State-of-the-art report: progress in the eighties
The optimal modes of concrete mix pressing realized in German and Japanese concepts are different. The German concept of the so–called ‘extruded lining’, developed by Hochtief AG Company, is based on the principle of sustaining the fresh concrete mix under substantially constant pressure throughout the process of shield tunneling. The Japanese concept is being developed by a number of companies and has been introduced in more than ten different schemes. The ring by ring pattern of lining concreting and pressure moulding makes it possible to use rod reinforcement. Moreover, a variety of composite lining structure has been proposed, e.g. those combining steel with concrete, precast and in–situ parts, as well as prestressed lining solution, all of them conductive to improved structural strength at the cost of somewhat sophisticated underground construction procedure.