Replacement techniques of existing utility lines including gas pipes, ducts, water pipes, sewers and potentially cables take place through methods including: pipebursting, pipe splitting, pipe eating and lead extraction and lead replacement systems.
PIPEBURSTING: STATIC BURSTING, MANHOLE, HYDRAULIC BURSTER, EXPANDIT PIPE BURSTING, SILT TRENCHES, FRACTURABLE PIPE
Pipe Bursting is a method of online 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. Three methods are commonly used as outlined below.
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. 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
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.
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.
Pipe splitting is similar in technique to pipe bursting 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.
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.
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.
Pipe & cables installation techniques include: impact moling, pipe ramming, auger boring & thrust boring, pipe jacking, micro tunnelling, guided rod pushing, guided boring & directional drilling, rock boring, cable pulling and cable blow in systems
Impact moling is a technique in which a percussive mole (soil displacement hammer) is launched from an excavation to displace the soil and form a bore. The new conduit is normally drawn in behind the mole or pulled back into the bore using the hammers reverse action. Pneumatically driven moles, in which the soil is displaced by the action of a percussive piston, have been developed in the range 30 - 180mm diameter for a single operation, with repetitive multiple passes to achieve 200 - 250mm diameter.
Pipe ramming is a simple technique utilising a pneumatic hammer to drive steel casings through the ground from one pit to another. Rams of pipes up to and over 2m diameter and exceeding 70m in length have been achieved. During the basic operation, the correct size of rammer is chosen by assessing casing diameter, length of ram and the prevailing ground conditions, positioned on the tracing or 'H' Beam in the launch pit, the rammer and first casing length are connected directly or via ram cones, using adjustable cradles or air-bags, the assembly is aligned and levelled on target, the air supply is partly applied to start the rammer and slowly increased as the first casing enters the ground. Full power is applied when the skin friction on the casing is sufficient to overcome the back stroke of the piston, as each casing length is entered the rammer is removed, the next casing welded in place and the rammer replaced and restarted, on completion of the ram, the soil in the casing can be removed by one of several methods including: pressurisation and blow-out, pressure jetting, mini excavator or by any combination.