Australasian Society for Trenchless Technologies - Guidelines for Hdd

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Australasian Society for Trenchless Technology

Guidelines for Horizontal Directional Drilling, Pipe Bursting, Microtunnelling and Pipe Jacking

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G:\01 Projects\ASTT\CPJP8029 - Development of Guidelines, Standards and Specifications\12 Native Documents\12.11Guidelines\CPJP8029-GUI-C-001 Rev 0 - Guidelines for Horizontal Directional Drilling Pipe Bursting Microtunnelling and PJ.doc

5.1 MT& PJ Process 13

5.2 MT& PJ Methods 16

5.2.1 Auger 16

5.2.2 Slurry 16

5.2.3 Vacuum Extraction 17

5.2.4 Pilot Tube 17

5.2.5 Open Hand Shield 19

5.2.6 Backacter and Cutter Boom Shield 19

5.2.7 Tunnel Boring Machine 19

5.2.8 Earth Pressure Balance 19

5.3 When to Apply MT & PJ 20

5.3.1 Capabilities 21

5.3.2 Limitation 21

PIPE BURSTING GUIDELINE 21

6.1 PB Process 22

6.2 PB Methods 23

CONTENTS

1.0 BACKGROUND 1

2.0 DEFINITIONS 13.0 INTRODUCTION 3

4.0 HORIZONTIAL DIRECTIONAL DRILLING GUIDELINE 6

4.1 HDD Process 7

4.2 HDD Methods 7

4.2.1 Pilot Bore 7

4.2.2 Reaming 8

4.2.3 Pullback 8

4.3 HDD Guidance Systems 94.3.1 Walkover 9

4.3.2 Hard Wire 10

4.4 When to Apply HDD 10


4.4.2 Limitations 11

5.0 MICROTUNNELLING AND PIPE JACKING GUIDELINE 12

6.0


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6.2.1 Pneumatic Bursting 23

6.2.2 Hydraulic Bursting 24

6.2.3 Static Bursting 25

6.2.4 Additional Pipe Bursting Methods 26

6.3 When to Apply Pipe Bursting 28


6.3.2 Limitation 30

6.3.3 Replacement Piping 31

7.0 FRONT END ENGINEERING 32

7.1 Technical Feasibility 32

7.2 Economic and Social Feasibility 33

7.3 Constructability 34

7.4 Geotechnical Investigation 35

7.5 Environmental Impact Assessment 36

7.6 Risk Management Assessment 37

8.0 REFERENCES 38


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1.0 BACKGROUND

This Guideline has been developed by the Australasian Society for TrenchlessTechnology for assisting users of Trenchless Technology in Australia and New Zealandin selecting and utilising the most suitable Trenchless Technology method available.

General information on current methods in Horizontal Directional Drilling, PipeBursting, and Microtunnelling and Pipe Jacking as a Trenchless Technologymethodology for installing pipe are provided, as well as means of determining whichTrenchless Technology methods is most appropriate.

This Guideline is intended as a guide to be used for information only and it does notreplace any existing manuals or standards. It is the user ’ s responsibility to ensure thatall relevant laws, standards and specifications are adhered to during the course of any

Works which use Trenchless Technology.

Additional information on each of the Trenchless Technology mentioned in thisGuideline can be obtained from the Australasian Society for Trenchless Technologywebsite:

• Standards for Horizontal Direction Drilling, Pipe Bursting, Microtunnelling & PipeJacking;

• Specifications for Horizontal Direction Drilling, Pipe Bursting, Microtunnelling &Pipe Jacking;

• National Utility Contractors Association Trenchless Assessment Guide, a web-based tool that can be used for identifying trenchless construction methodssuitable for a particular set of project attributes (i.e: diameter, length, depth,geological conditions and so on).

2.0 DEFINITIONS

A number of abbreviations and technical terms have been used in this guideline:

ASTT - Australasian Society for Trenchless Technology. (www.astt.com.au)

Auger - A method of moving material by use of rotating helical flighting, a screw

conveyor. The auger drill can also be used to excavate or drill through material.

CCTV - Closed Circuit Television - The use of video cameras to visually inspect theinstallation. Often used where manual entry is not feasible or possible.

CIPP - Cured-in-place pipe. The process involves the insertion of a resin-impregnatedfabric tube into an existing pipe by the use of water or air inversion.

Client - Person or company requiring the Works to be undertaken.

Contractor - Person, establishment, or company undertaking the Works required.

http://www.astt.com.au/http://www.astt.com.au/


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Cutter Head - The part of the MTBM that is responsible for excavation. Contains thecutter face, which is responsible for breaking, cutting and other wise removing earthfrom the desired bore path.

Entry Chamber- Also called insertion, thrust, drive or launching chamber or shaft.

EPBM - Earth Pressure Balance Machine. Mechanized excavating equipment similar tothe MTBM which uses excavated spoil to pressurise the machine and balance theforces experienced upon it during excavation.

Exit Chamber- Also called reception chamber or shaft.

Feasibility Study - Preliminary design and study to ascertain whether commencingthe works would prove logical.

Guideline - General information about an item, process, method, material, system orservice.

HDD - Horizontal Directional Drilling. A steerable trenchless method of installingunderground pipes, along a prescribed path by using a surface launched drilling rig.

HDPE - High Density Polyethylene. A strong, relatively opaque form of polyethylenethermoplastic made from petroleum. It has a dense structure with few side branchesoff the main carbon backbone.

IPBA - International Pipe Bursting Association.

ISTT - International Society for Trenchless Technology.

MTBM - Microtunnelling boring machine. Mechanized excavating equipment that isremotely operated, steerable, connected to and shoved forward by the jacked pipe ormechanical rods.

MT - Microtunnelling. Method for installing an underground service conduit to a highaccuracy using a microtunnelling machine. Generally guided by a laser and most often

used for the installation of gravity flow systems- ie sewer and stormwater or for otherservices where high accuracy is required.

NUCA TAG - National Utility Contractors Association Trenchless Assessment Guide.

Operator - Suitably trained or qualified person who operates machinery, aninstrument, or other equipment.

PB - Pipe Bursting. It is a In-Line pipe replacement technology that used to replaceutilities by a cone-shape tool inserted into the existing pipe and forced through andfracturing the pipe and pushing its fragments into the surrounding soil.

PE - Polyethylene Pipe. PE belong to a group of thermoplastics pipe commonly used in

gas and municipal applications.

PVC - Polyvinyl Chloride pipe. A PVC pipe is made from a plastic and vinylcombination material.

Pipe Jacking - Method for installing sewer pipe that serves as initial constructionlining and tunnel support, installed for stability and safety during construction, and assewer pipe. Pipe is shoved forward (or jacked) as the tunnel is advanced. The sewer orcarrier pipe is jacked forward as the tunnel is advanced.

PTMT - Pilot Tube Microtunneling. A MT method that involves drilling a pilot bore priorto tunnel excavation.


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Risk Management Assessment - The overall process of identifying all the risks toand from an activity and assessing the potential impact of each risk.

Shield - Often comprised of circular lining and the cutter head, protects the internalworkings of the MTBM from ground water, spoil and debris. Sometimes referred to as

part of the MTBM, the shield is pushed forward through the intended bore path by the jacked pipe.

Specification - A document that specifies, in a complete, precise, verifiable manner,the requirements, design, behaviour, or other characteristics of a system, component,

product, result, or service and, often, the procedures for determining whether theseprovisions have been satisfied.

Spoil - Material removed in the course of an excavation or drilling process.

Standard - A document that provides uniform technical criteria, methods andprocesses. Often establishes an engineering norm.

TBM - Tunnel Boring Machine. Mechanized excavating equipment that is steerable,guided and articulated, connected to and pushed by the jacked pipe.

TT - Trenchless Technology. Technology for installing pipelines or creating boreswithout the need of full surface excavation.

Vacuum Extraction - The use of high flow, high pressure air produced by a vacuumpower unit to transport cuttings from the excavation face to the ground surface.

VCP - Vitrified clay pipe. VCP is pipe made from clay that has been subjected tovitrification, a process which fuses the clay particles to a very hard, inert, glass-likestate.

Work - The project or task to be completed by the Contractor on behalf of the Client.

3.0 INTRODUCTION

This Guideline has integrated the necessary background information on three types ofTrenchless Technology methods to assist industry users to gain the knowledge in thefollowing fields:

• Horizontal Directional Drilling,

• Pipe Bursting,

• Microtunnelling and Pipe Jacking.

The objective of this Guideline is to assist Trenchless Technology users to comprehendthe possible benefits of select the applicable method for their project.

There are four sections in this Guideline. The first three sections providecomprehensive information outlining, the background of Trenchless Technology (HDD,

PB, MT&PJ), process, methods of available application, its capabilities and limitations.The last section outlines the importance of some front-end engineering considerationsencountered by users in the field of Trenchless Technology.


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A decision matrix is summarised in figure 3.1 to assist users through this Guideline.The decision matrix ensures a step by step process that assists the users on how theselected Trenchless Technology could benefit their project.

This decision matrix established the starting point for each selection process and

prompts the user to review the Standards and Specification applicable to the referralTrenchless Technology method selected. From this processes, the user will understandwhich method, or combination of Trenchless Technology methods that are suitable.


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FIGURE 3.1: TRENCHELSS TECHNOLOGY DECISION MATRIX


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4.0 HORIZONTIAL DIRECTIONAL DRILLING GUIDELINE

Horizontal Directional Drilling (HDD) is a trenchless excavation method originated inthe late 1960’ s by merging technologies prominent in the water wells and utilities

industry. HDD involves drilling along a desired pathway while simultaneously insertinga pipe into the new borehole. The HDD process is completed in three parts, the firstbeing the drilling of a pilot hole along the proposed centreline and the second beingthe enlarging of the hole with a reamer. The last step would be have the new pipe

installed behind the reamer during the last pass of the reaming process.. In any HDDworks, a major component of the drilling activities is the drilling fluid. In manyinstances and also in situations when the new pipe diameter is much larger than the

pilot hole, it is vitally important that the correct amount and mixtures of drilling fluid isresourced. The use of drilling fluid helps to prevent the potential collapse of the borepath, assists in the removal of cutting material produced by the drilling process, andreduces friction during the pullback of the new pipe process. Ensuring the correct borehole diameter may take more than one pass or reaming before the borehole is large

enough in diameter to install the proposed new pipe. The number of required reamingpasses may also be affected by geographical conditions. On the final pass with thereamer, the new pipe is attached to the reamer and pulled back through the boreholefrom the exit point to the drill rig.

HDD operations are performed using a drill rig situated on the surface (Figure 4.1) andas such do not need a huge entry chamber excavated, but generally only require asmall slurry containment chamber in order to commence the process. The self-contained rig usually consists of a powered rack which pushes the drill into the ground,and a motor and drive system to rotate the drill string. The rig is securely fastened tothe ground before the operator proceeds to drill and steer the drill head and rods alongthe desired directional path. The desired directional path is followed and tracked using

a guiding or tracking system. The most common guiding and tracking systems are the

walkover, and the hard wire steering system. Both systems are discussed in Section4.3.

FIGURE 4.1: DRILL RIG (Picture Courtesy of UAE)


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HDD is an attractive option for installing pipelines under bodies of water, accessrestricted, protected areas, or urban spaces where the social and environmental costsof construction (and destruction) of surface are too high. High initial HDD capital costs

may be offset by lower labour costs and faster completion of works when compared to

conventional open trenching methods.

4.1 HDD Process

The HDD process requires the use of a drill rig, drilling head, drilling fluid, a reamer,drill rods and a range of ancillary equipment, including pulling heads, swivelconnectors, and a pipe roller. Although implementation of HDD does not require an

entry chamber, an exit chamber is often excavated to contain drill slurry for collectionprior to recycling or removal. From the drill rig, the drilling head navigates through theground along the desired bore path and past any obstructions. The resultant spoil isremoved during the drilling process with a slurry (or drilling fluid) comprised of

Bentonite and sometimes a composition of water and polymer. This slurry is also usedin the drilling process to stabilise and lubricate the borehole as well as acting as acooling agent for the drill head and embedded location transmitter.

Although the slurry is the method in the HDD process that help keeps the boreholeopen in the drilling process it will harden or cure like grout or cement and equalise withthe natural ground conditions to seal the borehole.

A commonly used HDD electronic beacon (walk-over) guidance system utilises a

transmitter, located in the drill head, receiver, and remote monitor to transmit andreceive signals along the designated drill path, from the surface entry point to the finalexit point. This monitoring process allows the drill head’ s position, depth andorientation to be determined at all times, to avoid any existing utilities while drillingand entering unfavourable ground formations.

Where there is a risk of damage to existing utilities from ground heave, small potholesmay be required to be excavated in the vicinity of where HDD bore path and theexisting utilities crosses. This effectively relieves the pressure forces on the utilitiescaused by any ground movement.

A containment chamber is normally dug next to or at the exit chamber where the HDD

machine is located. This is for processing the slurry used during the HDD work. Aseparate mud recycling system may also be situated in this containment chamber,dependant on the size of the works.

4.2 HDD Methods

4.2.1 Pilot Bore

The HDD process involves the use of a drill rig to drill the pilot borehole from thesurface through to an exit chamber, using a drill head situated at the end of a string ofdrill pipes. The position of the drill head is monitored by a guidance system, via atransmitter fitted in the drill head. The pilot bore usually ranges from 75mm to 150mm in diameter. Figure 4.2 below is an illustrated example of a typical pilot bore.


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FIGURE 4.2: GENERAL EXAMPLE OF A PILOT BORE (Graphic Courtesy of TT)

4.2.2 Reaming

After the completion of the pilot borehole, a reaming bit is attached to the drill pipe atthe exit pit. The is reamer pulled back through the pilot bore to enlarge the borehole.It may take many passes of the reamer before the borehole is sufficiently wide enoughto accommodate the new pipe. Generally, a final reamed borehole of 1.5 time biggerthan that of the new pipe outer diameter is required. This allows for the “return” of thedrilling fluids, spoils from the new pipe surrounding, and provides room to achieve asafe bending radius of the pipeline. Maintaining the borehole and flushing out theexcess spoils and reducing of drilling friction is done by injecting slurry into the

borehole.

4.2.3 Pullback

The pullback process is carried out once the reaming process has been completed. Thenew pipe is attached to the drill pipe using a pull head and a swivel (to preventrotation of the pipeline during the pullback process), together with the reamer which islocated between the drill string and the pull head. The reamer ensures the boreholeremains open during pullback and removes any additional loose debris within theborehole. This also allows lubricating fluid to be pumped through the bore. Thepullback process is completed when the new pipe reaches the drill rig, at which timethe pull head is disconnected and the tie-ins are started. Figure 4.3 illustrated exampleof a typical reaming and pull-back process.


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FIGURE 4.3: GENERAL EXAMPLE OF A REAMING AND PULLBACK SYSTEM(Graphic Courtesy of TT)

4.3 HDD Guidance Systems

Most HDD systems - especially long distance surface launched operations - require anaccurate guidance system. The most common guidance systems are known as ‘walkover’ or ‘hardwire’ systems. Figure 4.4 below is an il lustrated example of a typical ‘walkover’ guidance system.

FIGURE 4.4: GENERAL EXAMPLE OF A WALKOVER GUIDANCE SYSTEM(Graphic Courtesy of Digital Control Incorporated)

4.3.1 Walkover

A Walkover systems operates with the use of a radio signal with a transmitter placedwithin the drill-pipe (Figure 4.5). The surface walkover receiver picks up a signaltransmitted from the drill head in the borehole. Transmitted information, including drillhead location and orientation, beacon battery status and beacon temperature, can bereceived and interpreted by the operator. The receiver can pick up the transmittedsignal at distances of up to 40m away from the drill head. The main limitations of


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walkover systems is the requirement for the receiver operator to walk directly abovethe of the bore which cannot always be achieved e.g. drilling under a body of water.The ability of the receiver to receive signals also decrease with depth. In these

circumstances, the hardwire guidance system option should be considered.

FIGURE 4.5: GENERAL EXAMPLE OF A TRANSMITTER PLACED IN DRILLING PIPE(Picture Courtesy Of Digital Control Incorporated)

4.3.2 Hard Wire

Hardwire (or wire line systems) utilises a cable running through each drill string to

transmit data from the drill or bore head beacon to the control console. Thisovercomes the depth limitation of the walkover system, and has a higher degree of

accuracy. This system can be used in any environment, providing the beacon isdurable and shock and vibration resistant. The disadvantages of the hardwire system(apart from initial capital cost) is that it is time consuming and therefore reducesproductivity, because the wire often interferes with threading of additional rods to the

drill string.

4.4 When to Apply HDD

HDD is most suitable for the installation of pressure lines and protection pipes indiameters of up to 1.2m. The HDD drilling process performs well in a range of groundconditions including silt, sand, clay and many solid rock formations.

Calculation of the correct pressure and amount of slurry to utilise is another majorconsideration for HDD projects. There are a number of potential risks involved,

including collapse of the bore hole – caused by loss of slurry, improper slurry, wateringress, and surface heaving (caused by excessive slurry pumping), incorrect surfacedepth (too shallow), or pulling the reamer through too quickly, which can be

minimised with an effective drilling and drilling fluids plan.


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4.4.1 Capabilities

HDD works best when installing pipes with diameters up to a maximum of 1.2 meters. Alternative TT methods have been developed that normally provide a better success

rate in installing larger pipe diameters, in differing and deeper ground conditions, e.g.MT & PJ.

The capability of HDD, as with other trenchless technology methods, to lay conduitsand pipes in the ground without the need for intrusive open trenching ensuresminimum disruption to the environment and surrounding surface, and normally allowsthe installation of these conduits or pipes within a shorter time frame.

Excellent steering capabilities give HDD a major advantage over other TT methods.When obstacles are encountered in the drilling process, the drill head can be retractedand re-routed around the obstacle.

Since a HDD process can be launched from the ground surface and requires arelatively shallow containment chamber, the set up time and project costs can be

considerably reduced. Additionally, unlike other TT processes, HDD is a continuous drillmethod, which facilitates further reductions of time and costs. The drive length thatHDD can achieve is also the longest of any unmanned trenchless method. Figure 4.6illustrate a 477m bore distance under a harbour canal in Germany.

FIGURE 4.6: HDD UNDER CANAL

4.4.2 Limitations

HDD does not perform as well in locations with gravel soils, boulders, and compactstone layers. The changing ground formations and mixed soils create difficulty in

controlling the drill direction (e.g. Sandy soil or limestone layers). A chance ofexperiencing drilling fluid loss, due to voids within the change of soil mixture, is alsovery high.


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Coarse-grained soils, or soils that contain boulders or cobbles, encountered during theHDD process, can result in an increase in the overall project duration and cost.Thorough site investigation of the proposed drill path has proved to be a major reason

for, and key to, successful HDD projects.

5.0 MICROTUNNELLING AND PIPE JACKING GUIDELINE

Microtunnelling (MT) and Pipe Jacking (PJ) are Trenchless Technologies often utilisedto install pipes under protected sites and busy urban areas. MT and PJ is a means ofinstalling pipes, ducts, and culverts below ground in a wide range of soil conditions. Itis a very popular option for installing brittle pipelines such as concrete and installed inareas where open excavation would prove too costly, socially unacceptable (trafficdiversions and route blockages), economically damaging to local business, and or

environmentally unacceptable (surface damage causing distress to flora and fauna).

MT and PJ also require less labour than conventional open trenching methods andtherefore can be a very cost effective solution. It achieves tolerances of +/- 25mm in

line and grade.

Microtunnelling

MT is defined as a remotely controlled technique that provides continuous support tothe excavation face that does not require personnel entry into the tunnel1 . The tunnelboring machine, if required e.g. for changing cutters, can be accessed from a accessshaft.

Entry pipes are jacked to an exit shaft by means of a jacking frame. At the same time,

ground displacement or full-face excavation of the tunnel face is carried out. Theminimum depth of cover to the pipe being installed using the MT process is normally2m or 1.5 times the outer diameter of the pipe being installed, whichever is greater.Figure 5.1 show an example of an MTBM.

FIGURE 5.1: MICROTUNNEL BORING MACHINE (Courtesy of Akkerman)


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Five independent systems are incorporated into a Microtunnelling system. They are asfollows:

(1) Microtunnelling Boring Machine (MTBM)

(2) Jacking and propulsion system

(3) Spoil removing system

(4) Laser guidance and remote control system

(5) Pipe lubrication system

Three types of MTBM will be discussed in this Guideline, they are the Auger system,Slurry system with Vacuum extraction, and Pilot Tube MT system (PTMT).

Pipe Jacking Pipe Jacking is a reference to using powerful hydraulic jacks to push specificallydesigner pipes through the ground behind a shield at the same time as excavation istaking place within the shield. These methods provide a flexible, structural, watertight,finished pipeline as the tunnel is excavated.

Shields are open to the face where manual or mechanical excavation is affected.Manual excavation is done in an open hand shield, whilst mechanical excavation isdone using either a cutter boom shield (cutter installed in an open face shield) or abackacter shield (backacter installed in an open face shield).

Open hand shields are restricted to a minimum of 1200mm internal diameter, and areonly suitable for short drive lengths, due to occupation health and safety reasons.

Manual excavation should only be considered if other mechanised methods areunsuitable. Suitable equipment, work methods and practices must be instigated to limitexposure of workers to noise and vibration, and other hazards. These must beidentified in a Risk Assessment, and mitigated prior to commencement of any Works.

The fundamental difference between MT and PJ is that workers are required to operateinside the installed pipe during the manual PJ process, whilst MT is achieved with theuse of a remotely controlled MTBM. A number of excavation systems are available forPJ which includes manual, mechanical and remote control. This means that PJ methodare used to install pipes in the range of 150mm to 3000mm. Excavation at the face canbe either manual or mechanical, and is carried out inside a shield (open face) or by aTBM (closed face).

5.1 MT& PJ Process

5.1.1 Microtunnelling Process

All MT processes encompass a Microtunnelling Boring Machine (MTBM), which isessentially a combination of, a rotating cutting head and shield. It also includes a jacking system, automated spoil transportation system, guidance and direction controlsystems and pipes to be jacked into position (jacking pipes). Microtunnelling is also


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considered as a cyclic jacking process, which is an unmanned method of tunnelling. MTapplications range in diameter from 25mm to 3500mm, with the most commonapplications being in the range of 600mm to 1200mm.

The Microtunnelling process and spoil removing system are discuss as follow.

• Auger system: an auger chain installed within the jacked pipe transports thespoils to a muck skip under the jacking frame. When this is full, the operation ispaused to allow for the mud skip to be hoisted to the surface and emptiedbetween pipe changes.

• Slurry System: In situations where difficult ground conditions are encountered, or

when there are high groundwater heads (> 4m), recirculating slurry systems maybe utilised to remove the spoil. The slurry is a mix of Bentonite and watersometimes including for a polymer, in which the excavated spoil is suspended. Itis then pumped out via a system of pipes established in the jacked pipe to asolids separation system, at which point the spoil is filtered and separated from

the slurry. The filtered slurry is subsequently recirculated and reused within theslurry system.2

• Vacuum: Vacuum extraction can be used in ground conditions ranging from

clayey sands to rock. It cannot be used in soft soils such as non-cohesive siltsand sands below the water table. This method of spoil removal method iscommonly applied with the slurry system.

• Pilot tube microtunnelling (PTMT) utilises the same steering head used for

Horizontal Directional Drilling (HDD). Using a 360° rotatable shoe shaped drillhead to provide the resultant force from the soil makes the pipe string highlysteerable and accurate. The drill pipe is used as an alignment guide for theproduct pipe after the drilling of the pilot tube has been completed. The

displaced soil is excavated through the product pipe using simple auger systems.PTMT uses relatively low level technology and therefore has lower capital coststhan other MT methods. This method can work from very small access shafts,e.g. the existing access chambers as the entry and exit chambers. Accuratealignments of +/- 25 mm are a achievable by the drill pipe PTMT systems can beused for installing pipe lengths of up to 150m in length, which pipe diameters

ranging from 150mm to 600 mm.3

Pipelines installed using MT provides a high degree of accuracy via the utilisation oflaser and CCTV guidance systems. Steering is achieved with the use of steering rams inan articulated joint, normally at the mid point of the MTBM. Most guidance systems

work so that at any time the exact position of the TBM and the deviations from thedesigned tunnel axis, as well as the predicted movement tendency of the TBM areavailable to the machine operator. A typical MT guidance system is shown in Figure5.2.

A lubrication system reduces the risk of pipe damage on most microtunnelling works,and is particularly useful for longer pipe drives. The lubricant is applied to the exteriorof the pipeline during installation to minimize pipe friction and to ensure that the pipecan be installed from the drive shaft to the exit shaft within the safe working loadrating of the pipe.


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5.1.2 Pipe Jacking Process

Pipe Jacking processes usually require the construction of an entry and exit shafts. Thesizes of both shafts will vary according to the excavation methods employed for each

project.

Different types of PJ methods are discussed further, in next section of this guideline.The mechanical excavation methods employed are similar to those used in other formsof tunnelling.

A thrust wall is constructed to provide a reaction against the jacking force. Manydifferent types of thrust wall design should be consider when vary ground conditions

are encountered, to provide sufficient reactions against the jacking force. A thrust ringis used to transfer the jacking forces around the circumference of the pipe during the jacking process to prevent damage to the pipe.

FIGURE 5.2: TYPICAL MT GUIDANCE SYSTEM (Graphic Courtesy of Herrenknecht)

FIGURE 5.3: AN EXAMPLE OF JACKING FRAME (Courtesy of Bradshaw Corp)


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The jacking system, comprises of jacks, a jacking frame and a bench (as seen in figure5.3), can have a jacking capacity of 1000 tons. 2 The frame is designed to provide thelevel of pressure required by the MT shield. The required jacking force (JF) can beestimated by:

JF = π × OD× L× F , where4

OD = Pipe Outer Diameter (m)

L = Drive Length (m)

F = Friction Factor (tons/m2)

5.2 MT& PJ Methods

5.2.1 Microtunnelling Method

The three types of MT methods outlined below are the auger, slurry (with vacuumextraction) and PTMT systems.

Auger

The auger method makes use of a unidirectional large diameter auger for excavation.3 This method also uses helical auger flights rotating in a steel casing to remove spoil

back to the drive chamber.1 The spoil is transferred to a mud skip, usually locatedunder the jacking frame and is emptied at each pipe change. Auger boring cannotcontrol the pressure at the MT head, nor can it deal with harder, granular soils andhigh water tables. Auger boring is typically used to install pipelines of up to 150m in

length, ranging from 250mm to 1000 mm in diameter.3 Generally, auger type MT is

limited to less than 3m below groundwater level.4 This is to ensure the operation is notaffected by the hydrostatic pressure generated by the groundwater.

Slurry

The slurry method of soil excavation utilises a watertight head at the front of theMTBM to prevent the ingress of soils and liquids. The movement of the slurry iscontrolled by variable speed pumps and monitored by pressure sensors in the MTBM.The excavated spoil is extruded through the boring face into a mixing chamber whereit is combined with, and suspended in, a slurry. The slurry (and suspended excavated

material) is then transported to a solids separation system.2 This system allows theslurry to be recycled and reused in the process.

The slurry Microtunnelling excavation process can work in high water table conditionsand in soft soils (without dewatering or ground treatment being required), since thepressure of the slurry is used to balance the groundwater and face pressure. Slurry MTsystems can operate for pipelines ranging in diameter from 250mm to 3000 mm and

can be installed to distances of over 2500 m.3


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Vacuum Extraction

The use of vacuum extraction for the removal of spoil from the cutting head is used infirm soil ground -clayey sands, clays- to rock. It is not suitable for soft soil below thewater table. All ground water created by the microtunnelling process and in the shaft

needs to be managed by recycling, treatment, then on-site disposal or off-site disposal.Drilling in a downhill direction causes the ground water to flow to the face which willneed to be managed.

Pilot Tube

Some specialised systems exist in which the cutter head can be collapsed inward and

be withdrawn back through the jacking pipes. In other systems which use mechanicaldrive rods rather than the jacking pipes to impart the thrust to the MTBM, free-boringis possible in self-supporting ground. Free-boring allows a microtunnel to be bored to a

dead-end and the head withdrawn back through the microtunnel thus eliminating theneed for an exit shaft.

Shafts often need to be specifically designed and built, based on the selected MTBMselected. Different methods of constructing the shafts exist, including sheets andshoring, trench boxes, driven sheet piles, and linear plates. If, for geotechnical oreconomic reasons, dewatering or grouting is not feasible, then concrete caissons maybe used to construct the shaft. Interlocking sheet piles may be used if a deep shaft isrequired in a high water table environment. Cantilevered bracing is preferred forshallow shafts. However, for excavation depths of greater than 3m, lateral bracing may

be required.1 The ground condition of the entry shaft should also be taken intoconsideration to prevent in flow and MTBM instability. Figure 5.4 shows a typical MTsystem.

FIGURE 5.4: TYPICAL ARRANGMENT OF MICROTUNNELLING METHOD(Graphic Courtesy of ISTT)

5.2.2 Pipe Jacking Method

PJ is a cyclic procedure that uses the thrust power of the hydraulic jacks to force thepipe forward through the ground as the pipe jacking face is excavated. The spoil istransported through the inside of each pipe to the drive shaft, where it is removed anddisposed off. After each pipe segment has been installed, the rams of the jacks are


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retracted so that another pipe segment can be placed in position for the jacking cycleto begin again.

There are five types of PJ excavation methods, Open Hand Shield, Cutter Boom Shield,Earth Pressure Balance (EPB), Backacter Shield, and Tunnel Boring Machine (TBM), as

indicated in Figure 5.5. The choice of excavation method selection will also depend onthe appropriate ground support technique.

OPEN FACE CUTTER BOOM EARTH PRESSURE BALANCE MACHINE

BACKACTERS TUNNEL BORING MACHINE

FIGURE 5.5: PIPE JACKING EXCAVATION METHODS

SOIL EXCAVATION METHODS METHODS OF SPOIL REMOVAL

Open Hand Shield Aguer system

Backacter Shield Slurry and pressure

Cutter Boom Shield Vacuum Extraction

Tunnel Boring Machine Wheeled carts or skips

Earth Pressure Balance Machine Auger system or Belt and Chain conveyors

TABLE 5.1: PIPE JACKING EXCAVATION METHOD

The spoil removal systems listed in table 5.1 function for both MT and PJ systems. Thespoil is removed from the back of the cutting head and transported to the entry shaftusing one of the methods listed. The spoil is then removed to the surface from theshaft.


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The appropriate spoil removal system will be dependent on the available space insidethe shaft and tunnel, the method of soil excavation, and the mechanism of the facepressure balance and the total tunnel length.

Open Hand Shield

Open Hand Shield must be equipped with at least four steeling jacks spaced aroundthe lead pipe. The shield should be of a diameter slightly greater than the outside pipediameter to allow it to be steered and provide an annulus for lubrication. The aspectratio of diameter to length of a shield can be critical to its steering ability.

Backacter and Cutter Boom Shield

Backacter and cutter boom are essentially open face shields with mechanical means ofexcavation. The backacter type is suitable in semi-stable to stable soil up to strongcohesion values. The shield cutter is more suitable in higher strength soils, marls and

some rock types. The excavation may proceed with a slight overcut to the shieldcircumference in firm ground. Alternatively the shield can be used to trim the underexcavated face. In lose ground conditions, consideration should be given to theprotective hood and ground breasting boards or sand tables.

Tunnel Boring Machine

A Tunnel Boring Machine (TBM) is essentially a shield with a rotating cutting head.

They can vary in size from 1m to over 15m in diameter. However, the installationmethod changes from pipe jacking to segmented inserts for diameters greater thanabout 3600mm. Since ground conditions can vary significantly, a wide range of cutting

heads are available to suit. The choice of which type of TBM is preferential depends

largely on the type of geology that will be encountered and the speed of excavationthat is required.

The process involves using hydraulic jacks to push specially designed pipes and ormechanical rods through the ground behind a shield, while at the same timeexcavation of the spoil is carried out within the shield. This jacked pipe and ormechanical rods in turn provides forward thrust to a MTBM situated at the head of theshield. The MTBM is remotely operated, steered, and guided by an operator located ina control room. Spoil removal is done by a variety of methods including slurry,conveying and solid pumping.

Earth Pressure Balance

Earth Pressure Balance (EPB), another excavation method used in PJ, excavates byutilising an EPBM. The cutter head is much like the cutter head in the slurry method.However, in this process, the chamber in the cutting head is kept full of excavatedmaterial under pressure to counter balance the geological pressures encountered atthe front of the MTBM. The spoil is transported via a screw auger and then removedeither by a conveyor system, which transports the spoil from the head to the muck

skip, or by a pumping system.3 Coarse granular soils may present problems in

maintaining a seal in the rising auger flights which in turn may throw off pressure andgroundwater control. For this reason, the EPB system is best suited for fine cohesive


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soils and relatively low groundwater heads.3 EPB MT pipelines can range in diameterfrom 250mm to 3000 mm and can be installed to distances of over 2500 m.

5.3 When to Apply MT & PJ

Due to the use of guidance and control systems (fitted in the shield), Microtunnellingand Pipe Jacking is suitable for installations where high accuracy is required in the lineand level of the pipeline. Typical fields of application include sewage and drainagelines, gas and water mains, oil pipelines, electricity and telecommunications cableinstallation, and culverts. The technique is capable of negotiating obstacles such asroads, railways, rivers and buildings, which minimises the surface disruption associatedwith regular open cut pipe laying methods. Table 5.2 shows the general assessment oftrenchless methods against different soil types.

For any MT and PJ process, the correct pipe selection is critical. The ultimate successand quality of the work is largely affected by the choice of pipe. The jacked pipes

require high strength and stiffness to be able to withstand the drive forcesencountered. The pipes form a continuous string in the ground, which forms the final

pipeline. 5

There are very limited repair options for non-man entry pipes, if the pipe cracks or failsduring the installation process. In the case of a pipe failure near the beginning of thepipe string, additional sections may be able to be added and jacked until the failed pipecan be removed from the exit shaft. The pipe selected must be able to withstand thethrust force of the jacking unit.

PARAMETER PIPE

JACKING

MT

AUGER MT SLURRY

MT VACUUM

EXTRACTION PILOT TUBE

Hard rock Possible No Possible Yes No

Soft rock Possible No Yes Yes No

Hard Clay Yes Yes Yes Yes No

Soft Soils Possible Possible Yes Possible Yes

Sand & Gravel Possible No Yes Possible No

Sand Possible Yes Yes Possible Yes

Cobbles/boulders

Possible No Possible No No

Obstruction Possible No Possible Possible No

Below water

table Possible No Yes No Possible

TABLE 5.2: GENERAL ASSESSMENT OF TRENCHLESS METHODS

AGAINST TYPICAL SOIL AND ROCK TYPES3

Note: Possible - Indicates that the method may be suitable in specific circumstancesbut requires further investigation.


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5.3.1 Capabilities

Microtunnelling and pipe jacking is a versatile technique that can achieve a very high

degree of accuracy (usually with a deviation of less than 2cm over 100m) 4 and grade.

Many MT methods have been designed that are able to deal with a variety of groundconditions. The boring heads can be designed to crush boulders with a diameter of lessthan 20% of the machines diameter and for tunnelling through hard rock (usually with

the addition of drag bits, button cutters or disc cutters).4

Microtunnelling and pipe jacking is usually a relatively quick process, thereby reducingassociated labour costs and personnel risks. Unlike standard trenching methods, alarge increase in depth typically only results in small increases in relative cost.

Furthermore, the length of drive can be virtually unlimited.6 The product pipe can be

jacked directly without the need for a separate casing pipe,2 further reducingequipment and installation costs. MT is economically feasible if the average depth ofthe pipe exceeds 6m, or if the depth of cover is greater than 1.5 m and the depth of

cover to pipe diameter ratio is 3:1 or greater.4

5.3.2 Limitation

MT & PJ methods often have the following limitations:

• High initial capital cost.

• Can have difficulties in soils containing boulders with sizes greater than 20% ofmachines diameter.

• MT is unable to make rapid changes in alignment or level.6

• Auger type MT machines are usually limited to tunnelling less than 3m belowground water levels4.

6.0 PIPE BURSTING GUIDELINE

Pipe bursting (PB) is a trenchless method/process which is used to replace defective orunder capacity pipelines by utilising the original pipe alignment. The process uses a

bursting head to crack the defective installed pipe and displace the cracked pipeoutwards into the surrounding soil. A new replacement pipe of the same or larger

diameter is simultaneously pulled in behind the bursting head.Pipe bursting, being a trenchless tunnelling method, is an ideal solution for situations

where open cut methods are difficult to implement, or where the associated costsconstruction, economic, social, and environmental may prove prohibitive. The use ofPB avoids many obstacles and costs associated with conventional open trench pipe

replacement methods, such as road closures, traffic congestion and diversion, loss ofbusiness due to construction and disruption of natural and urban habitats. PB projectsalso significantly reduce rehabilitation costs for restoring the affected landscape to its

initial condition due to less open excavation, and can be completed in shortertimeframes. A typical example of a PB process is shown graphically in Figure 6.1.


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FIGURE 6.1: TYPICAL EXAMPLE OF PIPE BURSTING PROCESS (Courtesy of ISTT)

6.1 PB Process

The main components involved in a pipe bursting operation are:

• Winch,

• Hydraulic jacking unit (not always required),

• Guide (cable, rod, chain) in held in tension,

• Bursting head and,

• Replacement pipes.

The general process for pipe bursting requires the inserting of a guide cable, rod orchain from an excavated exit chamber, through the installed defective pipe, to anexcavated entry chamber, see (Figure 6.2). In addition to the entry and exit chambers,access chambers are also excavated at locations and crossing points. These are usedto enhance the monitoring of the pipe bursting process.

A winch is installed at the exit chamber that is used to pull in the guide cable from theentry chamber (for this guideline the cable process is discussed, the specific road,chain or cable would be determined for each PB process, however the general processis similar for all processes). The guide cable is attached to both the winch and thebursting head in the entry chamber, and is pulled back to the exit chamber, draggingthe replacement pipe into position. In the process of being pulled back, the originalpipe is burst and the pipe fragments are forced outward into the surrounding soil bythe bursting head.

The bursting head, which is bigger in diameter than the existing pipe effectivelycreates a new bore from within the ‘host’ old pipe, pulls and simultaneously installs anew pipe during the PB process.


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The most commonly utilised PB methods fall into the following categories:

(a) Pneumatic bursting.

(b) Hydraulic bursting.(c) Static bursting.

Additional Pipe Bursting methods, including Pipe Splitting, Pipe Implosion, Pipe Eating,Pipe Ejection and Extraction, and Pipe Reaming, are also used in the industry, althoughfar less frequently.

The decision on which method to use is dependant on the type of installed pipeneeding replacement, the actual replacement pipe, and the conditions likely to beencountered in the process.

FIGURE 6.2: EXAMPLE OF EXCAVATED CHAMBER (Picture Courtesy of TT.)

6.2 PB Methods

6.2.1 Pneumatic Bursting

The pneumatic pipe bursting method utilises a bursting head that bursts the defectivepipe with a horizontal hammering force (Figure 6.3). The bursting head delivers animpact load thereby applying a hoop stress into the pipe, causing it to burst under theapplied tension, and induces a force in the longitudinal direction causing shear failure.


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The bursting head is guided through the pipe with a tensional cable inserted thoughthe pipe prior to bursting. The tensioned cable ensures that a continuous constantcontact between the bursting head and the defective pipe is maintained and assists in

keeping the new pipe within the alignment of the host pipe during the jacking process.

With PB, it is the hammering force rather than the constant pulling tension of the cablethat causes the host pipe to crack. The bursting occurs using powered hammer strikes,which provides the breaking force and allows for the progression of the head through

the host pipe.

The bursting head is powered by compressed air connected to the back end of thebursting head which runs through the inside of the new pipe string to a compressor

located on the surface. Operator intervention is minimal in the bursting process, as thecompressor and winch are set at constant pressure and tension, until the pipe sectionbursts through into the exit chamber and the installation of the new pipe is completed.

FIGURE 6.3: AN EXAMPLE PNEUMATIC BURSTING HEAD

(Graphic Courtesy of Miller Pipelines)

6.2.2 Hydraulic Bursting

Hydraulic pipe bursting utilises a bursting head that expands radially under hydraulicpressure to burst the defective installed pipe from the inside (Figure 6.4). Using axiallymounted hydraulic piston in the hydraulic bursting head, the bursting head expands,

causing the pipe to burst and contracts allowing the bursting head to be advancedincrementally, by a tensional cable that guides the bursting head and the newreplacement pipe forward into the space created. This process is repeated until thehost pipe is eventually replaced with a new pipe.

Hydraulic pipe bursting is powered by portable power unit installed on the surface

similar to the Pneumatic PB method. The hose is connected to the bursting head byinsertion through the new pipe from the power unit to the bursting head.


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FIGURE 6.4: EXAMPLE OF AN HYDRAULIC BURSTING HEAD

(Graphic Courtesy of Miller Pipelines)

6.2.3 Static Bursting

Static pipe bursting methods burst the defective pipe by pulling the bursting head from

the exit chamber with a cable or rod attached to the bursting head (Figure 6.6). Thestresses created by the radial force applied to the pipe wall by a cone shaped burstinghead pulled into the pipe cause the host pipe to rupture.

A winch or hydraulic system is used on the surface by the entry chamber to connect tothe cable or rod which are used to apply a pulling force to the cone shaped burstinghead.

When utilising a rod assembly, bursting rig, the rods are initially inserted into the

defective host pipe one at a time, starting from the exit chamber, with subsequent

rods attached after each push until the entry chamber is reached. The new pipe isattached to the bursting head in the entry chamber, and pullback is commenced from

the pulling system at the exit chamber, while a pushing system inside the entrychamber assist with bursting the host pipe and pushing in the new pipe. The rods areremoved one at a time after each bursting pull until the new pipe reaches the exitchamber. The rods used in bursting rigs can be either ladder rods or threaded rods,although industry experience indicates that that ladder rods have more advantages.Ladder rods are connected via quick couplings and this ensures a traction and thrustresistant joint. Additionally, greasing is not required on ladder rods because they haveno threads. Figure 6.5 show a example of rods bursting system.


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FIGURE 6.5: STATIC ROD BURSTING SYSTEM (Graphic Courtesy of TT)

If a cable and winch system is used, the pulling process is able to continue withminimal interruption once the pipe bursting operation has commenced. However, this

system cannot generate the same pulling forces as rod systems7 as the rod system issetup with anchors at both the entry and exit chambers. Unlike the cable systemwhere the hydraulic unit is stationed on the surface of the entry chamber withoutanchoring onto any support.

FIGURE 6.6: STATIC BURSTING HEAD (Graphic Courtesy of Miller Pipelines)

6.2.4 Additional Pipe Bursting Methods

Pipe Splitting, Pipe Implosion, Pipe Eating, Pipe Ejection and Extraction, and PipeReaming are not commonly used in pipe bursting systems, and are normally onlyutilised for specific applications or situations. However, many of these methods havebeen refined and/or combined with common pipe bursting systems (Static andPneumatic) mentioned in earlier sections.


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Some industry pipe bursting methods effectively combine static pipe bursting with pipesplitting; or combine pipe reaming with pipe splitting; or also combine pipe splittingwith any one or two other combinations mentioned above.

In many pipe bursting operations the use of pipe splitting combined with other pipe

bursting methods has been gaining popularity due to increases in burstingproductivities.

Pipe Splitting

Pipe splitting is similar to the static method but utilises a bladed head to cut throughthe wall of the defective pipe rather than burst it (Figure 6.6). This method is usedprimarily for splitting ductile pipe such as steel or iron, but is also applicable for plasticpipes.

FIGURE 6.6: PIPE SPLITTING (Picture Courtesy of AUI INC)

Pipe Implosion

Pipe implosion is also similar to the static PB method. The defective pipe is first brokeninwards by using a cylinder shaped crushing head, which is slightly larger than the

existing pipe and contains steel blades radially extended from its centre and then thepipe fragments are displaced outwards with a following steel cone bursting tool. Pullingin of the new pipe is achieved using a rod assembly.

Pipe Eating

Pipe eating is a modified microtunneling method developed for replacing predominantly

concrete sewer pipe. A microtunneling boring machine (MTBM) crushes the defectivepipe which is then removed by a circulating slurry system. The new pipe issimultaneously jacked in behind the MTBM. The replacement pipe path is not limited

to following the alignment of the existing pipe path, which may not be ideal in line andlevel, as the machine is capable of “eating” not only the old pipe, but the ground aswell. This method however requires a jacking frame to be inserted in the chamber to jack the MTBM and replacement pipeline forward.

The advantages of using this system remain the fact that the whole of the old pipematerial is removed in the process, and having the ability to accurately control the lineand level of the new replacement pipe.


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Pipe Ejection and Extraction

Pipe ejection is a modified pipe jacking method. The replacement pipe is used to pushthe old pipe out. The new pipe is jacked forward in segments pushing against the oldpipe, which results in the old pipe being ejected at the exit chamber, where it is broken

up removed.

Conversely, pipe extraction is a modified static PB method. In this case, the

replacement pipe is used to pull the old pipe out. This requires the use of a pullingdevice (rod assembly) situated in the exit chamber, and a rod string fed back to theentry chamber. The pulling device pulls in new replacement segments, which in turn

pulls the old pipe back to the exit chamber. Once the old pipe is pulled back into theexit chamber, it is broken up and removed, until the replacement pipe reaches the exitchamber.

These methods are only applicable for existing pipes with sufficient remaining thrustcapacity to withstand the push and pull forces from the jacking machine or pullingdevice.

Pipe Reaming

Pipe reaming is a modified HDD reaming process. A drill string is inserted through theexisting pipe, a reamer is attached to the end of the drill string, with HDD rig beingused to pull the reamer back through the old pipe, breaking it in process.

The reamer has cutting teeth which fragments the pipe which are then carried backwith the drilling fluid and removed. The returning fluid; containing the fragments, caneither be recycled on the surface in a mud recycling system, or retrieved using avacuum truck for disposal. The new pipe, which is attached to the reamer via a swivel

and towing head, is pulled in during the reaming process.

This technique is limited to non-metallic pipeline replacement and is capable ofhandling ground conditions including rock, concrete encasements, service taps, andcollapsed or misaligned pipes.

6.3 When to Apply Pipe Bursting

As part of the feasibility study, the condition of the existing pipe will be determined

prior to the commencement of any PB procedure. If the existing pipe has collapsedthen most bursting procedures will not be suitable or possible. A pipe assessmentreport will assist in determining the most suitable methods of replacing the pipe.

The International Pipe Bursting Association (IPBA) categorizes PB works into three

classifications based on the level of installation difficulty. A general outline of thisclassification is shown in Table 6.1. This table provide parameters that can assist theusers determine if their PB work is routine, challenging or difficult. If at any one time,the combinations of the selected parameters fall into either of the classification, then,the overall classification of the work will be governed by the highest classification.

If the new pipe is significantly larger in diameter than the existing pipe, thereplacement procedure may be considered too difficult or risky. It is important to notonly consider the percentage change in diameter but also the increase in soil volume


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displaced during a PB Works. A TT standard industry practise for PB would recommendthat upsizing of between 0 and 25% is most commonly considered in PB Works.

PARAMETERS

CLASSIFICATION DEPTH OFPIPE (M)

EXISTING PIPEDIAMETER

NEW PIPEDIAMETEROPTIONS

BURSTLENGTH

(M)

A - Routine < 4 DN100 to DN300Size for size to 1up size

< 100

B - Challenging to

Moderately Difficult4 to 6 DN300 to DN500 2 up size 100 to 150

C - Difficult to Extremely

Difficult> 6 DN500 to DN900

3 or more up

sizes> 150

TABLE 6.1: GENERAL PIPE BURSTING CLASSIFICATIONS8

6.3.1 Capabilities

The pipe bursting replacement method is ideal when the pipe quality, performance ordurability of repair is less cost effective than for installing a new pipe. This also appliesto defective pipes that cannot be, rehabilitated by methods such as relining and thereduction in capacity is not an option. Tool, expander and cutters used during PB workare another area that if not properly planned out could affect the success of the PBwork. Table 6.2 shows a list of recommended cutters for pipe bursting work. Factorsthat could influences the selections of these accessories shall include but not limited tonew pipe materials type, depth and profile of pipe alignment, jobsite layout, burstlength, soil conditions. Table 6.3 indicates suitable applications for pipe bursting.


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TYPE OF PIPE

TYPE OF CUTTER

STATIC PNEUMATIC

ROLLERBLADE

LEAD

PIPEBLADE

PLASTIC

PIPEBLADE

BLADED

BURSTINGHEAD

BLADED

BURSTINGHEAD

Cast Iron Pipe 9 9 9

Ductile Iron Pipe 9

Steel Pipes 9 9* 9*

PE/PP Pipes 9 9

PVC Pipes 9 9

Asbestos Cement Pipes 9 9

Lead Pipes 9

Vitrified Clay Pipes 9 9

Concrete/Reinforced

Concrete Pipes 9 9

Glass Reinforced Plastic Pipes 9 9 9

Brick Pipes 9 9

*only thin wall steels pipes without bell and spigot joints

TABLE 6.2: TYPE OF PIPE CUTTER

PIPELINE TYPE NOTES / REMARKS

Sewers Yes

Gas pipelines Grooves in the pipe surface must be documented and

ventilation must be provided to avoid gas pockets

Potable water pipelines YesChemical or industrial pipelines Yes

Pipelines with bends Bends up to 20 degrees can be accommodated overa certain distance

Circular pipes Yes

Noncircular pipes The new pipe must have a circular shape

Pipelines with varying cross sections The new pipe must have the same size

Pipelines with lateral connections Ensure lateral connections connected properly

Pipelines with deformations Yes

Pressure pipelines Yes

TABLE 6.3: PIPE BURSTING APPLICATIONS2

6.3.2 Limitation

The three major types of Pipe Bursting, Pneumatic, Hydraulic, and Static Pipe workwell with a wide variety of fracturable pipe materials and diameters. However, existingpipes materials such as ductile iron and steel are seen as a limitation of the pneumaticPB method.


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General limitations for pipe bursting operations are mentioned below but shall not belimited to:

• Economic aspects as it might not prove cost effective if too many lateralconnections are shallow host pipe compared to open-trench replacement,

• Potential damage to neighbouring utilities and structures if proper identificationand location of the existing utilities and point repairs was not carried out,

• Technical aspects (ability to provide sufficient energy to complete theoperation).2

Unfavourable site conditions for pipe bursting include:

• Saturated expansive soils, or varying soil profiles,

•

Obstructions in the form of completely collapsed pipe,

• Valves, steel clamps or repair bands, point repairs,

• Concrete envelopment,

• Adjacent pipes or utility lines that are very close to the pipe being replaced. The

recommended clearance to parallel pipelines should be greater than 3 times thenew pipe outside diameter,

• Shallow host pipe, within 1m of the surface cover,

• Short pipe bursting distance with too many lateral connections.

6.3.3 Replacement Piping

Most pipe bursting projects, such as gas, water and wastewater lines, utilise fusedlengths of High Density Polyethylene Pipe (HDPE). Hot fusing long segments of pipetogether prior to insertion reduces the likelihood of needing to interrupt the burstingprocess. HDPE also allows pipe insertion into the entry chamber at an angle due to itsflexible nature.

Sections of pipe joined in the insertion chamber should be joined via mechanicalcoupling, electro fusion coupling or a non-shear restraint coupling. All connections

should conform to the manufacturer’ s specifications. 9

It is preferable that all pipe joints have a nominally flush exterior profile to ensure less

frictional resistance during installation. Recent developments have introduced a specialflush-joint for ductile iron pipe, suitable for sewer and potable water applications.

When installing segmented pipe such as steel, concrete, clay or fibreglass, it will benecessary to use a push-pull system. This method requires an additional hydraulic jacking machine in the launching chamber to push the pipe through. This methodprevents the newly installed pipes from being exposed to the high tensile forces. It isalso recommended that lighter coloured pipe is used to facilitate inspection after the

installation.10


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Exterior pipe damage assessment is difficult to carry out and detect once installation iscompleted. Inspection for exterior damage should be carried out prior to installation toensure the integrity of the pipe. Hydrostatic testing should also be performed prior to

installing the pipe to ensure any defects are addressed.

One of the accepted testing technique is to pull out 2 – 7m of pipe and examine it afterinstallation from the receiving chamber as this front section of the pipe tends toreceives the most impact and damage from the installation process. Internal damage

of a replacement pipe should often be revealed via the use of post-CCTV inspection.11

7.0 FRONT END ENGINEERING

7.1 Technical Feasibility

New Pipe New Alignment

Prior to any pipe installation, a feasibility study should be performed to assess thecosts and benefits of installing new pipe using open cut and TT methods.

A detailed survey of the proposed site conditions including existing ground featuresand characteristics should be carried out. The survey should be conducted along theproposed alignment centreline to a width of at least 30m for new installed pipe. Theconditions encountered play a key part in decisions related to new pipeline installation.Key characteristics include earth type, stratification and groundwater conditions, aswell the existing surface infrastructure, including areas occupied by people. Aerialphotographs, if available, can assist greatly with this process.

Consideration of the surface infrastructure is also important since sufficient space and

area has to be allowed all TT and its ancillary equipment, product pipe layout, andpossible drilling fluid support system (if applicable) considerations (including availabilityof a water source and the acceptance of slurry disposal).

In order for an HDD project to be considered technically feasible, it must be able to beperformed with existing tools, equipment and techniques. This means that it must bewithin the current limitations imposed on the process by length of HDD bore, theproduct pipe diameter, and the maximum thrust that can be applied.12

New Pipe Existing Alignment

Technical feasibility considerations for PB will be different, as the replacement method

uses the existing pipeline alignment. When compared to other installation andreplacement rehabilitation methods such as cured-in-place pipe, fold-and-form pipeand sliplining, pipe bursting has the main advantage of being able to replace or upsize

the existing service lines without reducing the current pipe capacity. Specifically, pipeeating is another TT replacement method that can modify the grade of the existingpipe and correct unwanted sags in the existing pipe alignment.

In many instances for waterlines, an open cut replacement may be the preferred

option as the existing pipeline is often shallow and therefore trenching may be acheaper process. Waterlines for housing estates include far many connections thatrequire individual reconnections after the open cut method is completed. However,


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under many conditions pipe bursting has also numerous advantages over the open cutreplacement method.

Some of the possible advantages and benefits of TT include:

• Overall cost savings on reinstalment of all surface infrastructures,

• Social cost benefits by not affecting businesses, residents or customers,

• Reduction of construction wastage,

• Faster and more efficient process,

• Less environmental disturbance,

• Less disruption to surface and local traffic.

7.2 Economic and Social Feasibility

Australasian Society for Trenchless Technologies - Guidelines for Hdd

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