Installation of New Pipelines
The term micro-tunnelling applies to remotely controlled, steerable, controlled evacuation tunnelling methods for pipelines of 1000mm diameter or less and usually for lengths up to 200 metres. The spoil is removed from the cutting head within the new pipeline which is advanced by pipe jacking.
Micro-tunnelling systems have been developed to work from drive shafts in most ground conditions. Spoil may be removed by auger, slurry conversion or vacuum extraction.
Micro-tunnelling machines are controlled from the surface, with location and operation of the machine being continuously monitored, usually by means of a laser guidance system.
The high accuracy required when installing gravity sewers, combined with work where minimum disruption is required, makes micro-tunnelling ideal for such work. The technology has developed where machines are now readily available to drive 100 metres or more for sizes from 100mm diameter upwards from drive shafts down to 1.5m in diameter. Accuracy, even below the water table, is typically + or – 20mm over these distances.
Pipes for pipejacking are produced in most conventional materials with special joints, and in special short lengths, to accomodate the needs of micro-tunnelling. Steel, Hobas, Clay and Concrete Pipes have been designed with the high forces of jacking in mind.
Short Drive Systems
A number of short drive, inexpensive, unguided tunnelling systems with low mobilisation costs are in common usage. They are used for short house connections or for short crossings of obstacles. These systems include:
- Auger Boring
- Impact Moling
- Rod Pushing
- Pipe Ramming
- Thrust Boring
Horizontal Directional Drilling
Originally developed by the oil industry in the United States, this technique is now widely used for all pressure pipes under major obstacles such as motorways, large rivers, airport runways etc. A steerable drill bit of 90mm diameter is launched from the surface at 10′ -15′ and produces a pilot hole. This is followed by a 125mm washover pipe. Upon completion, the pilot string is removed and a rotating barrel reamer travels back along the washover pipe. Subsequent reaming continues until the required diameter is achieved. Drives of more than 1000 metres and up to 1 metre in diameter have been carried out.
A smaller, less expensive version of directional drilling for installing pipelines in the 30mm to 300mm diameter range for drives up to 150m. Guided Boring uses a small diameter, steerable drilling head for excavation which is thrust from the surface and launched at an inclined angle. Monitoring is achieved by using a transmitter in the head and a location device at ground level.
Rotary moling is a stecrable boring system using a slanted face at the head of a flexible drill string. This acts as a pilot bore for a reamer which then pulls the product pipe through.