Laying of communications with a trenchless method, microtunneling
Trenchless technologies allow performing underground construction without ground opening. Applying of trenchless technologies allows performing 90% of work underground, that excludes:
- the necessity of reinstating the surface of motorway
- disturbance of town-living practiced rhythm
- traffic arteries closing
- damaging of existing
Trenchless technologies are economically competitive (2.5-3 times) with traditional method, moreover laying of communications with a trenchless method doesn't damage the environment.
The recent tendency shows that public utilities of megapolises in different countries draw more and more attention to the issues concerning using of trenchless technologies for reconstruction and laying of water-line, drainage and other utility network; trenchless technologies are an alternative to traditional trench method of construction and reconstruction of pipes.
The problem of reconstruction and pipeline laying can be solved with wide use of trenchless technologies and special equipment. Currently the most promising equipment for these works is microshields, horizontal drilling rigs and pneumatic drifts.
Each piece of equipment has its efficient sphere of application in terms of diameter, depth, distance, hole making accuracy, type of ground, communication appropriation, working conditions on the jobsite and many other factors.
For shallow run (up to 5 metres) short (up to 50 m) engineering communication laying through traffic and rail roads it is efficient to use pneumatic drifts.
The laying of communications through water barriers in given direction is performed by means of horizontally-directed drilling rigs. For this method special drilling rigs performing rough (pilot) drilling along precomputed pathway with further bore enlargement and pipe laying are applied.
Underground communications up to 80 m deep and up to 1.5 km long with departure of 30 mm from project are laid in the cities by means of microshields. In this case two trenches, starting and receiving, are used; their depth matches the laying depth. Powerful adjustable jack station where tunneling shield is placed is set in the starting trench. Moving of the shield in the ground is provided by means of adjustable jack. The assembling of pipes is performed with building up of pipe column, i.e. the heading to the receiving trench is carried out. The accuracy of heading is provided with computer operation complex with laser system positioning of shield.
Microtunneling technology allows laying pipelines in various ground - from unstable sand clay and water sand to the rock ground. The cutting attachment of header is chosen according to the type of ground that allows reaching optimal parameters of heading.
- Microtunnel boring machines of all cut diameter with ground hydrotransport for laying of communications of various types;
- Microtunnel boring machines with screw transportation of ground;
- Microtunnel boring machines with pneumatic transportation of ground;
- Puncture-drilling rigs (the ground is not excavated from the bore, but is pushed apart in radial direction with formation of consolidated zone around the bore)
- Puncture rigs (the puncture is performed with small steel-channel-line-shaped dolly in the bore for cable laying with diameter up to 100 mm)
Pipes used for microtunneling
Polymer-concrete, reinforced concrete, ceramic, glass reinforced plastic and asbestos-cement pipes of all diameters are used for trenchless laying of the communications with microtunneling. For linkage of pipes special pump buckets are used in order to eliminate water entry through connection joints.
Trenchless technologies are used for the following works:
- Laying of communication cables;
- Oil-gas-heat pipelines laying;
- Laying of canalization and water pipes;
- Pile and pile structures formation; consolidation of crowns of underground construction;
- Pipe replacement, destruction of old pipes with laying of the new ones.