2. Maintenance & Repair

3. Renovation

4. Replacement & New Installation

Replacement
The replacement of a pipeline involves the construction of a new pipeline in the same
or a new location to incorporate the function of the existing pipeline. This can be
achieved by:
1) Directional drilling, pushing or boring
2) In situ replacement/Pipebursting

4.1 Directional Drilling, Pushing or Boring

Many techniques are available for the installation of new pipeline or cable; they
They differ in their uses and capabilities. They can be classified as:

1) Horizontal boring

2) Small diameter directional drilling

3) Large diameter directional drilling

4) Microtunnelling

5) Pipe jacking

6) Conventional tunnelling

4.1.1 Horizontal boring

Horizontal boring includes methods in which miniature tunnels are excavated by
mechanical means. These are non man-entry systems. The methods are:

1) Auger method

2) Slurry method

These are considered to be non-steerable methods. The vertical alignment can be changed during the boring process, but the horizontal alignment is not adjustable and depends on the initial alignment, as well as the ground conditions. These methods often require the excavation of pits down at the level of the proposed installation. These are referred to as an entrance pit and an exit pit.

4.1.1.1 Auger method

This is the process of jacking a casing from an entrance pit while simultaneously
removing the spoil with a continuous flight of augers. The auger is driven by a power
source in the entrance pit which transmits power to the cutting head. As the auger
proceeds, pieces are added until it exits into the exiting pit. The auger is then removed
and the pipeline or cable is put into place. Typical diameters range from 100 to 2100 mm, with driving lengths up to 180m.

4.1.1.2 Slurry method

This method differs from the auger method in that it uses drill bits and drill tubing
instead of cutting heads and augers. A slurry mixture is used to keep the drill bit clean
and assist in the spoil removal. The fluid is not used to cut the face of the tunnel;
cutting is done mechanically. The pipeline or cable is then placed upon removal of the
drill tubing (see Figure 18 for details).

4.1.2 Small diameter directional drilling

A typical steerable method consists of a boring head and a spoil removal system. The
head contains a transmitter which enables the user to know the location, depth, and
attitude of the steering head. This information is used to steer the head by a variety of
techniques.

1) Displacement/compaction (rod pushing)
2) Hydro-jet drilling
3) Pneumatic, rotary air drilling


Typical diameters for small diameter directional drills range from 45 to 200 mm, with
driving distances up to 180 m. A typical drilling machine is shown in Figure 19.

4.1.2.1 Displacement/compaction (rod pushing)

These systems literally push a rod through compactible to displaceable soils. The
steering head is tapered on one face. To maintain a straight path, the rods are rotated as they are pushed forward. However, if the rods are pushed without rotation, the head will pull the rods in the direction of the alignment of the taper. Location, depth and
rotational attitude are relayed to the driller by means of two-way radio contact with the
operator.


As with other directional boring systems, once the bore has reached its target, the
steering head is replaced with a reamer and the new cable or pipe, and the total assembly is pulled back to the entrance pit.

4.1.2.2 Hydro-jet drilling

These systems drill the holes, through which the utilities will be pulled, by using a
mixture of water and drilling mud, usually bentonite. The jetting nozzles are aligned on
one side of the steering head only. When the drill rods are rotated and pushed ahead, they will travel in a straight line. When the rods are pushed without rotation, the jetting
action will form a void on one side of the steering head, causing the bore to steer in
that direction. This operation is controlled by the driller, who is in two-way contact
with his co-worker standing on the ground surface over the remote end of the bore,
monitoring the signals transmitted from the steering head.


Once the steering head has emerged from the connecting pit, a reamer is attached
between the drill rods and the utility pipeline or cable to be installed. The complete
assembly is then pulled back, maintaining rotation, through the mud-lined hole created by the hydro-jet drilling operation.

4.1.2.3 Pneumatic, rotary air drilling

Both of these systems operate similarly to other directional boring techniques except
that the steering head consists of either a pneumatic piercing tool or a steerable air
rotary drill head. These systems can be used in hard ground or rock.


The pneumatic piercing tool has a tapered steering attachment similar in appearance to the steering head used for the rod pushing. The operation and control of these two systems are almost identical.


The air rotary drill head was originally developed to meet the requirements of the oil
well drilling industry. As with the other systems, the head contains a transmitter to
relay its position and depth, etc. However, the steering mechanism is completely
different. Straight advance is maintained by rotating the full drill head and drill stem.
Steering is achieved by rotating the patented cutting tool independently, with the drill
stem being pushed forward without being rotated.

4.1.3 Large diameter directional drilling
Large diameter directional drills can be used for distances up to 2000 m, depending on the ground conditions, with typical diameters range from 200 to 1200 mm.


These large systems operate similarly to the smaller scale methods, but require
considerably more working area at both ends of the crossing or drive, and rely on very
sophisticated downhole instrumentation to continuously monitor the position and
orientation of the steering head. The guidance technology was originally developed for
directional oil well drilling. The information transmitted from the head is displayed on a
console in the drillers' control cabin. Adjustments to maintain line and grade can be made automatically but most companies still use manual controls.

Both hydro-jet and air rotary drilling techniques have been successfully used in
various ground conditions. As with the smaller systems, steering is achieved when the
drill rods and head are pushed ahead without rotation. The rock drill head has a separate downhole motor for rotating the bit in the desired direction while the non-rotating part of the head and the drill stem are pushed. Other systems rely on a bent section of drill bar for steering. Straight travel is produced by rotating the complete head and drill stem assembly.

Due to the larger diameter hole required, the initial pilot has to be reamed two or
three times before it is large enough to accept the pipeline. The radius of curvature or
sag is determined by the size and type of pipe to be installed.

These types of systems are particularly advantageous for river crossings, since the
pipe or cable can be buried at considerable depth, ensuring protection from ships and
future dredging of the river bed (see Figure 20). From the environmental standpoint, this installation method does not disturb the river ecology and eliminates the need for open excavation and cofferdams in the river. Depending on the ground conditions and a good operator, a very accurate bore can be drilled to any preset profile.

4.1.4 Microtunnelling

Microtunnelling is a horizontal boring technique which utilizes highly sophisticated,
laser-guided, remote-controlled equipment. This enables the user to monitor its precise
location and to ensure accurate line and grade. This system typically consists of a
steerable tunnelling machine which is jacked from a shaft ahead of the permanent pipes or a temporary casing. The spoil is removed by using either the auger method or the slurry method.

The auger method uses a continuous flight of augers to remove the spoil (see Figure
21). The auger is surrounded by a casing placed inside the permanent pipes or the
temporary casing. The slurry method uses a slurry mixture to pump the spoil back to the
surface, as seen in Figure 22.


Typical diameters range between 150 and 1200 mm, with driving lengths around
180

4.1.5 Pipe jacking

Pipe jacking is a trenchless technology which is used for man-entry systems. The area around the end of the pipe is excavated, either manually or mechanically. This is done by shovel and pick or by using an auger. The spoil is removed by a flight of augers, carts, or conveyors. As the area at the head of the tunnel is excavated, the pipe is jackedforward from a jacking pit. The rate at which the pipe is jacked forward depends upon the soil conditions. After the pipe is jacked forward, the hydraulics jacks are extracted and a new piece is added. Because of the forces exerted on the pipe during the jackingprocess, the design and layout of the jacking pit is critical. The type of pipe used must be able to withstand the enormous forces during the jacking process.


Because this is a man-entry system, the diameter is usually greater than 900 mm.

4.1.6 Conventional tunnelling

Conventional tunnelling is similar to pipe jacking; it is used for man-entry systems.
The tunnel is excavated manually or mechanically, and the spoil is removed using an auger system, carts, or conveyor. The difference is in how the pipe is installed. The pipe or tunnel liner is added to the face of the tunnel, as opposed to the other end. A temporary casing precedes the liner plates, which are assembled at the face of the tunnel and added on. The temporary casing is then jacked forward against the liner, as opposed to the entire length being jacked forward. Additional pieces are added and the procedure continues. The diameters are usually greater then 1.2 m, with no upper limit. The driving distance is also unlimited.

4.2 In Situ Replacement

This is the replacement of old or damaged sewer or utility lines with a new pipe along
the original alignment. This can be done using two techniques:

1) Pipe bursting

2) Microtunnelling

4.2.1 Pipe bursting

The deteriorated existing pipe is expanded outwards by means of an expansion tool (see Figure 23) and the new pipe is either towed behind the tool or jacked into place using conventional pipe jacking techniques. Renewal by pipe bursting necessitates the
reconnection of laterals by excavation from the surface.


When a pneumatic piercing tool or hydraulic bursting mole is used to break and expand
the existing pipe, the tool is generally winched from manhole to manhole with a new
polyethylene pipe towed behind it. Other types of replacement pipe can be used, but they must be installed immediately behind the expansion operation by means of pipe jacking.


Another style of expanding hydraulic pipe breaker is advanced by the new pipes as they are jacked in behind it. The demolition process is monitored by an in-pipe CCTV and visually displayed on the operator's video monitor above ground.


Where ground conditions permit, the expansion of the existing pipe can be increased to
permit the installation of a larger diameter service pipe. Typical diameters range from
100 to 600 mm, with driving distances up to 100 m.

4.2.2 Replacement using microtunnelling

The existing pipes are literally mined by a suitable crusher-type microtunnelling
machine (see Figure 24) and the new pipes installed as described elsewhere in this report under Microtunnelling. Alignment is maintained by a probe and packer attached to the front of the tunnelling machine.

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