

ensure that the annulus was filled completely. Grouting

material was specially mixed so that it could maintain

adequate workability at placing after being transported

inside tunnel and re-mixed by re-mixer car (see figure

18).

Figure 18 Set of equipment for infilling mortar

The mortar was designed to have slump flow more

than 60 cm. in diameter and target strength of 200 ksc.

The typical proportions of infilling mortar are as

shown in Table 2.

Material Weight (kg)

Cement

PFA (Fly Ash)

Water

Sand

Admixture

275

275

295

1460

45 (cc)

Table 2 Typical infilling mortar proportion (kg/m3)

MS Tubes (pipes) were connected through electrical

welding. The welded joints were tested by dyke

Penetrant test. After welding, joints needed to be

repaired and O\QC checked to ensure that same quality

as shop fabrication could be achieved. Tests, including;

Holliday detection test (2,000 v), Dolly Test (Epoxy

lining’s adhesion test) and Dry Film Thickness Test

(not less than 406 microns), were performed. Details

are as shown in figure 19.

Figure 19 On-site testing of MS tube’s internal lining

After passing pressure and disinfection tests by

MWA’s Water Quality Control Department, the

rehabilitated tunnel was ready to transmit water.

Tunnel repaired and inserted by MS tube is as shown

in figure 20.

Figure 20 Tunnel ready to be used

The average rate of pipes insertion, installation and

infill mortar grouting was 10.77 m./day for section 1

and 3, 13.56 m./day for section 2 and 11.80 m./day for

section 4. The rate of work of section 1 and 3 seemed

to be comparatively lower than those of the other two

sections because the works started first. At the outset,

the contractor encountered the problems in various

aspects, including; suitability of pipe carriage, grouting

equipment, suitability and size of steel made for rails,

maintenance of rails and locomotives and, of most

significance, the skills of workers and labors. Having

experienced the learning curve of methodology, the

rate was found to increase when undergoing works of

section 2 and 4.

2.3 Challenges and Findings : Rehabilitation nearby MRT’s Tunnels

The Effect of Rehabilitation Works to MRT Tunnels in adjacent area was taken into consideration very seriously. Prior to commence-ment of rehabilitation project, MWA needed to prove that its working conditions met the specified safety provision and tolerance of MRT. This is in accordance with MRT’s Act, that required other agencies to get permission to work in the MRT’s safety zone. Figure 21 shows that there are two MRT tunnels constructed on top and bottom of previously built MWA tunnel. At the time of construction of MRT project, ground improvement had extensively been carried out around MWA tunnel to mitigate the adverse effect from TBM’s driving. This time, there was a need to take water out of the MWA tunnel, so proper preventive measures were required to mitigate risk that might arise to MRT tunnels instead.

Place the cursor on the T of Title at the top of your newly named file an

Figure 21 Layout of MRT and MWA tunnels

The Consultant (Asdecon & GFE), as a designer, had performed extensive study using Finite Element Method (FEM) and found that, reducing pressure in-side MWA tunnel by draining water out such tunnel did not significantly affect the soil around and near-by both MWA and MRT’s tunnels (figure 22). The deformation and movement of MRT’s Tunnels was considerably small in such a way that it did not affect the serviceability of MRT’s Tunnels. It was found that the differential principle stress and differ-ential radial deformation were in acceptable limit (less than 25 kPa and less than 3 mm.). A series of instrumentation was requested to install to continual-ly monitor the ground movement both before and af-ter working. Trigger levels were set so that immedi-ate actions could be taken appropriately to tackle with problems that might arise.

Figure 22 FEM model & analysis to study effect of MWA tunnel when releasing pressure to MRT tunnels

3 CONCLUSIONS

Conclusions from the experience from this tunnel rehabilitation project can be drawn as follows;

3.1 Employing steel lining as secondary tunnel lining is considerably and acceptably optimised technique for the construction and rehabilitation of large-scale water tunnel.

3.2 Voids around tunnel at leakage points are likely the area which are soft and have higher moisture content. They are likely the small voids connected to one another rather than large single voids.

3.3 Taking into account of durability, primary lining of tunnel which was made of RC, in overall, was in acceptably good condition without severe damage, except where there were small cracks.

3.4 Geophysical method was effective way to indicate the area where are likely to have high moisture content. It can’t be employed to specifically locate the exact position of voids, but extended measures might be needed, such as boring.

3.5 This tunnel rehabilitation project, when finished,

could significantly reduce the volume of water

leakage and considerably increase the stability of

water transmission system enabling MWA to

manage the water supply to cover all service area

with higher efficiency and effectiveness. This would

make MWA to be in agreement with the ministry of

interior’s policy as well as to accomplish its mission

which is to provide “Quality Water for Quality Life”.

4. ACKNOWLEDGEMENT

The Authors would like express their sincerest gratitude and deepest appreciation to MWA Governors, Mr. Charoen Passara and Mr. Thanasak Watanathana and Deputy Governors (Engineering and Construction), Mr. Luechai Deethavorn and Mr. Vitaya Intachit for their supervision, guidance,

encouragement and leadership during the project duration.

Sincere thanks are also extended to Italian-Thai Development Public Company Limited, especially, Mr.Supak Khunviriya, Prject Manager, for good cooperation throughout the project.

The Author would like to thank Asdecon and GFE, as Consultant, for their assistance in design checking, performing FEM analysis and remedying the technical problems encountered during the project.

Finally, the authors would like to record their appreciation to the Metropolitan Waterworks Authority (MWA) for supporting this project.

5. REFERENCES

Thailand Underground and Tunnelling Group, 2012.

Tunnelling and deep excavation works in Thailand.

N. Phienwej & Z.Z. Aye & A. Sramoon & T.Juirnarongrit

& T. Srisirirojanakorn & A. Asanprakit., (eds.).,

International tunneling and Underground Space

Association, World Tunnel Congress 2012 & 38th General

Assembly, Underground Space for a Global Society,

Bangkok, 18-23 May 2012.

Thailand Underground and Tunnelling Group, 2012. Water

Supply Tunnels. T. Kongsomboon (ed)., Tunneling and

Underground Spaces in Thailand.

17.0

0 m

.

24

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m.

10

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Fill

Soft Clay

Medium Clay

Stiff Clay

Dense Sand

Stiff Clay

Medium Dense Sand 1

Stiff Clay

Medium Dense Sand 2

Medium Dense Sand 2

Hard Clay

MRT

MRT

MWA

3.0 m.

7.5 m.

3.6 m.

5.3 m.

1.2 m.

3.4 m.

1.1 m.

4.6 m.

1.2 m.

6.1 m.

4.0 m.

7.3 m.

Documents

Large-Scale Transmission Tunnel Rehabilitation Project for