Guidelines for the application of pipe bursting

Pipe replacement by open trenching involves traffic impairment, noise- and emission pollution when breaking open the surface. Also there is a risk of surrounding underground pipe damage, soil and groundwater intervention and higher storage, transport and soil removal costs. These drawbacks can be almost completely avoided by replacing pipes using trenchless technology.

According to estimates of Advantica, the pipe bursting method has become the most widely applied trenchless pipe replacement method with more than 50,000 km worldwide. With the pipe bursting method, the defective or underdimensioned pipe is cracked with a burst head and then displaced into the surrounding soil. This creates space for the new pipe directly proceeding, of same or greater diameter. The pipe bursting technique allows the replacement of defective pipelines in the same path without any substantial influences on soil and groundwater. Open trenching which requires the breaking up and repairing of valuable surfaces is thereby almost entirely eliminated. In addition, this eco-friendly technique helps to cut down costs considerably. The pipe bursting distances usually have a length of approx. 100 - 200 m. Pipe bursting can be carried out from pit to pit, from pit to manhole (sewer) and from manhole to manhole (sewer).

In general, there are two methods to choose from:

• Hydraulically operated static pipe bursting with ladder shaped Quicklock rods (Figure 1)
• Pneumatically operated dynamic pipe bursting with piercing tools or rammers.

The following phases are essential for the successful performance of pipe bursting:

1. Planning phase
2. Preparation phase
3. Performance phase
4. Completion phase. 

1. Planning phase

The basis for careful planning is

• meticulous inspection of the existing host pipe and joints condition (including CCTV),
• survey of existing pipes and other underground structures in the proximity of the host pipe,
• ground survey in the periphery of the host pipe and
• determination of the new pipe and joint material and their dimensions (same diameter or larger).

From this initial information, the projecting engineer should be able to determine whether or not pipe bursting can be applied. If the answer is yes, the next step is the selection of a suitable pipe bursting sub-technique (e.g. dynamic/pneumatic or static bursting). For simplification and a systematic approach for the preparations, it is advantageous to work with checklists at this stage.

1.1 Host pipe
A careful inspection of the host pipe proposed for replacement should include:

1.1.1 Pressure pipes

• Material and any changes of material
• Nominal diameter and any changes of diameter
• Replacement length
• Depth of ground cover (distance between the crown of the [new] pipe and the ground surface or river bed)
• Distance between the host pipe and adjacent underground structures, parallel or crossing pipes in close proximity
• Changes in pipe line direction, horizontally or vertically offset pipes
• Joints and connections
• Fittings, pipe clamps, valves, syphons, etc.
• Types of damages, i.e. of pressure pipes, particularly incrustations, deposits, etc.
• Obstacles in the pipe bedding (e.g. concrete surrounding host pipe)
• Space available for crew, material and equipment, etc.

1.1.2 Sewage pipes

• Material and any changes of the material
• Nominal diameter and any changes of the diameter
• Replacement length
• Depth of ground cover (distance between the crown of the [new] pipe and the ground surface or river bed)
• Distance between the host pipe and underground structures, parallel or crossing pipes in close proximity
• Changes in pipe line direction, horizontally or vertically offset pipes, bends
• Laterals and lateral joints (angles, location, depth, function, etc.)
• Types of damages, e.g. cracks, fractures, breakages, sags, slab-outs (missing pipe fragments), deformations, root infestations, pipe collapses, blockage debris, etc. (CCTV inspection necessary)
• Soil conditions, groundwater level
• Obstacles in the pipe bedding (e.g. concrete surrounding host pipe, old manholes, foundations, carriers, sheet pilings, sheeting material, etc.)
• Host pipe gradient
• Space available for crew, material and equipment, etc.

1.2 New pipe
The following minimum criteria must be observed when selecting a new pipe to be installed by pipe bursting:

• Material, maximum admissible strength
• Nominal diameter, hydraulic capacity
• Type of pipe joints
• Surface cover
• Short pipe/long pipe/pipe in coils or on drums, etc.

1.3 Survey of the underground conditions in the area of the host pipe
The contractor should always be aware of existing pipes or other structures when working underground. This could include:

• Gas- or water mains and service pipes
• Electric cables
• Sewage mains and laterals
• Telecommunication lines
• District heating systems
• Traffic guidance systems
• Pipes for military purposes, e.g. fuel lines
• Other pipes, e.g. pipes for special chemicals, oil and gas pipelines, pneumatic post systems, etc.

According to reports [1], pipe damage in Germany amounts to 200 million Euro per year. 93% of these damages occured despite having information prior to the excavation work. 79% of the damages were caused by various kinds of excavation machines. 55% of all damages from these accident statistics, occurred out of carelessness. Therefore, the qualification demands on the construction companies regarding pre-construction survey and safeguarding responsibilities are very high. The construction company is obliged to obtain the necessary degree of information concerning existing pipes and cables from the authorities who map and record reliable documented data. In several countries contractors can rely on “One-Call” services. In this case, contractors receive all relevant information about existing pipes and cables from one source. However, if the position of the existing lines are unknown or indeterminate, the contractor must find them out by digging trial holes and/or using geophysical location methods

One Call Services are in place in many of the 50 USA states. There are some states that do not have this desireable service, (example: Hawaii) so the contractors in Hawaii must individually contact each utility to research a given work area. Even when the one call system does the locating, the contractor is still responsible for accurately locating and sometimes exposing potential utility conflicts. The individual utilities are responsible for accurately locating their facilities.

According to legal (e.g. German civil code, workers protection law), contractual (e.g. German construction contract procedures) and technical regulations (e.g. DVGW – German Technical and Scientific Association for Gas and Water, DWA – German Association for Water, Wastewater and Waste, DIN – German Institute for Standardisation, etc.), the contractor is obliged to carry out extensive surveys.

In some countries it is not clear as to which rules and regulations contractors are obliged to carry out for surveying underground pipes, cables and structures. In those cases it is advisable to clarify each open point in an individual contract.

On the other hand, pipe or cable network owners are obliged to provide the information. Normally, the contractor is informed by the municipal authority about the networks which must be considered during the pipe bursting project. The contractor has to contact the network owners, who are obliged to hand out the required information. A job site inspection, carried out by all parties involved, is strongly recommended.

Sometimes residents living in the area are able to help with information (however, this should not be solely relied upon). Many companies also benefit from experience and data gained during former projects in the same area.

A pipe bursting project is always applied to host pipes. Therefore, one may assume that these existing pipes are embedded in refill material inside a previously excavated trench. But this doesn’t necessarily mean that the soil surrounding the pipe is easily displaceable. This becomes even more unlikely, the longer the pipe has been laid in the ground. In the course of time, an exchange of fine grain particles between backfill inside the trench and the undisturbed soil at both sides of the trench takes place due to material migration. As a result, the soil may consolidate above the host pipe and at its sides. Some soils are well displaceable, with almost no subsequent settlement. These soil conditions are ideal for pipe installation, particularly, when upsizing the pipe diameter in the future. Initial backfills, still close to their original condition, for instance, are suitable soils, and so are easily displaceable cohesive and non-cohesive soils.

Other, mostly cohesive soils, are well displaceable but quickly settle, causing high surface friction of the new pipe. For example, the displacement of extremely dense, groundwater carrying sandy soils or densely packed clay is very difficult. Soils like quick sands are not stable and create extreme surface friction. In such cases, friction reducing measures like Bentonite lubrication should be considered. Beyond this, special measures to prevent these soils flowing into pits become necessary when planning the shoring of pits. Bursting projects e.g. in gravel are quite easy to accomplish. When pipe bursting in rocky undergrounds the size of the expander and the width of the former trench (host pipe diameter) have to be taken into account (Will the expander fit into the former host pipe trench?). If the soil beneath the pipe bottom is rocky, the level of the new pipe compared to the level of the host pipe may rise during pipe bursting.

The period in which the host pipe was initially installed also plays an important role. Example: Remembering the post-war years in Europe, we are aware of the fact that the backfill that was used at those times was any material that was available. Many pipes are embedded in rough rubble, building debris or iron and steelworks slag.

1.4 Bidding process and award of contract
When all information about the host pipe and soil conditions are available and it is feasible to actually install the selected new pipe applying dynamic pipe cracking or static pipe bursting, the principal (network owner) usually first invites bids to be submitted before awarding the pipe bursting contract.

First, the bids are entered, followed by the submission and finally awarding the project comprising the underground engineering and pipe bursting works. Unfortunately, often the contracts are not given to those who offer the best price/performance ratio, particularly considering quality aspects. Regretfully, in most cases the bidder with the lowest price is awarded the contract. However, shouldn’t the principals focus on qualifications, experience and reliability of the contracting company when awarding trenchless technology projects (ask for references, if in doubt)? Also ask about the quality of the equipment to be used.

Principals (network owners) should check the qualification certificates of the contracting companies very closely. In many countries, however, there is no specific contracting company qualification procedure available. Here are some examples:

• In the UK, there is specific requirement regarding a certification, however, manufacturers like TTUK Ltd. offer assessment and special operator training for pipe bursting. Successful participants are awarded City & Guilds certification. This qualification forms part of the City & Guilds 5831 Utilities Operations Scheme – Trenchless Technology. More and more network owners insist on contracting companies having trained and certified personnel.
• In Germany: Replacing gas and water pressure pipes a DVGW certification in the supplementary certification group GN 3 or AGN 3 according to DVGW GW 301 (A) „Qualifikationskriterien für Rohrleitungsbauunternehmen“ (Qualification criteria for pipe line installation contractors) or GW 302 (A) „Qualifikationskriterien an Unternehmen für grabenlose Neulegung und Rehabilitation von nicht in Betrieb befindlichen Rohrleitungen“ (Qualification criteria for contractors of trenchless new installations and renewal of pipes out of service). Replacing sewer pipes requires a certificate according to Gütesicherung (quality assurance) RAL-GZ 961 of the Gütegemeinschaft „Herstellung und Instandhaltung von Abwasserleitungen und -kanälen e.V.“ (Quality association “Installation and maintenance of sewer mains and laterals”)
• In the USA, requirements run the full spectrum from no qualifications to very detailed experience and qualification statements, references to past similar projects and acknowledgment of licensing by Advantica (not in effect any longer). The requirements are usually local and are not mandated by the federal or state governments.

Just as important as the existence of certificates are

• a well trained and experienced crew (evidence of continued education at regular intervals) and
• holding suitable machine technology.

2. Preparation phase

As soon as a construction company has been awarded the contract to carry out the pipe bursting job, preparations for the replacement project can commence. A good co-operation between principal (network owner) and contractor, free of any doubts, is important right from the beginning.

2.1 Selecting the pipe bursting equipment
Basis for the selection of a pipe bursting rig or hammer is the new pipe diameter in relation to the host pipe diameter. Will the replacement be size-for-size or has the host pipe to be upsized? The required performance of the machine (Table 1) is the result of these considerations. The selection of the dimensioning of the new pipe takes place according to the relevant regulations. It is important, that the loads affecting the new pipe during installation (pipe bursting process), are also taken into account.

Many years of experience prove the fact that upsizing an existing host pipe by one or two nominal diameter sizes is common practice. Up-sizing by more than two nominal diameter grades demands a higher degree of experience. In this case, a machine of a higher pulling capacity should be used. Can the new pipe be upsized at all, and if so, up to which degree can it be upsized? The answers depend on the predominant soil conditions, the available depth of ground cover, the space between the new pipe and other pipes and cables parallel or crossing and the width of the original pipe trench. The dimensioning of a sufficient overcut (clearance) is also essential (Figure 2). The required outer diameter of the expander results from the largest outer diameter of the new pipe (when installing ductile iron pipes for example, this is the outer diameter of the pipe joints) and the required clearance (see Figure 2). The clearance is the annular gap which is generated when an expander with a larger outer diameter than the new pipe outer diameter is used. Normally, the clearance should make up 10 to 30% of the new pipe outer diameter in order to prevent the fragmented host pipe shards from getting jammed. This clearance is smaller when calibre pipe bursting or the Tight-In-Pipe method is applied. Soils with a high cohesion may require a larger clearance. When working in these sticky soils, pumping clear water or water mixed with some soft soap into the annulus should also help to reduce surface friction. With a suitable lubricant, surface friction can also be reduced in loose soils, for instance if Bentonite slurry is pumped into the annulus.

2.2 Determination of the distance to the surface and to existing pipes and structures
After having determined the dimensions of the new pipes and the expander, the upsize coefficient (Figure 2) is determined. Upsize coefficient indicates the difference between the outer diameter of the expander minus the internal diameter of the existing host pipe.

The upsize coefficient helps to calculate the necessary minimum distance to adjacent existing pipes and structures and the required depth of cover.
Example: Internal diameter of the host pipe 150 mm (6"), outer diameter of the expander 225 mm (9") to install new pipe outer diameter 200 mm (8"): This results in the upsize coefficient: 225 – 150 = 75 mm (9" – 6" = 3").

Depth of cover: To prevent the surface from heaving or settling, the depth of cover should be at least ten times the upsize coefficient (as a guide formula). Depending on soil conditions, a larger depth of cover may become necessary in the individual case. In the above example, the depth of ground cover, therefore, should be 10 x 75 mm = 750 mm (10 x 3" = 30").

Independent of the depth of cover, the installation depth of the host pipe influences the choice of pipe bursting equipment, because with increasing depth

• the surface friction of the new pipe increases,
• upsizing by several nominal diameters becomes more difficult,
• the achievable pipe bursting lengths become shorter.

On the other hand, increasing installation depths reduce the risk of ground heaving or settling (see above) and potential damage to existing pipes and structures within the vicinity of the pipe bursting area.

Distance to adjacent pipes (parallel): The minimum distance to adjacent pipes depends on soil conditions (coherence and compressibility in the first place) and the type of adjacent pipes and structures. In cohesive grounds, the clear distance to parallel pipes should be at least three times the upsize coefficient, but never less than 40 cm (16"). In the example above, the clear distance is calculated as follows: 3 x 75 mm = 225 mm < 400 mm (3 x 3" = 9" < 16"). Thus, the minimum distance should be 40 cm (16"). When bursting host pipes DN 50 to 150 (2" to 6") in cohesive soil the minimum clear distance to parallel pipes may be reduced to 30 cm (12") if the material of the adjacent pipe is not brittle and fragile but less susceptible to breakage.

In non-cohesive soils (e.g. gravel/sand), minimum distances to other supply and sewage pipes have to be studied very carefully with regard to risk of breakage. If the adjacent pipes are brittle and fragile (e.g. clay, cast iron), the smallest distance should be no shorter than five times the upsize coefficient, the minimum is 40 cm (16"). If we look at our example, the minimum distance is calculated as follows: 5 x 75 mm = 375 mm < 400 mm (5 x 3" = 15" < 16"). Therefore, the minimum distance should be 40 cm (16").

If in sporadic lengths the distance to adjacent and crossing pipes is critical it is advisable to observe these converging areas by opening small pits by means of manual trial holes. 

2.3 Determination of individual replacement lengths and launch and exit pit positions
After having determined the required capacity of the pipe bursting rig or hammer and making sure that soil conditions and the distances to existing pipes and structures allow the installation of the desired new pipe, the next step is to determine the individual replacement lengths and the position of the required launch and exit pits.

The feasible pipe bursting section length depends on the upsizing degree, diameter and the type of new pipe (Table 2 and Table 3). The soil conditions also play a crucial role.

Longer replacement sections are feasible under advantageous conditions. Generally, the application of lubricants like Bentonite slurry or special polymers may also allow the installation of longer pipe sections.

It is always practical to arrange the pits within the area of the lateral resp. service connections or manholes. This minimises the number of additional pits as pits for disconnection or re-connection of service lines or laterals which are generally required anyway. The pits should be positioned in a way that allows to burst in either direction from one machine pit (exit pit). The bursting rig or alternatively the cable winch only needs to be turned around 180° to face in the corresponding direction. Ultimately, the site layout conditions are decided for the optimal arrangement of the working pits. When applying static pipe bursting, the rods can be simultaneously pushed into the next section while bursting the first section (Commonly known as Two Way Bursting – TWB). The rig is then only turned around by 180° for the second bursting section.

After all the required information has been obtained, the complete job is costed and the work planned section by section. Service connections or laterals are located from the existing pipe network drawings. Amongst others, these project design methodology plans should contain:

a) Pressure mains and service pipes

• Method (static or dynamic pipe bursting)
• Description of renewable sections with consecutive numbering
• Section lengths
• Nominal diameter of the host and new pipe
• Material of the host and new pipe
• Soil type/soil properties
• Any method-specific information
• Any existing crossing or parallel pipes or structures
• Any changes in pipe line direction, horizontally or vertically offset pipes,
• Any existing service connections including connections out of use
• Access and excavation permits
• Coordination with any other construction projects, etc. 

b) Sewer mains and laterals

• Method (static or dynamic pipe bursting)
• Description of renewable sections with consecutive numbering
• Section lengths
• Nominal diameters of the host and new pipe
• Material of the host and new pipe
• Soil type/soil properties
• Any method-specific information
• Any existing crossing or parallel pipes or structures
• Any changes in pipe line direction, horizontally or vertically offset pipe
• Any existing laterals including laterals out of use
• Groundwater conditions, including groundwater control measures
• Mean sea level (MSL) of existing structures and connections
• Level and inclination of host pipe . Flow direction and gradient
• Hydraulic conditions
• Overpumping or bypass to ensure continued effluent disposal
• Access and excavation permits
• Coordination with any other construction projects, etc. 

The design and methodology plans must be readily available and accessible at all times for the construction company before the project is started. The contractor, in turn, must verify all data according to the actual conditions found on the jobsite.

2.4 Equipment set-up on site
After all relevant details have been defined in the planning phase, it is the time to carry out the actual pipe bursting process. All preparations and set-up must be well planned in all details and in good time. Many questions should be clarified beforehand in order to avoid adverse effects, difficulties and delays. The arrangements on the jobsite should guarantee a safe operational performance without general disturbance. Examples:

• What kind of permits have to be obtained and for what duration? Which authorities are in charge? Who is responsible? Is it necessary to heed any special regional or environmental regulations (i.e. permitted working times, pit regulations or demands by residents)?
• Which information has to be given to the local residents?
• How are the traffic conditions on the jobsite? What measures must be taken to secure and regulate traffic? Is the jobsite easily accessible?
• What kind of machinery, equipment and material is needed? Are the machines and equipment ready and reserved for operation on the planned date? Will all required materials (i.e. backfill for the working pits) be delivered on time?
• Are there any space restrictions? Is the available storage space sufficient? Particularly within the pit area? Where can the Power Pack units be stored? Are the supply hoses long enough? Where can the bursting rod boxes be stored, if applicable?
• Where are convenient storage conditions? Where can the product pipes be stored? How are they laid out?
• What kind of bursting tools, expanders and pipe pullers are intended to be used? Are they suitable and in working order? Are alternative tools also available on site?
• Is there any support personnel and/or are lifting devices available for transporting heavy parts (e.g. like expanders)?
• How can water and electricity be provided if the need arises?
• Is it necessary to take groundwater control measures?
• Are all documents concerning ground investigations available, have all existing pipes and structures been recorded and marked? Are further obstacles to be expected? Are the complete jobsite drawings available (e.g. installation plans, etc.)?
• Which are the reference points for the subsequent mapping of the new pipe?, etc.

2.5 Working pits
After the jobsite is finally set up, the working pits (Exit pit = machine pit, intermediate pits if required, starting pit = pipe launch pit) are prepared and shored in accordance to the existing regulations. Examples:

• UK: Health and safety in excavations ´Be safe and sure´ HSG185 (which comes under the construction regulations ´Managing Construction for Health and Safety ´)
• Germany: DIN 4124 and the relevant accident prevention regulations
• USA: OSHA, State and local regulations, shoring over a certain depth, 6 m (20’) or more is required to be Certified by a structural engineer.

Intermediate pits may become necessary as soon as bends, laterals, service pipes and other known obstacles are expected to obstruct the pipe bursting process, but also when new connections need to be integrated. When working in areas with groundwater, the working pits must be secured to prevent any water ingress.

Usually, the depth of the working pits is determined by the level of the host pipe. Depending on the applied equipment, however, slightly deeper exit (machine) pits may be required. Otherwise the dimensions of the pits are orientated by the required working space (i.e. the length of the bursting tool for starting and recovering, the rod length or minimal bending radius of the new pipes, etc.) or the local site conditions. The working pit length can be shortened for PE pipes, if it is possible to lift the pipe string by the depth of the host pipe above ground (considering the minimum bending radius of the PE pipe). Table 4 gives guidance about the length of the exit (machine) pit for static pipe bursting.

2.6 Taking the host pipe out of service
After the working pits have been prepared, the pipe replacement section must be separated from the network and the service pipes or laterals and any possibly existing pipe tees in a working pit. They have to be cut back sufficiently to avoid damage during the pipe bursting process.

2.6.1 Pressure pipes
For gas and water pipes, disconnection and taking out of service has to be carried out according to the relevant regulations for gas and water pipe installation/maintenance. Should the need arise, a substitute supply must be arranged. If the host pipe is asbestos-cement specific personnel safety measures have to be considered when taking the pipe out of service.

2.6.2 Sewage pipes
Quite often for the renewal section and the laterals a substitute effluent disposal measure must be installed. The effluent disposal can be maintained by over pumping or bypassing or even blocking the upstream pipe during the downstream pipe bursting process.

2.7 Preparing the pipe bursting equipment
2.7.1 Pipe bursting equipment
Every day before starting to operate, the bursting equipment must be checked regarding its completeness and maintenance condition. This is valid for all jobsite safety facilities and lubricants as well as consumables. Even before the equipment is transported to the jobsite, all important parameters should be checked by using a check list and the instructions and recommendations given by the manufacturer.

2.7.2 Dimensioning of the overload protection
In some countries (e.g. Spain, Germany) the pulling forces directly affecting the new pipe must be monitored from the front end of the new pipe during the entire static pipe bursting process. In the US Gas industry, it is normal to pull new pipe with some sort of a “weak link”. Water and Sewer projects have not required this, yet. Chart recorders, data loggers are going to become more noticeable. In several other countries this quality control procedure is expected to be standardised in the near future. However, tensile force measurement is not possible with the dynamic pipe cracking method. Therefore, the use of an alternative overload in-line pipeline protection (“weak link”) can be used for that purpose (also for static pipe bursting), whereby the pipe breaks before the permissible tensile stress of the pipe rises above manufacturer specified load. The cross-sectional area of the overload pipe protection for PE-pipes, for instance, must not exceed a maximum of 40% of the cross-sectional area of the new pipe.

Example:

• New pipe PE 100, OD = 200 mm (8"), ID = 163.2 mm (6.4"), wall thickness s = 18.2 mm (0.72") = SDR 11
• Cross-sectional area A of the new pipe = 10.366 mm² (16.04"²)
• Cross-sectional area Amax of the overload protection = 0.40 · 10.366 = 4.146 mm² (6.43"²)
  • by slots spread evenly over the circumference of the pipe (Attention: to prevent dirt from entering!) or
  • by using a pipe section (Attention: must be same material!) with a smaller wall thickness. In our example, one would take a PE pipe OD 200 mm (8") SDR 33 with a wall thickness of 6.2 mm / 0.24" (A = 3.773 mm² / 5.85"² < 4.146 mm² / 6.43"²). A PE pipe section, turned-out internally, can also be used as another alternative.

The overload protection must be at least as long as the outer diameter of the new pipe (L = OD) and shall be placed completely within the expander.

2.8 Incoming control of the new pipe material
The specifications of the new pipe material to be installed must be available on site even before the material is delivered. Upon delivery, the specifications must be immediately compared with the information printed on the new pipes. A visual inspection of the delivered material is absolutely necessary in order to make sure the pipes are not damaged. Faulty pipe and/or damaged surface coating material should never be installed. However, some surface spot repairs may be permissible.

2.9 Obstacles and cleaning
If the result of the inspection of the host pipe shows obstacles that might affect or aggravate the pipe bursting process, these must be removed before the process starts. Reduction of the host pipe profile due to incrustation, etc. needs no correction, as long as there is enough space to pull in a winch cable or push in the bursting rods.

It may become necessary, however, to clean the host pipe, if there is a risk of freeing substances which are hazardous from an environmental point of view (e.g. in some places the contents of gas pipes, tar, creosotes, stabilising agent residues, phenolic dusts). In such cases, cleaning must be performed as carefully as possible to avoid the release of these substances. Keep an eye on condensate collectors and extenders.

Any known concrete beddings and partial or complete concrete casings surrounding the host pipe which prevent the use of pipe bursting are to be removed by using excavations.

3. Performance phase (pipe bursting process and pipe installation)

The construction company generates a detailed work preparation plan together with an operating schedule. All relevant working steps should be available as operation and working instructions and all well-known to the site crew. Contracting companies solely specialised in pipe bursting are often employed for carrying out the actual pipe bursting process. Work preparation, excavation and connection of the new pipe into the existing network are not necessarily carried out by these companies. The principal and also the main contractor should definitely direct their attention to the qualifications, experience and reliability of these specialist bursting companies.

Additional to conventional daily job site reports the pipe bursting process is documented in a separate report. This file is finally passed on to the principal, together with all the other files documenting the proper installation of the new pipe.

Having prepared the working pits and disconnecting the host pipe from the network, the pipe bursting equipment can be installed:

• Static pipe bursting: First, the bursting rig is safely installed in the machine pit (Figure 3) and fixed against the reacting forces. If the rig has a telescopic pipe recovery frame, this remains completely jacked-in during the bursting process. Assisted by a guide rod, the quick-lock rods are then pushed into the host pipe (Figure 4).
• Dynamic pipe cracking: Before dynamic pipe cracking can commence, the constant tension hydraulic twin capstan cable winch has to be safely installed in the exit pit or manhole and fixed against the reacting forces. Then the winch cable is pulled in to the host pipe using a flexible fibre rod. 

Simultaneously, the new pipe string is prepared at the starting pit end. The extent of these works depends on the pipe material and the available space (i.e. launch pit or manhole). Any PE or steel pipe welding (Figure 5) must be carried out by skilled and certified welders only. The external welding beads of welded PE pipes should be removed, the same goes for internal welding beads of sewer pipes.

When welding a PE pipe with a protective coating, the protective coating in the area of the welding seam must be removed first to be restored after the pipe has cooled down (Figure 6).

The gap between the female and male end of ductile iron joints is to be protected from dirt by a jacket or collar. Damage to the outer protective layer is to be avoided by means of a sheet steel protective cone which is attached after the pipe assembly (Figure 7).

When using pipes with plug-in connections, i.e. PE, PP, PVC, GRP or VCP, it must be ensured that their bell-and-spigot joints cannot come loose. Therefore, these pipes are pushed, not pulled as follows:

• by utilising QuickLock rods with hydraulic tensioner “Burstfix” (Figure 8), for static pipe bursting;
• by utilising a chain with hydraulic tensioner “Spannfix”, for dynamic pipe cracking,
• by utilizing restrained joint pipe such as Ductile Iron, example; TR Flex Joint (US Pipe & Foundry). This allows for pulling instead of pushing the column of new pipe. Other restrained joints for PVC is Certainteed’s CertaLok as an example.

Generally, the new pipe must be connected to the pipe pulling adapter and the expander in a way that avoids ingress of dirt into the new pipe. In case of pulling in PE pipes with a protective coating it must be made sure that the coating at the front of the new pipe cannot become loose or be peeled off during the pipe bursting process. This area should always lie safely within the expander.

The joints of the new pipes should always be visually checked before pulling the pipes in. Coatings of metal pipes should also be tested to be on the safe side.

After the winch cable and bursting hammer respectively bursting head and QuickLock rods have been connected to the new pipe string, the bursting procedure and the simultaneous pipe pulling can begin. Whenever long pipe strings are installed, great care must be taken to avoid disruption of traffic on the roads. The pipe string should slide on rollers laid on the road surface in order to protect the outer coating from damage. When entering the working pit and the underground, or whenever sliding over sharp edges, the new pipe must be protected by means of deflection rollers or lead-in funnels. 

The results of site investigation, e.g. with reference to the position of existing pipes and structures, must now be carefully observed. The damage-free installation of the new pipe has highest priority (slight damages of the protective coating of PE pipes with protective coatings is not considered to be a defect as such, as long as the actual core pipe is without damage!). Manufacturer’s instructions are to be adhered to. When travelling through working pits within the area of critical distances to neighbouring pipes and structures, particular care must be taken. During the bursting operation, the operater should maintain constant contact with his colleagues at the launch and intermediate pits via radio equipment. Fragmented shards created by the bursting action in intermediate pits must immediately be removed, otherwise they might be pushed back into the soil.

A straight-lined course of the host pipe is an advantage for the bursting process. But bends and curves can also be followed up to a certain degree. The burstable bends depend upon the bursting tool, expander or bursting rods employed, but also on the permissible bending radius of the new pipe string and the permissible angle of the single joints (for pipes with plug-in joints). If Quick- Lock rods are being used, quite significant bends (depending on the rod dimensions, from 35 m radius on) can be driven through, due to the flexibility of the joints. [2] report of 11° bends, driven under tensile load. While [3] also describes considerable bends driven through with these rods (Figure 9).

All relevant process steps should be recorded. In several countries the relevant standards require this anyway. In case of deviations from the given instructions, the bursting process must be interrupted in order to discuss further actions with the site engineer and the representative of the principal. Improper overloading of the new pipe subject to tensile stress (due to friction, the deadweight of the pipe and changes in direction) must be prevented. This can take place by continual measurement of the tensile forces acting on the new pipe during installation, the data is subsequently printed (tensile force logger); another option is the use of a predetermined breaking piece. Lubrication of the new pipe can reduce the pipe surface friction along with the reduction of the required tensile force when upsizing by several nominal diameters and / or in cohesive or gravelly soils.

The pulling process is interrupted for a short time as soon as the bursting tool arrives at the exit pit shoring in front of the bursting rig to allow extension of the telescopic frame (Figure 10). This is a hydraulic operation via remote control, rapid and safe for the operator. The support plate is then removed, the bursting tool is pulled into the pit and can be recovered from there. The expander and the new pipe are then also pulled into the exit pit, one after the other, and the bursting operation is complete.

4. Completing phase

4.1 Tests/Inspection
On recovery of the bursting equipment, the required inspections can now take place. The exact kind of visual and technical tests and inspections to be carried out and recorded depends on the type of pipe line installed. The bare pipe sections lying exposed in the pits, at least every 100 m (329 ft), should always be visually examined for possible deformation or damage, no matter what kind of pipe has been installed. A CCTV inspection is also an option, if required.

Regarding durability and requirements on the new pipe, pipes replaced by pipe bursting are to be put at least on the same level as those being replaced by open trench methods. Leak tests and pressure tests can therefore be carried out and recorded according to the criteria of the pipes installed by open trench methods, in conformity with the relevant technical standards valid in the different countries.

• Pressure pipes: Before the pipe can be put into service (again) a pressure test according to the local regulations is usually obligatory.
• Sewage pipes: Visual inspection (CCTV) and a leak test according to the local regulations must be performed.

4.2 Net integration
If the testing and inspecting of the renewed pipe ends with satisfactory results, the pipe must now be re-integrated into the existing pipe network, the service connections and laterals which had been disconnected for pipe bursting can be re-connected. This has to be done in accordance with the relevant technical standards valid in the different countries.

• Pressure pipes: Integration and putting the renewed pipe section back into service is executed according to the local gas and water regulations.
• Sewage Pipes: The integration of the renewed sewer pipe into the manhole must be absolutely water tight. Laterals are reconnected in working pits. If the replacement method was close fit pipe bursting, laterals can be re-connected by means of robotic technology, provided the new sewer main is minimum DN 200.

4.3 Restoring the ground surface
The final steps of a pipe bursting job are refilling the working pits and restoring the original state of the ground surface. (Note: The new pipe that is exposed in launching, receiving or other pits must be carefully backfilled and compacted to prevent deflection of the pipe. This usually is revealed by CCTV inspection.) These final tasks must also be performed strictly by professionals and to the local regulations if not, damage like ground settlement may occur. This could unfairly be blamed on the pipe bursting method. It goes without saying that the jobsite has to be left in a perfectly clean and orderly condition.

5. Quantity measuring, final account, liability

At the end of the pipe renewal, the various job data along with all stipulated documents and reports necessary for the service acceptance are passed on to the principal. The liability period starts on the day the acceptance report is signed (Attention: This may be different from country to country). Finally, the data of the newly installed pipe is downloaded into the database of the utility owner.

Summary

Pipe bursting offers a real technical and cost-effective alternative not only compared to open trenching methods, but also among other trenchless rehabilitation methods. The challenging operations of the past have lead to a perfected process- and machine technology. The technology already exists for a long time and is the most applied trenchless replacement method worldwide.

References

[1] Weckenbrock, P.: Baggerschadenprävention [Prevention of excavator damage], Vortragsunterlage GAT 2004, Frankfurt

[2] Emmerich, P., Schmidt, R.: Erneuerung einer Ortsnetzleitung im Berstlining-Verfahren [Renewal of a local net line with the pipe bursting method], FGR Gussrohrtechnik issue 39, 2005

[3] Schill, J.: Bursting around the bend, Underground Construction, October 2004

[4] Gardener, N., Rameil, M.: Guidelines for the Use of Pipe Bursting: Pipe bursting method for trenchless replacement of cast iron and ductile steel pipes, No Dig International Conference, Hamburg 2004

[5] www.nodig-construction.com