Category
New installation of pipe/cable/duct for gravity or pressure applications.
Application
Auger Boring can be used for the installation of casing pipe for gas, water, cable , sewer pipeline installations in diameters from about 100 mm (4 in) up to 1,800 mm (70 in) over lengths from a few metres up to 100 m although longer bores up to 200 m have been known. Generally Auger Boring is best applied in soft soils with no or low ground water head, although with special adaptation and equipment rock boring in soft rock can be achieved.
As the system is not sealed ground water head can lead to ground loss through the auger chain.
The systems are non-steerable or have very limited steering capability, so may not be suitable for applications in which line and level accuracy may be required. Auger Boring does also require sufficient space to install the launch pit and boring machine on at least one side of the route being bored.
Benefits
Auger boring is beneficial where road rail or other crossings are required where trenched options would be highly disruptive and inconvenient to the road and rail users, local population and businesses. Auger boring is a non-displacement technique which enables installation without ground heave.
The system is relatively simple to operate with an experienced crew and is relatively non-intrusive to the environment.
Technology Description
Auger Boring is a technique, usually non- or limited steer, for the bored installation of a casing pipe into the ground. Product pipe or final services are then installed within the casing pipe as required. Auger Boring is a Pipe Jacking technique but as the casing pipe is an integral part of the construction methodology it is necessary to understand this concept separately.
The technique is normally found to be cheaper than full Microtunnelling or pipe jacking but does have limitations on the range of ground in which it can operate. In its standard form, in particular very wet ground, it has its limitations as high water tables and flowing ground water can cause ground loss along the auger chain as the excavation assembly is not sealed.
However, with special adaptation it can operate in a variety of ground including rock provided a special rock cutting head is applied to the assembly. Depth limits are dependent on the size of excavation required to allow access for the auger boring unit and the practical length of pipe that can be installed from what is usually quite a large dimension launch shaft/pit.
The excavation technique uses a rotating auger chain/flight fitted with a cutter head. The cutter head is driven by, and is positioned at the lead end of, the auger string that has been established within the casing pipe.
The auger diameter is just less than the full diameter of the casing to allow rotation within the casing. If conditions allow or require for a small over-cut, the cutter head may be positioned just outside the lead edge of the casing pipe but it is still rotated by the auger chain within the pipe. Rotating the helical auger chain within the casing pipe allows the cutter head to excavate the ground at the face, with spoil being removed back along the auger string within the casing pipe to the launch shaft or pit. Spoil is removed by hand or mechanically or placed into muck skips for removal as it exits the casing pipe.
The system is not usually used for installations requiring very high accuracy in line and level, although experienced operators can achieve very good accuracy where ground conditions permit. Systems have been developed that allow for some limited steering capability of the cutter head or to the casing pipe to counter minor deviations as they occur.
The method is best applied in softer ground conditions like clay soils and soils containing cobbles provided they are not of sufficient size to block the auger flight.
Generally, Auger Boring systems are usually diesel or hydraulically driven and are used for non-displacement boring operations. They are designed for the installation of casing pipes from about 102 to 1,830 mm diameter over distances of up to around 200 metres although larger diameter is normally associated with longer bores; typically bore lengths are less than 100 m.
Practical operational capacity depends very much on the machine selected as a number of manufacturers offer differing systems.
The installation process requires the establishment of a launch pit dimensioned to allow the installation and operation of the auger boring machine and the required pipe length to be accommodated within it, or at least the length of pipe that it is practical to work with. As the casing pipe is generally manufactured from steel, the welding together of lengths to create the total pipe length required is not a problem.
The auger boring machine, usually operated by a single operator using controls on the body of the machine, is set up on a set of tracks or rack and pinion system on the line and level required for the casing installation. When the auger boring machine reaches the end of its stroke, governed by the length of the track/rack arrangement, the casing pipe is released and the machine is withdrawn to its original starting point. If required, a new length of pipe is positioned with its own auger flight in place, the auger flights are connected together to drive the cutter head and the pipe ends welded to form a continuous pipe length. The excavation and thrust process is repeated in this way until the drive length required is completed with the arrival of the cutter head at a reception pit.
The drive is completed with the withdrawal of the auger flight chain from within the casing pipe and the casing being cleaned out of all remaining spoil leaving the empty casing pipe in the ground. The product pipe(s), cables or drainage system can then be installed within the casing pipe as required, on a precise line and level if necessary.
Others in this Category:
