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Tunnelling and Pipejacking Techniques forTrenchless Installation of Drainage Pipelines

Hong Kong, a city on hilly natural terrain, with a total area of 1,000 square kilometres, hasa population of 7 million. Its developments mainly concentrate in 20% of the flat land in the

coastal area, mostly formed by reclamation from the sea. The rapid economic growth in the last

20 years demands new infrastructure and upgrading of existing facilities. The crowded spaghetti-

like complex of existing utilities and services underground in the limited road space, and the

busy traffic, make such upgrading and construction of new features, by the conventional open-

trench method, difficult. The use of tunnelling and pipejacking techniques could however resolve

most of the problems associated therewith, such as disturbance to traffic, major diversions of

existing utilities, earth moving, and effect of inclement weather. This would also minimise public

complaints due to inconvenience and loss of business in the nearby shops as temporary traffic

management schemes are only required at the jacking and receiving shaft locations. This paper

discusses the various types of tunnelling and pipejacking techniques adopted in Hong Kong

for drainage pipeline construction under different site constraints and ground conditions, theirperformance, the problems encountered and the recommendations made.

Keywords: Shaft Construction, Hand-dug Tunnels, Heading Construction, Earth Pressure

Balance Method, Slurry Pressure Balance Method, Tunnel Boring Machine,

Ground Settlement, Control of Tunnel Alignment, Rescue Operation

Wilson W S MOKMeinhardt (C&S) Ltd

K W MAKDrainage Services Department,

Government of the HKSAR

The Hong Kong Institution of Engineers Transactions, Vol 16, No 2, pp16-27

Introduction

The roads in the urban areas of Hong Kong are generally congested with

underground utilities and services of different types and sizes, at different

depths. To meet the development demand, new features are constantly

added and existing installations are upgraded over the years. This forms

a spaghetti-like complex network, causing problem to accommodate morenew installations due to lack of sufficient space. Diversion of existing

utilities and services to give room for such installations is difficult as other

locations in the vicinity may also be crowded with utilities and services. In

the past, the installations were commonly carried out by the conventional

open-trench method, requiring the implementation of temporary traffic

management schemes (TTMSs). These TTMSs are usually limited to no

more than 20 - 30 m in length in each stage, depending on whether

existing buildings are located adjacent to the works site, due to the

requirement of allowing space for access of fire engines under emergency

situations, and other factors, such as access to shops or premises. This

limited length of TTMSs could only allow limited utility diversion, and

therefore may not effectively resolve the problem. At some locations,

the underground is congested with existing utilities and services in

layers, rendering such new Installations by the conventional open-trench

method impossible. Tunnelling and pipejacking can however minimise

such effects as road openings are only restricted to the shaft locations,

ie jacking shaft and receiving shaft between a pipeline, which can be

selected to avoid conflicting with traffic and major utilities or minimise

their diversions. Sometimes, tunnelling and pipejacking techniques are

adopted solely to minimise traffic disruption, in extremely busy areas,

or in response to public requests or complaints on the same concern,

or even to avoid the felling of valuable trees.

Pipejacking is a technique of pipeline installation, by hydraulically pushing

a pipe string, effected either mechanically by a tunnel boring machine

(TBM) or manually for excavation, from a jacking shaft to a receiving

shaft. Jacking pipes are then added one after another to the end of the

pipe string as the preceding pipe/TBM advances. The excavated materials

are then transported to the jacking shaft through a trolley system, forhand-dug tunnels and earth pressure balance (EPB) TBMs, and then

lifted up to ground surface, or by a slurry discharge pipeline for slurry

operated TBMs. This procedure is repeated until the pipe string reaches

the receiving shaft [1].

The history of using pipejacking techniques for constructing drainage

pipelines in Hong Kong is short, with the track record in 1989 that

370 m of sewers, in diameter of 1,350 mm, located 6 - 14 m below

ground, were constructed by TBMs under 5 drives, with a length rangingfrom 40 to 80 m, passing beneath major roads [2]. Since then, the scale

of pipejacking works has increased significantly, with the deployment of

different types of TBMs operating in different modes, to account for the

ground conditions likely to be encountered, and also the introduction

of hand-dug tunnels for constructing pipelines crossing old seawalls and

congested utility zones, or ground susceptible to artificial obstructions.

In some projects, some of the works by open-trench may need to be

changed to tunnelling and pipejacking techniques during the construction

stage, to suit constraints of traffic and existing utilities, and such is usually

carried out by means of heading construction due to its simple setup

and fast operation. Up to 2002, more than 14 km long pipelines, with

a diameter range of about 450 - 3,000 mm, using such techniques,

have been completed by the Drainage Services Department (DSD) of

the Government of the HKSAR [3].Between 1996 and 2006, some of the notable projects employing

tunnelling and pipejacking techniques were the West Kowloon Reclamation

Hinterland Drainage Package 2 (Northern Portion) (with a length of more

than 1 km), the Central, Western and Wan Chai West Trunk Sewers (with

a length of 6 km), the Aberdeen, Ap Lei Chau and Pok Fu Lam Sewerage

Stage 1B (with a length of 2 km), and the Wan Chai East and North

Point Sewerage Trunk Sewers (with a length of 4 km), under different

geological conditions and depths.

The Wan Chai East and North Point Sewerage Trunk Sewers was the first

DSD project using slurry operated TBMs to construct curved sewers with

a minimum radius of 320 m, and a S-shape sewer (404 m long), with a

combination of straight and two curved sections (of radius 500 m) and

passing through an intermediate shaft and launching into the receiving

shaft, both with the completion of the permanent shaft in advance [4].

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Some other projects also use pipejacking or heading techniques but in

a much smaller scale.

Geological Conditions

The geological conditions in Hong Kong soils are highly variable in a

short length. The narrow strip of land along the seafront, adjacent to very

steep slopes, has been formed by cut and fill techniques in the terrain

over the years, and generally consists of a thin layer of fill underlain

by colluvium and completely to highly weathered granite near the hills

to a thick layer of fill, with different contents of boulders at differentdepths, overlying marine deposits, alluvium and completely to highly

weathered granite towards the sea. Depth to bedrock ranges from 1 to

2 m to 10 to 30 m below ground in a downslope direction. There is a

wide range in particle size between materials in different areas. Very

large boulders or corestones could exist at high levels of the ground.

Metallic objects, anchors and cannons may also be expected in the old

filling areas and in marine deposits.

Groundwater levels tend to be high, generally 2.5 to 3.5 m below ground

level, and tidal response affects much of the urban area.

Shaft Construction

In urban areas, due to constraints of traffic and existing utilities, some of

the jacking and receiving shafts have to be constructed at side streets.They are generally constructed by sheet-piles in homogeneous clayey

to sandy ground (Fig 1) and pipe-piles in mixed ground conditions

(Fig 2). Vibration and settlement monitoring are carried out during the

piling operation to avoid causing damage to adjacent utilities, services,

roads and structures. More expensive pipe-piles are sometimes used in

hard ground to minimise noise and vibration. For sheet-piles, to minimise

vibration, boulder obstructions at intermediate depths are pre-bored

before commencement of pile driving. At some locations, due to the

presence of hard materials at different depths, it would be difficult to

maintain the verticality of the sheet-piles during driving, and the toe

of the sheet-piles would easily be damaged, causing the problem of

interlocking with adjacent piles, often with insufficient embedment length,

and necessitating toe grouting as a remedial measure.

Rectangular shaft is usually constructed because it is more easily to

be modified to accommodate existing utilities and services. However,

at locations where these features are absent, circular shaft is used due

to the smaller member size of temporary works required. For a 1,800

mm diameter TBM, the typical size of a shaft is generally 8 m x 8 m

or 8 m in diameter. This generally would necessitate the occupation of

more than two traffic lanes. As such, the construction has to be carried

out in stages, with one portion completed and decked-over before the

commencement of another, such that disruption to traffic could be

minimised. At traffic sensitive locations, the receiving shaft could be

temporarily decked over after construction and re-opened to allow traffic

flow until the pipejacking drive is completed and the TBM can be lifted

up to ground surface during traffic non-peak hours.In areas of congested utilities and services, it is usually difficult, if not

impossible, to have a clear shaft, by virtue of the long time required

for utilities diversion and the limited space. Therefore, unless they

obstruct the pipejacking operation such as lowering of TBM/jacking

pipes or removal of excavated material, these utilities and services are

temporarily supported inside the shaft, by steel frames. This, however,

would create windows in the temporary works, entailing the erection of

steel lagging plates as support and to prevent ingress of groundwater

(Fig 3). Sometimes, the shape and size of a shaft need to be tailor-made

to suit utility constraint, resulting in the use of a combination of sheetpiles

and pipe-piles to overcome the problem. In some cases, raking piles

Figure 2 Temporary Shaft Formed by Pipe-piles

Figure 1 Temporary Shaft Formed by Sheet-piles

Figure 3 Steel Lagging Plates Provided in the Window of TemporaryWorks

have to be constructed to avoid interference with existing utilities and

services. The use of a concrete wall cast against the pipe-piles is always

required to ensure the stability of the shaft if watermains or drainage

pipelines are in their close proximity as their bursting/breakage could

significantly disturb the ground.

For deep shaft, grouting is always required in the perimeter to ensure

watertightness, before excavation is to commence. After the shaft has been

formed, a thrust wall and a launching/receiving eye are then constructed

to allow the pipejacking operation. For multi-direction driving, a circularthrust wall can provide better orientation and transfer of loading.

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2 bars is required to balance the water head in the excavation face and

be maintained inside the tunnel round the clock to avoid flooding which

may in turn affect tunnel stability. To ensure constant supply of air, a

standby compressor is provided for emergency situations. Pressurisation

and depressurisation is required in the air-lock installed on top of an air

deck erected in the jacking shaft, for personnel entering and leaving the

tunnel respectively. A medical lock needs to be provided at the shaft

location when the applied compressed-air pressure exceeds 1 bar. There

have been some cases that air was found leaking through the porous

ground during tunnel excavation, resulting in inflow of groundwater. This

entailed horizontal grouting from inside the handshield to stabilise theground before further excavation could be proceeded with.

The rate of excavation is generally 1 - 2 m per day for free-air tunnel

and 0.5 - 1 m per day for compressed-air tunnel, depending on the

ground conditions.

Heading Construction

Heading construction is a simple form of hand-dug tunnel, and is widely

used to construct short pipelines, usually in the range of 10 - 30 m

in length, crossing road junctions or locations of congested existing

utilities and services, in shallow depth, due to its easy setup and thus

the relatively low cost. The tunnel size could generally vary from 1.5

to 2.5 m in diameter, depending on the size of pipeline to be installed.

To tackle different site constraints and ground conditions, the methodof construction in each tunnel could vary, and the following cases are

typical examples.

To suit the limited space in the jacking shaft which is a common

phenomenon in urban areas as constrained by existing utilities, the shield

head can be tailor-made by several short sections and connected together

Depending on the size and depth of the shaft, and the ground conditions

encountered, each shallow shaft (less than 8 m in depth) generally

requires 6 to 8 weeks for completion from piling to excavation. The

construction for deep shaft (up to a depth of 22 m) would however take

a longer time, from 12 to 18 weeks, due to the high variation in ground

conditions, particularly the rock content.

These shafts are later used for construction of permanent shafts for future

maintenance. As most of the shaft locations have different degree of

utility constraints, the location, size and shape of access and desilting

openings of each permanent shaft may need to be tailor-made to suit

the site condition.

Modes of Tunnelling Operations

Three modes of operations are commonly adopted for pipejacking

works in Hong Kong. They are hand-dug tunnel, earth pressure balance

TBM and slurry pressure balance TBM. The contractor will, based on

the results of site investigation conducted in the design stage by the

client, assess the risk and carry out further investigation if doubt exists

and select the most appropriate mode for the ground conditions likely

to be encountered.

Hand-dug Tunnel

Hand-dug tunnel, formed by precast reinforced concrete segments astemporary lining and connected each other with a bolting system and a

rubber gasket at the joint to prevent ingress of water, can be constructed

under either a free-air or a compressed-air environment.

Free-air tunnel (Figs 4 and 5) is suitable for shallow pipelines crossing old

seawalls, artificial obstructions and road junctions, usually less than 50 m

in length for a drive. Prior to tunnelling, the alignment of the pipeline is

fully stabilised by grouting to ensure stability. The excavation is effected

manually by pneumatic tools or mechanically by a mini backhoe inside

the handshield (ie a protective tube in front of the pipeline to allow

manual excavation by workers), if the diameter of the tunnel permits

(usually 1,800 mm or above). The excavated materials are transported

to the jacking shaft by a trolley system and then lifted up to ground

surface. The handshield is advanced by extending the hydraulic jacks

installed with it, against the concrete segments erected at the rear as

reaction. New segments are then added after the retraction of hydraulic

jacks. The overcut between the ground and the segments is immediately

filled up with grout to prevent settlement. This procedure is repeated until

the tunnel reaches the receiving shaft. Upon completion of the tunnel

construction, a permanent pipeline is pushed inside from the jacking

shaft and its annulus is filled up with grouting materials equivalent to

the strength of the overlying ground.

Compressed-air tunnel (Figs 6 to 8) is applicable to grounds where

groundwater table is high. Depending on depth, an air pressure of 1 to

Figure 4 Launching of Hand Shield for Free Air Hand-dug Tunnel

Figure 5 Excavation in Free Air Hand-dug Tunnel

Figure 6 General View of Compressed Air Setup in Jacking Shaft


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one by one by welding inside the jacking shaft before launching. This

is then followed by steel sleeve pipes or precast concrete pipes which

are pushed forward into ground by a hydraulic system in the jacking

shaft (Fig 9), with lubricant constantly injected under a pressure slightly

higher than the overburden pressure, from the grout holes installed in

the pipes to minimise soil friction, and to avoid close-up of the overcut,

causing ground settlement, during the jacking operation.

To determine the ground condition, probing is carried out in every

2 - 3 m ahead of excavation. The ingress of water, if any, is controlled

by the injection of grout, by means of horizontal and inclined holes

from the shield head, prior to excavation. If instability is found in the

working face, steel shutter, in the form of plankings, needs to be erected

at the front of the shield (Fig 10), and the working personnel evacuated

until the ground treatment is completed, by specialised working gangs,

After pushing the sleeve pipeline into the receiving shaft, the annulus,

formed by overcut, is filled up with grout, with a strength equivalent to

the overburden pressure, to avoid ground settlement.

At narrow shaft locations where lowering the sleeve pipes is a problem,

the tunnel lining could be formed by steel segments connected to each

other by welding (Fig 11).

The advancement of the shield head is effected by extending the hydraulic

jacks installed with it against the steel segments erected at its rear

(Fig 12). The overcut outside the segments is immediately filled up by

grout, through the holes provided at the crown and the axis at the twosides, after the completion of each ring in the tunnel. This method is

generally applicable to the construction of small size of pipelines.

For crossing major roads where underground boulder obstructions are

expected, the temporary works in the tunnel, formed by drilling horizontal

pipe-piles from one shaft to another, could effectively penetrate through

such obstructions to act as temporary lining (Fig 13), thus ensuring the

stability during excavation. Depending on ground and groundwater

Figure 7 Excavation in Compressed Air Hand-dug Tunnel

Figure 9 Jacking of Steel Sleeve Pipe for Heading Construction

Figure 8 General View of a Completed Tunnel

Figure 11 Appearance of a Tunnel Formed by Steel Segments

Figure 10 Steel Planking Erected in Excavation Face to Prevent Ingressof Groundwater


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conditions, grouting may be required to stabilise the ground by injection,

through the slot holes provided in the pipe-piles, before excavation

takes places. The permanent pipeline is then pushed into the tunnel

after excavation (Fig 14), and its annulus is filled up with lean concrete

or grouting materials, as appropriate. This method is usually suitable for

constructing relatively large size of pipeline in deeper ground.

For tunnelling in filling ground with low rock content in shallow depth,

the temporary works could be in the form of a portal frame, constructed

by driving several short sections of steel plankings or channels, in the

direction of excavation, ahead of excavation, and then supporting them

by steel members after excavation (Fig 15). This method is howeverunsuitable for water bearing ground due to the presence of gaps between

the plankings/channels that the ingress of water could pose stability

problem in the tunnel, particularly during dewatering.

The average production rate for heading construction is generally

1 - 2 m per day. If large boulders or full-face rock are encountered in the

excavation face, their removal has to be carried out by pneumatic tools

as the size of the tunnel does not allow the use of heavy mechanical

plant. Hence, the rate of progress is generally slow, with 100 - 200 mm

in length achieved per day. In addition, maintaining stability of overlying

ground during boulder removal is always a problem.

The heading construction method also enables the alignment of a

tunnel to be adjusted, by lowering or shifting the shield head/segments

to either side, to avoid conflicting with unexpected utilities or services

encountered during excavation, thus giving more flexibility to resolvingthe problem, when compared with the TBM tunnelling.

Heading construction, by means of steel plankings and portal frames,

has become popular in Hong Kong recently, particularly for installing

branch sewers or drains where groundwater is usually not a problem.

This is due to its easy setup, not requiring heavy machinery, and its

flexibility in handling obstructions. The downside of this method is that

construction may be dangerous if the soil cover is too shallow. Its left-

in temporary works also takes up an underground space, filled with

steel sections, much larger than the pipes to be laid, typically 1.5 m x

1.5 m, to enable manual operation, thereby making the already congested

underground space even more so and also imposing difficulties for future

maintenance of the laid pipes.

Earth Pressure Balance Method

Earth pressure balance TBM (Figs 16 to 18) is adopted for tunnelling

through homogeneous ground made of clay, silt or sand, usually in the

layers of fill, marine deposits and alluvium. The cutting wheel generally

appears in spoke type, with tungsten carbide cutting bits mounted on

the surface and a screw crusher in the centre. It is capable of excavating

soft rocks of sizes up to 25% of the area of the cutting wheel.

The system works on the principle of maintaining pressure in the

excavation chamber equal to the hydrostatic pressure in surrounding

ground. This pressure is constantly monitored and controlled by varying

the speed of the screw conveyor. The excavated materials are transported

to the jacking shaft, by a trolley system, and then lifted up to ground

surface. When soft ground is encountered or excavation is carried out

Figure 13 Tunnel Formed by Horizontal Pipe-piles Figure 15 Hand-dug Tunnel Constructed by Steel Plankings with PortalFrames

Figure 12 Extension of Hydraulic Jacks in Lead Pipe for Advancement Figure 14 Permanent Pipeline Installed in the Tunnel


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below groundwater, high water absorbent polymer or other conditioning

agents are added to the excavation chamber firmly grabbing the soil to

stabilise the excavation face and to ease the mucking process.

For jacking shaft, the works area required is less than that of the slurrypressure balance method, due to less plant required for the operation,

and could vary from 3.5 to 5 m in width (ie the width of the shaft) and

be generally in the range of 20 - 30 m in length. At locations where

space is a problem, the size of the works area could be reduced by

stacking some of the plant. For receiving shaft, the works area is much

smaller and is only required when the TBM is lifted up from the shaft

after completion of the pipejacking works.

Common sizes of TBMs range from 1,050 mm to 1,800 mm, but the

use of 2,600 mm diameter TBMs has been experienced. Due to their

simple configuration, in particular only cutting bits are equipped in the

cutting wheel and no telescopic section is provided at the rear of the

TBM, these TBMs cannot cut through big boulder obstructions and are

therefore generally suitable for soft ground excavation. Manual removal

of artificial obstructions ahead of excavation or change of damaged

cutting tools cannot be done from behind the cutting wheel in most

of TBMs due to no man access in the front bulkhead. To account for

unexpected ground conditions, the length of each drive is usually less

than 100 m.

A production rate of 6 - 8 m per day could be achieved in filling ground

with occasional boulders.

There is another type of TBM using this operating mode but has different

configuration in the cutterhead and thus the cutting tools (Fig 19).

Consisted of two main parts in the TBM and built of heavy gauge steel,

the front bulkhead of the first part acts as support for the boring unit

and seals the front chamber for pressurisation. This part of the TBM,called the shield, houses the machine operators porthole, a spoil screw

conveyor and an access chamber to the face of the TBM for manual

excavation under a compressed-air working environment. The second

part is the telescopic tailskin which can extend to provide sufficient

thrust to the shield and is also used for connecting the precast concrete

pipes/segments behind. An articulated joint is provided between the

shield and the tailskin, to enable steering of the shield so that the line

and level of the pipeline can be adjusted.

In normal operation, this type of TBM is operated in closed mode, and

excavation is effected by a boom cutter or a mini-backhoe connected

to an articulated telescopic arm mounted on a fully rotating turret in

clockwise or anti-clockwise direction, and the mucking chamber is under

compressed-air to balance groundwater. In this mode, transportation

of the excavated materials is similar to that of the TBM with a cuttingwheel. In order to prevent loss of compressed-air, the excavated materials

in the screw conveyor are always kept full. When the TBM is operated

in open mode for removing obstructions manually, the triangular steel

panels hinged to the leading edge of the shield, which act as shutters,

are extended by hydraulic jacks operated from the drivers cabin, to

support the overlying ground during the operation.

There has been a case that the TBM was stuck in ground in the middle

of a drive, due to the accidental opening of a valve in the front bulkhead

which resulted in the ingress of soil and water in the TBM, causing

inundation and damage. This TBM was finally recovered by a rescue

tunnel constructed from the receiving shaft, and the stalled pipeline was

then pushed to the receiving shaft through the rescue tunnel.

Slurry Pressure Balance Method

Slurry pressure balance TBM (Figs 20 to 22), often called slurry shield, with

cutting bits and disc cutters installed at suitable locations in the cutting

wheel, of semi-dome type or dome type, is widely used to construct

pipelines in mixed to hard ground conditions under groundwater, to a

depth up to 30 m. Common sizes of TBMs are 1,200 mm, 1,500 mm

and 1,800 mm.

The allowable jacking load in these TBMs ranges from 500 to 1000

tonnes(T), whereas the allowable torque pressure is in the range of

100 - 300 bar. The length of driving could vary from less than 50 -

100 m to more than 500 m passing through a number of intermediate

shafts in a single drive.

The works area required for jacking shaft is generally 7 - 8 m wide and40 - 50 m long, for placing mobile crane, TBM control container, power

Figure 18 Transportation of Excavated Material in Jacked Pipeline

Figure 16 Typical Pipejacking Works Using Earth Pressure Balance TBM(Courtesy of Herrenknecht AG)

Figure 17 Mechanism of Earth Pressure Balance Method (Courtesy ofHerrenknecht AG)


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Figure 19 Operation of an EPB TBM Using Mini-backhoe for Excavation (Courtesy of CSM BESSAC)

Figure 20 Typical Pipejacking Works Using Slurry Pressure Balance TBM(Courtesy of Herrenknecht AG)

Figure 21 Mechanism of Slurry Pressure Balance Method (Courtesy ofHerrenknecht AG)

Figure 22 General View inside a Jacked Pipeline Installed by SlurryPressure Balance Method

pack, generator, desander, muck tank, bentonite mixer, grab lorry, and

jacking pipes, etc. At certain locations, some equipment have to be put

on decks to suit the limited size of the works area as constrained by site

conditions, or a satellite works area has to be provided in the vicinity.

TBMs of 900 mm in diameter or smaller may be incapable of tunnellingthrough big rocks due to the size of the cutting wheel limiting the

number and size of the disc cutters. Therefore, advanced drilling to

determine the ground conditions along the pipeline alignment needs to

be carried out prior to commencement of the work to minimise the risk

of TBM stoppage and thus the rescue operation. There has been a case

that a 600 mm diameter TBM encountered full-face rock after leaving

the jacking shaft for about 1 m (Fig 23) and was stuck. The TBM was

finally pulled back to the shaft and the rock obstruction was removed

by percussive drilling prior to resumption of tunnelling.

During the course of driving, bentonite based slurry, with a viscosity

of 40 - 50 Marsh sec for sandy ground, is constantly pumped into the

excavation chamber, through a slurry charge pipe. This forms a cake

over the excavation surface, to stabilise the face and prevent the ingress

of groundwater. The mix of slurry needs to be adjusted to suit thematerial in the excavation face. Sometimes, polymer has to be added to


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slurry to increase the performance in adverse ground conditions, by, for

instance, decreasing the ground porosity or improving the properties of

the excavated materials in soft ground to maintain the ground stabilityduring excavation. The excavated materials are then pumped to ground

surface and then separated by a desander, with the slurry being recycled

for use and the spoil disposed of off site. For clayey ground, no slurry

is used and water under pressure is injected for the intended purpose.

Lubricant is also injected to the overcut along the pipeline, through

the lifting holes at the crown of the jacking pipes and the holes in

their axis, by an automatic system with pre-set timer and volume of

flow (Fig 24). Intermediate jacking stations, each with 8 - 12 nos 50 -

80 T hydraulic cylinders, are installed at pre-determined locations of the

pipeline, usually every 80 - 100 m, to avoid excessive loading in the

main jacking station. However, no intermediate jacking station can be

installed in pipelines of 600 mm in diameter or smaller due to limited

space. In addition, jacking pipes of such sizes do not have the holes

for injection of lubricant. Therefore, the jacking is generally limited toshort length, say 30 - 40 m.

For rock excavation, disc cutters, each with single or double discs, with

a diameter range of 200 - 300 mm, are equipped in the cutting wheel

and each disc cutter exerts a thrust of 20 - 30 T onto the rock face,

forming vertical and radial cracks in circular kerbs at distances of 60

- 100 mm. By repeated rotations of the cutting wheel and disc cutters,

these cracks are enlarged and eventually cause the rock mass in between

to be broken into small fragments. The fragments are further reduced in

size by the conical crusher at the rear of the cutting wheel, to a size of

not more than 40 mm in diameter. In view of travelling a longer path

for excavation due to their positions, gauge disc cutters (ie near the edge

of the TBM) usually require more frequent replacement than centre disc

cutters (ie near the centre of the TBM).

For TBMs with a diameter of 1,500 mm or larger, a horizontal air-lock is

generally provided at the rear for enabling inspection of the condition of

disc cutters and making necessary replacement, through the man access

in the front bulkhead, under compressed-air. For tunnelling through hard

ground, a telescopic section is equipped in the TBM or an intermediate

jacking station is provided behind the TBM, to provide sufficient thrust

for excavation.

The advancement rate of TBM is 100 - 200 mm/min in soft ground

to 20 - 30 mm/min in hard ground. The TBM daily production rate

depends on the configuration of the TBM and could vary significantly

under different ground conditions.

Based on DSD Contract No DC/2000/11 [5], 2 m per day in hard

ground to 30 m per day in soft ground, with an average of 4.5 m per

day, could be achieved. A set of disc cutters is capable of completing

2 shallow drives and 1.5 deep drives respectively, under typical HongKong soil conditions.

In some cases, the pipeline has to pass through existing reinforced concrete

seawalls, requiring the affected portion to be completed by hand-dug

tunnel before the use of TBM to complete the remaining drive.

Ground Settlement

Tunnelling and pipejacking would induce settlement in surrounding

ground. The magnitude of settlement is greatly affected by ground

conditions, type of tunnelling method, depth of tunnel and jacking

speed. The presence of underground utilities and services above the

jacked pipeline would lead to under-measurement of surface ground

settlement due to their rigidity. It is necessary to estimate the settlement

influence zone and to assess its effect on nearby roads, structuresand utility installations such that they can be safeguarded during the

operation and remedial measures taken, if necessary. Maximum ground

settlement occurs at the centre line of the pipeline and diminishes to

zero at a distance from its two sides.

Figure 23 View of Full-face Rock outside the Launching Eye of JackingShaft

Figure 24 Conditioning and Lubrication for Jacked Pipeline


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The majority of ground settlement (70 - 80%) occur during and immediately

after completion of tunnelling and pipejacking works. Further settlement

would continue, and its stoppage depends on the ground conditions

above the jacked pipeline, for a few weeks to a few months.

Dated back to 15 - 20 years ago, the settlement was monitored using nails

installed on pavement. However, this type of installation is unable to detect

settlement accurately below rigid concrete pavement. In a project, a road

collapsed due to the presence of cavities in ground without indication by

the monitoring data. After this incident, sub-surface settlement markers, in

the form of a steel rod, by coring through rig id pavement, are generally

adopted, with their installation at suitable intervals along the alignment

of the pipeline and at offset at both sides, prior to commencement of

a pipejacking drive. In flexible pavement, nail markers are used. This is

supplemented by visual inspection that if settlement occurs, cracks would

develop in pavement. For structures sitting on shallow foundation, their

condition has to be assessed before commencement of tunnelling and

pipejacking such that suitable monitoring devices such as tilt markers

and settlement markers can be installed to monitor the ground behavior

during the course of works.

Under normal situations, the monitoring is carried out once a day. This

frequency however may have to increase if there are abnormal readings

or the magnitude of readings changes abruptly. In the event that if the

measured ground settlement exceeds the predicted value, the tunnelling

and pipejacking works have to stop and an investigation on the cause, andthe damage, if any, carried out, with remedial measures such as ground

treatment implemented, as necessary, prior to resumption of work.

Through the proper operation of works, the ground settlement for most

of the pipejacking drives using TBMs could generally be controlled

within 15 mm for most of the Hong Kong soils, although excessive

ground settlement has been noticed in some drives due to unfavorable

ground conditions.

Control of Tunnel Alignment

The pipejacking works in Hong Kong using TBMs generally follow the

Tunnelling Specification [6] as guideline for controlling tunnel alignment,

in that a tolerance of 50 mm and 35 mm is specified for line and level

respectively. For the 4 km long pipejacking drives completed in DSD

Contract No DC/2000/11, under different ground conditions, 21% for

line and 19% for level exceeded the tolerance, generally by 2 - 50 mm,

despite the fact that the excavation face had been conditioned by slurry

and sometimes by the addition of polymer, as necessary. Moreover,

deviations in more than 100 mm were recorded at some locations in a

few drives where the ground conditions were alternating. In addition,

about 2% of the pipelines exceeded the tolerated 0.5 degree angular

deflection at pipe joint, resulting in the need to carry out a detailed

inspection to ensure that there is no dislocation thereat. For excessive

opening in pipe joint, remedial measures have to be carried out. This

could be achieved by locally trimming the concrete at the pipe end for

better bonding before applying nor-shrinkage epoxy, with a strength

equivalent to the pipe, to fill up the problematic location for prevention

of ingress of water.

The tunnel alignment is corrected by suitable extension or retraction of

the steering cylinders installed in the TBM. A TBM with 4 nos steering

cylinders has better control in alignment than that with 3 nos Out-of-

tolerance in alignment requires a long length to correct in order to avoid

causing damage to the jacking pipes.

For pipejacking works using handshield for excavation and sleeve pipes/

segments to construct the temporary tunnel, no tolerance is specified

for line and level as the tunnel will be large enough for installation of

the permanent pipeline. However, allowance has to be made to account

for the irregular profile of the tunnel, due to encountering different

ground conditions during excavation, which could affect installation of

the permanent pipeline therein to the required alignment.

For the tunnel formed by horizontal pipe-piles or steel plankings/channels, its alignment may need to be adjusted to cater for unexpected

obstructions due to existing utilities and structures. In the worst case,

the design of the permanent pipeline has to be modified to suit the

actual site condition.

Rescue Operations

A TBM would be stuck in ground if obstructions are encountered during

excavation. It is necessary to carry out a detailed investigation on its

cause, and then replacement of the damaged part from inside the TBM.

These obstructions could be natural or artificial. If the problem cannot

be overcome, the stalled TBM has to be recovered by means of a rescueshaft or a rescue tunnel, as appropriate, with the obstruction removed.

The works would be delayed and new TBMs may need to be deployed

for ensuring the completion of other pipejacking drives on time, which

could disturb the programme of works.

Based on DSDs Report No RD 1005/2 [3], about 2% of the pipejacking

works encountered obstructions, resulting in rescue operation.

The selection of a rescue option depends on many factors such as

the damage in the TBM, the location of TBM stoppage with regard to

its distance from the jacking shaft and the receiving shaft, the traffic

conditions, and the ground and groundwater conditions, above the

TBM, the constraints of utilities and services, and the effects on nearby

structures and facilities. The options may include but are not limited to

change of the damaged cutting wheel so that the TBM can continue

the remaining drive to the receiving shaft, removal of the TBM through

the rescue shaft and completion of the remaining drive by another

TBM from the receiving shaft to the rescue shaft, and construction

of a rescue tunnel from the receiving shaft, to overlap the TBM and

then the pipeline is pushed into the receiving shaft from the jacking

shaft. As each option involves different degree of risk, its suitability

needs to be assessed carefully, with site investigation works carried

out at and in the vicinity of the stalled TBM, before a decision is

made.

There have been two cases that a rescue shaft, formed by a combination

of sheet-piles and pipe-piles, in the size of 1.8 m x 5.2 m on top and

2.5 m x 5.2 m at bottom and 16.5 m deep, and a rescue tunnel, with a

length of 35 m and an internal diameter of 2,440 mm, using compressed-

air pressure to balance groundwater, took about 8 months and 10months respectively for rescuing the stalled TBM, from investigation on

the cause of the problem, planning of rescue, construction, execution,

to recovery of the TBM [7].

There has however been a case that a 1,350 mm diameter slurry

operated TBM encountered a steel box section when tunnelling in river

bed and could not advance further. The cutterhead of the TBM was

moved backward by retraction of the steering cylinders, to enable the

driving, vertically, of a 900 mm diameter steel pipe for encasing the steel

section. An attempt to completely lift up this steel section through this

steel pipe was carried out but breakage occurred at the location partly

cut by the disc cutters of the TBM, during the lifting operation. To enable

man-entry for manual removal of the steel section, a steel plate, with a

prefabricated hole to accommodate the steel section, was installed in the

casing, with sandbags added on top of the plate to prevent uplift forcedue to water pressure, and the ingress of water in the steel casing was

controlled by the use of a pump. The broken steel section was finally

cut manually and removed, and the pipejacking works resumed.

Some Problems Encountered

The following problems are commonly encountered during pipejacking

works and could affect the progress:

For deep drive, high groundwater pressure requires additional jacking force

to advance the TBM against the pressure. Therefore, more intermediate

jacking stations have to be installed at suitable intervals of the pipeline

to ensure that there is sufficient thrust to push the pipeline forward. In

addition, such high groundwater pressure also makes the TBM and the

first few pipes moved back to the jacking shaft whilst new pipes arebeing added. This always requires the temporary fixing of a steel bracket


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in the TBM/pipe to rigidly connect to the surrounding temporary works

as support during pipe connection.

A treated soil block, formed by grouting, is usually provided in the ground

outside the launching eye of the jacking shaft and the receiving eye of the

receiving shaft, to prevent ingress of water during the jacking/receiving

operation and to support the TBM during launching and reception. In

grounds with high content of boulders, the grout may not be able to

provide effective bonding between soil and rock. This would easily

cause dispersion in the grout block when the TBM is breaking through.

As a result, soil particles would migrate into the shaft, through the eye

location, and settlement would occur in overlying ground, damaging

utilities and services.

During the course of pipejacking, zig-zag line and level would occur

in the pipeline due to encountering different ground conditions. This

would require rendering in the depressed sections to provide a uniform

profile for the pipeline, affecting hydraulic performance. Excessive out-

of-tolerance would also cause opening-up of pipe joints, causing ingress

of groundwater and instability of the pipeline.

Cracking of concrete in pipe could happen at locations where there is

excessive deviation in line and level caused by uneven distribution of

jacking force, as a result of unfavourable ground conditions encountered.

This would require a temporary steel lining for protection to complete

the remaining drive before repair is carried out. In the worst case, the

damaged pipe has to be repaired immediately, with the spalled ordefective concrete removed and replaced by high strength non-shrinkage

epoxy, before the pipejacking works can continue.

When tunnelling through clayey ground, slow transportation rates in

the slurry discharge pipe always occurs, due to the plastic material

accumulated in the inlet of the spoil disposal chamber. This necessitates

high pressure water to disperse such material through the nozzles provided

nearby. Pipe blockage is also found when obstructions such as timber,

steel bars, etc are encountered, resulting in the long time to dismantle

the respective sections of pipes for clearance.

Wear or damage in disc cutters is a normal phenomenon in TBM

during tunnelling, and replacement has to be made at the right time to

ensure their proper function. There are however cases that they could

not be replaced from inside the TBM due to damage/distortion of theirconnections, affecting the cutting capacity and losing the function of

further advancement.

Excessive ground settlement or subsidence would occur in unstable

ground or due to improper control of the TBM, causing bursting of

watermains or gas mains. Although settlement monitoring is carried out

at regular intervals, this situation would still occur when there is a sudden

change in ground conditions not immediately noticeable to the

TBM operator for necessary adjustment in the TBM. Excavation in

bouldery ground or soft ground with boulders would also have such a

phenomenon.

Repeated extension and retraction of hydraulic jacks would cause

intermediate jacking stations to leak, due to the rubber seal being torn

out by such operation. This situation would be more critical in curved

alignments under eccentric loading throughout the drive. No repair couldbe made until completion of the drive. If the leaked location is near the

TBM, the tunnelling operation might be jeopardised.

In porous ground, slurry injected from the TBM to balance groundwater

pressure would easily leak into ground, cause blockage to ductings of

utilities, and encroach into drainage features, affecting their function.

The tunnel alignment is affected by ground conditions during driving. It

would be difficult to control the alignment in soft ground with boulder

embedment or in alternating ground with soft and hard materials as the

TBM would tend to move faster towards soft materials. The hydraulic

performance of a pipeline would be affected should there be excessive

deviation in alignment.

A TBM would be stuck in ground if it cannot cut through obstruction

during the course of driving. This would result in the rescue operation,

and high frictional force would develop along the pipeline due to close-

up of the annulus, causing difficulty to further proceed with pipejacking

works.

Discussion

Appropriate Selection of Method to Avoid Delays

According to DSD Report No RD1005/2 [3], about 75% of the pipejacking

works were completed by TBMs using the slurry pressure balance method,

1% by the earth pressure balance method and 24% by hand-dug tunnels.

However, there is a rapid increase in the use of hand-dug tunnels, in

the form of heading construction, in recent years.

Each of the pipejacking techniques is beneficial when used in a proper

manner. Its performance is generally reflected by daily production rate,

capacity in dealing with hard rock, control of line and level of pipeline,

and ground settlement or heaving. It is therefore essential to choose the

appropriate method to avoid timely and costly remedial measures if the

work is stopped by obstructions or mechanical failure, which will cause

nuisance to the public and in turn lose the spirit of using them.

Cost of Installation and Choice of Techniques

The cost of pipeline installation using such techniques does not vary

with depth except for the increased cost of providing deeper shafts and

manholes. In comparison with the conventional open-trench method, the

cost of the slurry pressure balance method, the earth pressure balancemethod, the free air hand-dug tunnelling method with grouting and the

compressed air hand-dug tunnelling method is higher in the order of 2 - 10

times, whereas the construction time is usually faster in most cases.

The choice of a technique lies with the designer or the contractor and is

dependent on the degree of risk that the project can accept. This is usually

governed by access, ground and groundwater conditions and accurate

identification and consideration of all other constraints. Increase in site

investigation works would reduce the risk but could not eliminate it.

The earth pressure balance method, although relatively inexpensive of

tunnelling in soft ground, is unable to deal with large boulders and artificial

obstructions. Although access to the face through the airlock chamber

in large TBMs is feasible, their removal will be inefficient due to limited

space and the use of only hand tools. Breaking through the unknownthickness of boulders will pose a risk that there may be a sudden change

in groundwater pressure endangering the worker. Therefore, the recent

trend is that slurry operated TBMs have been used as a substitute to

minimise the risk of TBM stoppage due to the above problems.

The slurry pressure balance method has demonstrated its good rate of

progress in variable ground, but its use needs monitoring of excavation as

the machine advances to eliminate settlement (too much excavation, not

enough advance) or heave (too much advance, not enough excavation).

Hence, the operators experience, training and response when problem

arises are crucial. Change of operator during the course of work should

be avoided as much as possible as the new operator would take a long

time before he becomes familiar with the TBM and the ground conditions.

The density, viscosity, filtrate water and shear strength of the slurry have

to be tested on a regular basis and changed when any of these exceedsthe specified upper or lower bound limits to ensure its functionality. The

configuration in the cutting wheel should be capable of cutting through

extremely hard and abrasive rock and, on the other hand, excavating

soil efficiently. The disc cutters provided have to be extremely wear

resistant and capable of taking the maximum thrust of the TBMs. To

avoid excessive heat generation, disc cutters should be equipped with

water cooling system. Locally made discs are to be used with care due

to difficulty of controlling their quality during the heat treated process.

In the event that a boulder zone is identified ahead of the drive, it may

be necessary to stabilise the soil above the affected area to minimise

ground settlement caused by vibration or over-excavation during the

cutting-through operation. This would also help to control the line and

level of a pipeline. It may be worthwhile to note that up to now, no

TBM is capable of cutting through large artificial obstructions, especiallymetallic objects, resulting in its stoppage in ground.


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Problems with TBMs

The type of cutting wheel and TBM to be used and the expected advance

rate depends on ground conditions and their variability likely encountered.

A radical and unexpected change of ground conditions can prevent a

drive from being completed and require rescue operation to permit the

work to be completed. Likelihood of obstructions, natural or artificial, can

also prevent a drive from being completed, and the rescue of a stalled

TBM could be time-consuming and expensive, affecting progress.

Additional Features in New TBMs

Research in TBM technology has developed rapidly in recent years,

based on the problems encountered in different projects under different

ground conditions. New TBMs are now equipped with additional features

that allow increased and reliable performance under a range of ground

conditions. To account for the high variability in ground conditions in a

short length, which is a main characteristic in Hong Kong soils, mixed

ground slurry operated TBMs have been widely adopted by contractors

to minimise the risk.

Advantages of Lubricant

Lubricant, applied along the jacked pipelines, has demonstrated to be

effective in lowering jacking forces and reducing the risk of pipe damage

in most of the pipejacking drives. In long drives, automatic bentonite

systems with programmable valves should be used to ensure that lubricant,with the specified volume, is injected to the annulus of the pipeline in

pre-fixed intervals, to serve the intended purpose.

Laser Guidance System

In straight drives, the position of TBM is determined by the guidance

system which relies on the laser beam transmitted from the laser device

installed at the rear of the jacking shaft, to the target plate installed in

the TBM. However, in curved drives, the laser technology with the use

of reference prisms and total survey stations is generally used in TBMs

with diameters of 1,800 mm and larger. In small TBMs, the use of Gyro

compasses with hydrostatic grade correction is a common approach and

has demonstrated its accuracy.

Problems with Disc Cutters

The performance of disc cutters for pipejacking works has a short history

in Hong Kong. In 1990s, most of the works were carried out in single

drives, with a length generally not exceeding 100 m, and in shallow

depth. It was until 1996 onwards that the scale of pipejacking works

has increased to a few kilometres in a contract, with also deep drives

tunnelling through hard strata in ground. However, no complete record

on the respective performance could be traced except in DSD Contract

No DC/2000/11. This Contract showed that a total of 254 nos steel alloy

disc cutters, with a diameter range of 250 - 300 mm, had been used

for the 21 drives, averaging about 0.5 set of cutters for each shallow

drive and 1.5 sets for each deep drive. For TBMs with a diameter of

600 mm to 1,800 mm, a set of disc cutters in the cutting wheel has

6 - 12 nos. Depending on the ground conditions encountered, particularly

the location, thickness and hardness of materials, some of the disc

cutters had to be replaced after the TBM had travelled a short length.

This situation occurred in some long, curved drives with highly variable

ground conditions and the replacement of disc cutters in a 4 m drive

length had been experienced in the worst case. Replacement of more

than 30 nos disc cutters during the course of works in three drives had

been recorded. It is noted that a tunnel through moderately to slightly

decomposed granitic (M/SDG) bedrock, with strengths of 320 - 350

MPa, achieved 4 m/day on average.

Tunnel Alignment and Level Accuracy

Almost all the tunnel alignments, using TBMs, can be controlled within

75 mm for line and 50 mm for level, as evidenced by DSDs three

contracts (Nos DC/95/05, DC/98/06 and DC/2000/11) which specifiedthe use of tunnelling and pipejacking techniques. In consideration of

the steering capacity of the TBMs available in the market, the angular

deflection of the jacking pipes, and the procedure of correcting the out-of-

tolerance, a tolerance of 50 mm for line and 35 mm for level, as stated

in the Tunnel Specification, may not be applicable to all Hong Kong soils

for pipejacking works, and hence should only be used with care.

Hand-dug Tunnels and Heading Method

The adoption of compressed air hand-dug tunnelling method would

face a problem associated with air loss in porous ground, giving rise to

the necessity of carrying out ground treatment to safeguard the tunnel

and the personnel working inside. The switch on of compressors and

generators around the clock to maintain the pressure in tunnel also

causes noise problem. Although high cost and relative low production

rate make this method only applicable to short drives, the removal of

artificial obstructions can be warranted. However, after a few drives had

been completed under DSD Contract No DC/95/05, and following the

rapid development of TBM technology which allows pipejacking drives in

curved alignment and detects obstruction ahead of TBM advancement,

this method has not been used in recent years due to the risk involved

and the reasons stated above.

Free air hand-dug tunnelling method in unstable ground would require

the entire length of the drive being grouted to maintain stability of the

road above, prior to commencement of work. Vertical grouting appears

to be infeasible due to presence of congested utilities and services inshallow depths. Horizontal grouting will cause drawdown of groundwater

during the drilling operation and will blow out the ground or encroach

into ductings of utilities if the pressure is not properly controlled. If the

grouting is ineffective, compressed air still has to be used to balance

groundwater pressure.

Heading construction is a method commonly adopted to construct

short pipelines crossing road junctions, utility crossings and entrance

to carpark, in shallow depth. The completed works have demonstrated

its effectiveness due to fast mobilisation of plant, simple setup on site,

and flexibility in construction method to suit the space available. Due to

limited space, the tunnel excavation is generally carried out by hand tools.

There have been cases that unexpected full-face rock was encountered,

taking a long time for removal and affecting progress. Although problems

associated with safety, environment and ground stability could be aconcern, there is a growing demand in recent years that this method is

used to overcome site constraints, particularly those unexpected during

construction, thus minimising delay to the works.

All the above methods have merits and demerits. Their choice should be

based on technical compatibility with regard to ground and groundwater

conditions revealed by site investigation works, and other constraints

rather than only on cost. Detailed analysis of the risk, together with

the contingency plan, has to be given prior to finalising the decision.

Inspection and maintenance of tunnelling shields, TBMs and their backup

plant and equipment by competent personnel at regular intervals would

minimise the downtime and maximise the production. Since each project

is different in nature, it is advisable to consult with specialists in the field

and TBM manufacturers in the planning stage to ensure success.

Conclusion

The application of tunnelling and pipejacking techniques for drainage

pipeline construction in Hong Kong has proved to be promising, generally

with less construction time and disturbance to the public, when compared

with the conventional open-trench method. Some of the problems could

have been avoided or minimised had suitable technique been selected

based on detailed site investigation results and site constraints, and proper

planning provided in advance. It is essential to include comprehensive

rather than general requirements in the contract to fully cover each

activity of works, which should be practical and specific with regard

to the situation encountered, with the contractors responsibility and

actions being clearly defined, so that arguments between the clients

consulting engineer and the contractor on problems, when occurring,could be minimised. The experience, training and attitude of the working


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and supervising personnel also have a significant effect on the success

of works.

Through the rapid development of TBM technology, long, curved

pipelines have been carried out in irregular, alternating soil and rock

composition at different depths, in recent years. Tunnelling through the

already completed permanent shafts has also been carried out, with

proper control of alignment, at a number of locations, to suit the project

programme. This also gives flexibility in selecting shaft locations to get

rid of utility and traffic constraints, as well as the disturbance problems

to shops, in most cases.

By the installation of a sonic soft-ground probing system in the TBM for

detecting hard materials in front of excavation and an electronic tool

monitoring system for detecting the wear limit of disc cutters, which is

the recent technology advancement in TBM, the risk associated with

TBM stoppage, as a result of obstruction, which is a common problem

in pipejacking works, could be minimised.

Disc cutters have also been developed to have longer life and higher

capacity in dealing with the ground conditions likely to be encountered.

Artificial obstructions still have to be removed manually should there

be access in the front bulkhead of the TBM. Otherwise, the TBM would

stop in ground necessitating rescue operation. This can be carried out

by means of either a rescue shaft or a rescue tunnel, which is a time-

consuming and costly operation, affecting the progress of works and

disturbing the public. Therefore, site investigation should be carried outas much as possible at suitable locations before the tunnelling method

and TBM is finalised.

Tunnelling and pipejacking techniques will continue to become popular for

installation of drainage pipelines in the urban areas of Hong Kong as they

could eliminate most of the problems encountered by the conventional

open-trench method and hence enable the works to be completed with

least inconvenience to the public and minimum diversion of existing

utilities and services, and traffic. These techniques are continually being

refined and developed. Improvements cover both larger and smaller

diameters, longer drives, better control of alignment, faster and curved

driving, different ground conditions, and the ability to work deeper under

water. However, there are also certain constraints, such as no room for

construction of jacking and receiving shafts at suitable locations due

to congestion of existing utilities and hence the lack of space for theirdiversion or close proximity to shops, insufficient clearance between

overlying utilities and the jacked pipeline using TBM for advancement,

and unexpected underground artificial obstructions, which limit the

application of such techniques.

Acknowledgements

The authors wish to express their gratitude to the Drainage Services

Department of the Government of the HKSAR, for permission of extracting

the materials from the respective projects, to publish this paper. Special

acknowledgement is given to Herrenknecht AG, and CSM BESSAC, for

their permission of extracting the photographs from technical brochures

in making Figs 16, 17, 20 and 21, and Fig 19 respectively.

References

1. Thomson, J., Pipejacking and Microtunnelling. pp3-6. Black A&P. UK (1993).2. McFeat-Smith, I., Tunnelling in Hong Kong in the 1990s. Tunnelling in Hong

Kong Seminar. Hong Kong (1993).3. Research and Development Section. Trenchless Pipe Installation and Renovation

Techniques. Review of Pipe Jacking/Microtunnelling Techniques for Constructionof Drainage Pipelines. Research & Development Report No RD 1005/2. Drainage

Services Department, Government of the HKSAR. Hong Kong (2002).

4. Mok, W.W.S., Mak, M.K.W. & Poon, F.H.T., Sewer Installation by Pipejacking inthe Urban Areas of Hong Kong. Part I Planning, Design, Construction andChallenges. The HKIE Transactions. Volume 14, No 1, pp27-28. The Hong Kong

Institution of Engineers. Hong Kong (2007).5. Mok, W.W.S., Mak, M.K.W. & Poon, F.H.T., Sewer Installation by Pipejacking

in the Urban Areas of Hong Kong. Part II Performance of Works, LessonsLearned and Improvements Proposed. The HKIE Transactions. Volume 14, No1, pp34-35. The Hong Kong Institution of Engineers. Hong Kong (2007).

6. The British Tunnelling Society and The Institution of Civil Engineers.Specification for Tunnelling. pp36, 86-88 & 106. Thomas Telford. UK (2000).

7. Mok, W.W.S., Pipejacked Tunnels What to do If a Tunnel Boring Machine isStuck in Ground?. Trenchless Conference in Macau. Macau (2007).

Wilson W S MOK BASc BA CEng R.P.E. (Civil &Geotechnical) CSci MICE MIMMM MHKIE

Email: [email protected]

Ir Mok graduated from the University of Windsor

in Canada and has over 30 years practical workingexperience in a wide variety of geotechnical and civilengineering projects in both design office and site. Heis particularly experienced in dealing with design andconstruction associated with geotechnical investigations

and instrumentation, deep excavations, tunnels, groundimprovements, settlement analysis, reclamation, siteformation, slope preventive measures, foundations

and sewerage works. Ir Mok has been involved in the design, supervision andadministration of more than 16 km long trunk drainage pipeline construction inthe urban areas of Hong Kong, using different types of trenchless techniques from

relining, TBMs to hand-dug tunnelling, and has carried out extensive research onsuch. He is the author/co-author of several technical papers in this aspect, and hispaper titled Sewer Installation by Pipejacking in the Urban Areas of Hong Kong,in two parts, has been awarded the HKIE Transactions Prize 2007. He has beenSenior Resident Engineer on a DSD contract, which involved the construction of

4 km long trunk sewers, using pipejacking techniques.

About the Authors

K W MAK BSc Dip HE Delft PCLL MA Arb CEngMIEAust MICE MHKIE MIHT

Email: [email protected]

Ir Mak is currently Chief Engineer with DrainageServices Department. In the past few years, he hasparticipated in numerous large-scale and prestigiousdrainage and sewerage projects, including the Wan

Chai East and North Point sewerage project, the firsttertiary sewage treatment plant at Ngong Ping, thelargest ultra-violet disinfection facility installation atSin Ho Wan sewage treatment plant, as well as the5 km long rainwater-intercepting tunnel in Tsuen Wan.

Previously, he spent six years in the then Works Bureau dealing with slope andwater policies. During his earlier years with the Drainage Services Department, IrMak received post-graduate training in river engineering in the Netherlands, and

had then worked in the Shenzhen River Regulation Project. He obtained a Masterof Arts in the area of dispute resolution and arbitration. On top of his engineeringengagements, Ir Mak acquires legal qualification and is a non-practising Barrister-

at-law of the High Court of the H KSAR. Ir Mak is the co-author of the paper titledSewer Installation by Pipejacking in the Urban Areas of Hong Kong, which hasbeen awarded the HKIE Transactions Prize 2007.


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