12-12-2012, 03:56 PM
TRENCHLESS TECHNOLOGY
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ABSTRACT
Trench less technology is the science of installing, repairing and renewing underground Pipes, ducts and cables using techniques which minimize or eliminate the need for excavation. It can reduce environmental damage, Social costs and produce in alternative to open trench method of installation, renewal and repair it includes in, development of all kinds of underground napping techniques, tunneling devices and specialist materials and equipment.
Trench less technology is basically making a tunnel below the surface and staling service lines like water or gas pipes, electric or telecommunication cables etc. without any disturbance to the public. It also makes it possible to install the utilities under rivers canals and other obstacles with no disruption of flow and with minimum or no damage to the environment.
INTRODUCTION:
Demand for installation of new underground utility systems in congested areas with existing utility lines has increased the necessity for innovative and economical systems to go underneath and alongside in-place facilities. Environmental concerns, social (indirect) costs, new and more stringent safety regulations, difficult underground conditions (containing natural or artificial obstructions, high water table, etc.) and new developments in equipment have increased demand for trenchless technology. Trenchless technology methods include all methods of installing or renewing underground utility systems with minimum disruption of the surface or subsurface.
Trenchless technology has become popular for underground utility construction road crossings. In recent years, there has been remarkable progress in development of new trenchless technology equipment and methods. These developments have produced improvement in jacking force capacity and increased drive length, improvements in steering and tracking systems, availability of new and different types of pipe and other advancements. Preparation of design guidelines, construction specifications, process inspection, materials testing, and the training of engineers, construction and permit inspectors in contracts and bid documents, has not kept pace with new developments. Most all governmental agencies, with a few notable exceptions, are not current with capabilities and limitations of the new methods, materials, and equipment.
Developed from the directional and deep drilling technologies, HDD is the ideal steerable drilling method for the trenchless installation of pipes and cables. Utility and communication providers swear by the benefits of HDD technology because of its capability to provide them with numerous customized solutions for virtually any problem. Because of its many applications, it is necessary to systematically capture and outline the full range of the HDD technology, so that it can be effectively communicated to the engineers and decision makers of today and tomorrow.
METHODS OF TRENCHLESS TECHNOLOGY
Trenchless technology methods systems have been categorized in to two groups:
1. New installation
2. Rehabilitation and Renovation
1. NEW INSTALLATION
Methods for installation of a new pipeline or duct, including dealing with service connection are:
A) Micro tunneling.
B) Horizontal directional drilling.
C) Guided drilling.
A) MICRO TUNNELING .
Micro tunneling is a term which is used to describe remotely controlled mechanical tunneling systems where the spoil is removed from the cutting head with in the new pipe line which is advanced by pipe jacking.
Micro tunneling machines have now been developed to work from drives shafts in almost all types of ground conditions. The cutting head has to be carefully selected to deal with the expected ground conditions, with the appropriate cutting tools and crushing devices for the range of gravels, sands, slits, and clays.
The only excavating required from the service is for drive and receptions shafts. Spoil may be removed from the face by an auger running through the newly installed pipeline to a skip in the base of the drive shaft.
Alternatively, water may be used to convert the soil into slurry at the cutting face. The slurry is less then pumped to the surface where the solids are separated before disposal.
B) HORIZONTAL DIRECTIONAL DRILLING .
Horizontal drilling systems are nowadays widely used for installing pressure pipes under major obstacles such a motor way intersections, large rivers and airports runways.
A small rotating and steerable drill bit is launched from the surface at an angle 10-15 and is used to drill 90mm mud filled diameter hole. During the drilling operation a 125mm diameter wash over pipe is drilled over the pilot string and following some 100mm behind the head. Alternate drilling then continues on the pilot string is removed and the bore is enlarged by a rotating barrel reamer attached to and pulled back by the wash over pipe, drilling mud being used to lashed away the cuttings and to support the reamed hole. Subsequent caming continues until required diameter is achieved. The product pipe is less than attached to the reaming head and pulled through the bore drives of more than 1.5km and of up to 1200mm diameter have been carried out.
C) GUIDED DRILLING
Guide drilling employs an excavation or soil displacement with compact lightweight rig for rapid mobilization. Small diameter jets mechanized cutting tools or displacement heads attached to a flexible drill string are positioned to form a bore as the head is thrust forward. The drilling head is launched from the surface at an inclined angle. Controlling the orientation of a slant face at the head effects steering in both vertical and horizontal planes. Monitoring of the alignment takes place using a transmitter in the head and a locating device at ground level.
2. REHABILITATION AND RENOVATION
Methods included are:
A) Pipe bursting.
B) Pipe eating.
A) PIPE BURSTING:
In this method an existing pipeline can be replaced with a pipeline of the same or larger dimension without opening up the ground. It is especially useful in areas where the load on the system is more than the existing pipe can handle and replacement is required.
The method uses a mole as a bursting head that is drawn through the existing pipe crushing it as it moves forward and replacing it with a new PE (polyethylene) pipe. The main advantage of this system is that a small power source can be used to drive the mole with minimum time. Upsizing from 100mm diameter to 225mm diameter is now well established, and pipes of up to 600mm diameter have been replaced.