Page 1 Page 2 Page 3 Page 4 Page 5 Page 6 Page 7 Page 8 Page 9 Page 10 Page 11 Page 12 Page 13 Page 14 Page 15 Page 16 Page 17 Page 18 Page 19 Page 20 Page 21 Page 22 Page 23 Page 24Specially rebated leading pipes can be produced for insertion into the jacking shield. Similarly, special rebated pipes are produced for the trailing pipes at intermediate jacking stations (interjacks). Leading pipes at interjack stations can be supplied to fit directly to an interjack shield or may be produced with an integral interjack shield. Packers must be incorporated into each joint in order to distribute the jacking pressure and avoid point loads to prevent damage to the ends of the pipes during the jacking process. Medium density fibreboard (MDF) has been found to be the best material from which to fabricate joint packers. Research carried out by the Pipe Jacking Association has shown that MDF is the most suitable under repeated loading of the timber based materials, having excellent recovery characteristics. The packers should not extend over the full joint width, a small gap being left to the inside surface of the pipes to prevent localised spalling. In the UK concrete jacking pipes are manufactured to comply with the requirements of BS EN 1916 and BS 5911-1. Products should be manufactured under a third party certified quality management system complying with ISO 9001 and the pipes should be kitemarked. Concrete pipes are designed to meet the load class defined in the product standard, although higher strength classes can be manufactured where circumstances demand. The pipes and joints are designed to withstand jacking loads applied during installation, and information on jacking strengths should be obtained from the manufacturer. Pipes are normally supplied in lengths of between 1.2 and 2.5 m and feature a joint incorporating an elastomeric gasket to provide a watertight connection. The joint design includes including capacity for joint deflection and draw as defined in the product standard. Secondary seals may be incorporated into the joint if required. Concrete pressure pipes can also be supplied. 20 An introduction to pipe jacking and microtunnelling 5 PIPE JACKING PIPES CONCRETE PIPES 5 Pipe jacking pipes Typical flexible joints Rebated lead pipes Interjack pipes A range of materials are used as pipe jacking linings including concrete, grp, clay and steel. The selection of linings is generally dependent on the application and in some cases ground conditions. Where inherent strength and accuracy is required, for example in gravity drainage in urban locations, factory made concrete, or vitrified clay in the smaller diameters, is usually preferred. Grp pipes, specialist internal linings and high pressure joints are available to meet specific site or project requirements. Steel pipes are also used, either as a primary lining, where appropriate, or as a sleeve for the installation of a range of utilities, gas, water and electricity or other cabling applications. Standard diameters for concrete pipes are in the range 450mm to 2400mm although larger diameters can be manufactured to meet specific requirement. Planning for safe handling and storage of pipes should be part of the scheme design. Clay pipes are commonly available in the range 150mm to 700m. Steel pipes can be manufactured to meet project requirements. Advice on jointing techniques, site handling, and joint packings should be obtained from the manufacturer.