United Kingdom Society for Trenchless Technology: UKSTT - Replacement Techniques

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Replacement Techniques

The following pages describe methods of on-line replacement of existing utility lines including gas pipes, ducts, water pipes, sewers and potentially cables.

• Pipebursting
• Pipe Splitting
• Pipe Eating
• Lead Extraction & Replacement Systems

Schematic supplied by U Mole Limited

Pipebursting

Click here to view all UKSTT Members involved with Pipebursting.

Pipe Bursting is a method of on-line replacement of fracturable pipe usually from excavations 10-200m apart. Extensive proving work by the gas and water industries has demonstrated the feasibility of upsizing gas mains, water mains and sewers. An expanding device which, may be either pneumatic or hydraulic, is introduced into the defective pipeline, shattering the pipe and drawing in the new line behind it. Insertion of short lengths may be made from pits but this involves jointing of the pipeline within the pit. This can be avoided by the use of silt trenches to insert pipe strings. Upsizing from 100mm to 225mm diameter is now well established, and pipes of up to 600mm diameter and greater have been replaced.

Two methods are commonly used as outlined below.

1. Static Bursting (Rod or Winch Systems)

• The pipe to be replaced is exposed and cut out at two points, typically 100 - 120 metres apart in gas/water/ducting applications and 5 - 50 metres in man hole entry applications.
• The hydraulic burster is positioned in the excavation and the rods individually connected and pushed into the old pipe
• Once inserted to the launch pit the bursting tooling is screwed onto the rod and the new pipe connected via a towing head to the rear
• Switched into reverse the hydraulic burster pulls back the rods, bursting head and new pipe. Each rod is unscrewed and removed, or in the case of two-way bursting, fed directly into the next 100 metres of pipe
• On reaching the hydraulic burster the tooling is disconnected from the new pipe and removed

 

 

Schematic Courtesy of U Mole Ltd

 

2. Pneumatic

• The pipe to be replaced is exposed and cut out at two points, typically anything from 5 - 100 metres apart
• A winch cable is pulled into the old pipe with a cobra flexible rod
• Using the cobra flexible rodding, the air supply hoses are pulled through the new pipe to be installed and connected to the compressor and the rear of the cracker
• The new pipe is secured to the rear of the cracker, which is in turn connected to the winch cable and drawn into the launch pit and the air supply turned on
• During the forward progression the winch maintains tension, ensuring that the cracker remains on line with full impact potential whilst overcoming any drag on the new pipe being installed

 

Schematic Courtesy of U Mole Ltd

3. Expandit Pipe Bursting 

• The Expandit system is a true manhole-to-manhole method of pipe bursting, with no need for excavations.
• The 2 manholes are prepared for bursting by the removal of the benching and the two pipe entry points.
• The Expandit head is lowered into the launch manhole, whilst a winch is positioned above the reception manhole.
• The head is then hydraulically expanded & contracted, which bursts the existing pipe, pushing the fragments into the existing pipe bed/surround.
• The head is then jacked forward using segmental pipe, which is machined to suit the size of the manholes.
• As jacking progresses, the winch is used to maintain straight-line stability of the head, and to ensure it stays central within the existing pipe.
• On reaching the reception manhole, the head is disconnected and the benching in the 2 manholes reinstated.

Pictures Courtesy of Perco Engineering Services Ltd

Sketch courtesy of Perco Engineering Services Ltd.

Recent developments have led to a combination of HDD Horizontal Directional Drilling and Pneumatic or Mechanical Impactors being used for certain applications as below.

 

Directional Drilling unit equipped with an air driven Impactor

Schematic Courtesy of B Trac Limited

Pipe Splitting

Click here to view all UKSTT Members involved with Pipe Splitting.

Pipe Splitting is similar in technique to Pipebursting but is used on non-fragmental pipes such as Steel, Ductile Iron or Polyethylene. The technique is generally the same but instead of utilising conical burst head and blade formats the systems use specialist splitting heads designed to cut through the pipe wall, and joints, and expand the existing pipe into the surrounding ground.

Clampburster
Photo courtesy of U Mole Limited

Pipe Eating

Click here to view all UKSTT Members involved with Pipe Eating.

Predominantly used on concrete sewer installations this system allows for size for size replacement and upsizing.

Pipe Eating is an on-line microtunnelled replacement technique. The existing defective pipeline is crushed (or eaten), by the tunnelling machine and removed through the new pipeline. Lateral connections must be disconnected in advance and may be replaced by rider sewers or reconnected by angled drilling.

Photo courtesy of WRc

Lead Extraction & Replacement Systems

Click here to view all UKSTT Members involved with Lead Extraction & Replacement Systems.

Various systems of extraction are used to predominantly replace lead and steel service pipes. Techniques are varied with impact moles and pipe pulling machines - which utilise clamping jaws to extract the existing steel or lead (which have previously inserted with a steel cable) pipes.

All of the systems rely on good strength of the existing material and for the service line to be relatively straight.

Usually the new pipe is towed in behind the old pipe with and expansion cone used to reduce drag or allow upsizing in some cases.

UK Society for Trenchless Technology, 38 Holly Walk, Leamington Spa,
Warwickshire, CV32 4LY, United Kingdom

Telephone: +44 (0)1926 330 935, Fax: +44 (0)1926 330 935, Email: admin@ukstt.org.uk