Pipe Extraction

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TECHNIQUE

Pipe extraction is a trenchless pipe replacement technique that removes existing pipes for disposal while at the same time installing a new replacement PE100 or PE100-RC pipe. There are several systems that have been developed to remove existing pipes while at the same time replacing them with a new PE100 or PE100-RC pipe. All involve pulling out and breaking the existing pipe while simultaneously pulling in the new pipe. The breaking or splitting cone is situated in the excavation and remains static; the old pipe is pulled onto it and broken up for disposal. The technique is used where it is not permitted to leave the fragments of the old pipe in the ground, for example because they are considered to be hazardous waste in some jurisdictions. Upsizing is possible with this method.

Pipe Extraction
Image courtesy: INTERNATIONAL SOCIETY FOR TRENCHLESS TECHNOLOGY

PE100 APPLICATIONS

Water mains.
Gas mains.
Pressure sewers.
Water services (especially lead pipes).
Gas services.

INSTALLATION PROCEDURE

The winch unit/rod puller and reaction plate are installed in the exit pit and the rods are pushed through the pipe to be extracted to the entry pit. These rods pass through the bursting or splitting cone which is located in the exit pit adjacent to the winch (see Figure below).

Pipe Extraction
Image courtesy: KARL WEISS GmbH & Co

At the entry pit the rods are connected to a conical adapter which in turn is connected to the new PE100 pipe string to be pulled in. This adapter is pulled by the rods against the exposed end of the old pipe and, as the winch applies tension through the rods, pulls the old pipe onto the burster cone in the exit pit. The old pipe is broken into fragments in the exit pit and these can be disposed of safely as local regulations require.

The burster cone may be placed in intermediate pits if necessary and moved towards the exit pit each time the new pipe reaches it. This enables longer pulls from a single winch position. Opportunity should be taken at intermediate holes to inspect the condition of the pipe wall to confirm that any surface scratches or defects are less than 10% of the pipe wall thickness. Any defect in excess of 10% must be investigated.

When extracting spigot & socket jointed pipe the direction of extraction is important. It will be considerably more difficult to pull pipe in the direction of the flat face of the joint than in the direction of the conical face. Pulling towards the flat face also increases the risk of pulling soil with the pipe which further increases winch load and may cause significant voids to occur.

Pipe Extraction

PREFERRED PULLING DIRECTION ---->

For gas and water service pipes specialist pipe extraction tools can be used to pull out the existing service pipe and replace it with PE. This is especially useful for removing and replacing lead service pipes in the water supply system. The method can be applied to lead, copper, galvanised iron and PVC service pipes that are continuous and straight. The replacement PE pipe is attached to the old service pipe at one end using a special coupler. The old service pipe is then pulled out with a specialist winch located at the other end of the line and rolled onto a capstan. The method can replace 15-20 metres of service pipe with DN20, 25 or 32 PE pipe. An example is shown below.

Kobus Pipe Puller schematic and with roll of lead service pipe extracted. Images courtesy Kobus Services Ltd.

EQUIPMENT

Main equipment is either a winch or rod puller and reaction plate placed in the exit pit and a hydraulic power pack at the surface or an excavator-mounted winch as shown above. A burster cone placed in the exit pit or in intermediate pits and an adapter cone on the nose of the new PE100 pipe pulled in. Pull rods for extraction. Winch/rod puller capacity ranges from 550 kN to 1250 kN depending on pipe diameter, length of pull, soil type and upsizing.

Pipe Extraction

850 kN rod puller in exit pit.
Image courtesy: KARL WEISS GmbH & Co

Pipe Extraction

Rod puller operator controlling extraction operation from surface. Note exit pit size and location of hydraulic power pack.
Image courtesy: KARL WEISS GmbH & Co

PRACTICALITIES

Pipe materials replaced need to be brittle. Cast iron and asbestos cement are most commonly replaced using this method.

Excavations are needed at each service connection. Services must be disconnected from the main prior to replacement and reconnected to the PE100 pipe afterwards. These intermediate excavations may be used to place the burster cone so that a longer length of pipe can be pulled from a single winch location.

Not suitable for location where other services are in close proximity to main especially if upsizing.

Not suitable for mains with bends and other fittings e.g. syphons.

Typical output rates for pipe extraction are in the range 60 – 90 metres/day.

Soil Types and their effects

Hard rock. (except if upsizing) Soft rock. Clay. Silt. Sand. Fine gravel. Coarse gravel. Boulders.

Diameter, pressure and Length Range

Refer to data input spreadsheet.

EXCAVATIONS

Typical exit pit size is 2.5m. long x 1.2m. wide. Depth is 0.5m. below pipe invert. Entry pit width and depth as exit pit. Length depends on depth. For the Kobus pipe puller the pit size is up to 1m x 1m and depth up to 1m depending on the depth of the pipe to be removed.

DESIGN, SPECIFICATION & PLANNING

Design

Fluid/hydraulic design for capacity of new pipeline to determine diameter needed.
Select SDR based on operating pressure
Check tension load capacity during pull-in

Specification

Specify maximum allowable tensile load during pull-in based on pipe manufacturer’s recommendations and method of load measurement.
Specify end fittings and service connection details.

Planning

Pre-CCTV recorded survey of the existing pipe is recommended to identify any obstructions
Pit locations.
Straight runs of pipe only – no bends and other fittings e.g. syphons.
Proximity of other utilities and services. This method can cause some ground movement especially in cohesive soils.
Containment and disposal of asbestos cement pipe fragments in accordance with local regulations.

This method applies tension to the PE100 pipe during installation. The tensile load on the pipe during installation must be calculated to establish whether it exceeds the maximum allowable load. Pipe manufacturers can advise on the allowable loads. If the calculation shows that the maximum permissible load may be exceeded then it may be necessary to increase the capacity of the PE100 pipe by increasing its thickness. This will require a check of ID and OD to ensure that flow capacity and external clearances are still adequate.

HEALTH, SAFETY & ENVIRONMENT

Winch/rod puller operation must be from a control unit at the surface, for two reasons.

1. The system works with high tension on the pulling rods. No personnel should be in the exit pit where the winch/rod puller is located while the winch/rod puller is in operation and under tension.

2. If replacing asbestos cement pipe special measures must be taken in accordance with local regulations to contain and dispose of the pipe fragments and any fibres so that fibres are not released to the atmosphere. No personnel should enter the pit unless wearing suitable personal protection equipment.

Pipe Extraction
Rod puller operator controlling extraction operation from surface.
Image courtesy: KARL WEISS GmbH & Co

STANDARDS & CODES OF PRACTICE

DVGW Hinweis W 396: “Demolition, Rehabilitation and Installation Works on Asbestos Cement Water Mains”, December 2004.

DVGW Arbeitsblatt GW 322: Trenchless Replacement of Gas and Water Mains Part 1: Jacking/Extraction Methods – Requirements – Quality Assurance – Testing; October 2003.