Displacement methods of trenchless pipeline construction comprise a diversity of systems offered as potentially cost effective against
conventional open cut methods.
The paper attempts to look at some of the factors that influence this cost
effectiveness including the choice and suitability of system, knowledge about the operational environment, and the consequences of surface and subsurface 'disturbance'.
In the case of disturbance the discussion concentrates on on-line replacement since as a simple consequence of the pipe sizes involved this is typically the worst offender.
As far as possible the material relates to British Gas experience particularly with on-line replacement and off-line (guided and unguided) pipelaying systems. The information on methods is supplemented by a section dealing with development work at the British Gas Engineering Research Station on guided pipelaying systems.
Finally the paper takes a brief look at what the future might hold for displacement based trenchless techniques and the factors that will influence and contribute to any change in their market share.