Development of large diameter multi-pipe bundles for long distance no-dig installations

Abstract

The design options and practical solutions for installing large diameter multiple pipe ducts over very long distances have been explored. The work has involved consideration of the groundwork problems of microtunnelling or directional drilling at up to 1·5 m (60 in) diameter and 7 km (4·5 mile) distance and installing a multi-utility pipe formed by continuous jointing of pre-assembled multiple pipe bundles. The practicalities of pipe assembly and fusion welding have been addressed and a design solution demonstrated for arrangements of up to seven 110 mm (4·5 in), polyethylene (PE) pipes within a 400 mm (16 in) PE pipe containment duct. Applicable on a much larger scale, this solution envisages factory assembly of the subducting within the outer pipe with precision alignment of pipe ends so as to permit continuous butt fusion of lengths on a moving base as the system is drawn into a tunnel. The work on PE pipe systems has involved developing a means of assembling and locking together the subduct components as a bundle of individual pipes. This is achieved by using a series of locking rings spaced to form a rigid structure. The envisaged requirement for butt fusion welding long lengths, on a continuous basis, demands simplification of the welding procedure for a pipe array. The present work has shown that it can be achieved by a near conventional butt fusion operation, using a single large diameter hotplate. Successful jointing is however only feasible if the multiple pipe bundles can be maintained in precise alignment during simultaneous welding. To make this practically possible in field conditions, each pipe bundle is factory fused to a precisely moulded end assembly, carrying alignment keyways. To date only one pipe bundle geometry has been fabricated, at an outside diameter of 400 mm (16 in), but it is believed that the technique will be applicable at much larger diameters and with varying diameters and types of subduct. The research activities to further investigate the feasibility of high voltage cable pipes are continuing within a joint academic project at Birmingham and Newcastle Universities. This is believed to be a currently unique approach to the provision of high voltage cable ducting and multi-utility pipework by exploiting trenchless (no-dig) technologies. It is particularly applicable to civil engineering projects involving long distance tunnelling under extended stretches of water such as harbours and offshore installations or in difficult terrain such as hillsides. The technology is appropriate to conducting power from new energy sources such as wind farms, tidal power plants, small scale hydroelectric systems, or solar power units and linking such resources to major power grids without the need for overhead pylons.