Mechanized Shaft Construction for Utility Tunnelling.

Where sinkings are made by vertical shaft sinking machines, great demands are placed on the lining of the shaft in terms of precision, efficiency and safety. Dependent on the requirements of the project, the shaft can be lined with precast concrete segments, in situ concrete, steel segments or, provided the soil is free from groundwater, also with rock anchors, steel mats and shotcrete.

The shaft is lined with concrete segments or in situ concrete at the surface of the shaft parallel to the tunnelling being carried out by the excavating machine. The segments are joined together to form a ring segment by the crane fitted to the shaft sinking unit and are positioned on the respective lead ring segment and sunk in a controlled manner into the undersoil by cylinders. This enables the pressure tight lining at the end of the shaft to be completed at the same time as the shaft is sunk. The tightness of the lined shaft, the quality of the segments and the time spent on the modular construction are the main factors to be taken into account in the construction of the required shaft lining.

To reduce the frictional forces arising during sinking, the annulus is lubricated by a bentonite lubricating system in accordance with the pipe jacking in the microtunnelling. In the case of steel segment linings, steel segments are used which, after a bored depth of about 0.7 to 1.0 m has been reached, are let down into the shaft, where they are fitted to a ring under the protection of the steel can, lifted up hydraulically, screwed to the last steel ring and anchored to the rock by special fixing devices. Mortar is injected under pressure into the gap formed by the intersection of the rock and the steel segments.

Where shotcrete is used to line the shaft, either rock anchors or steel mats, dependent on the geological conditions, are used to stabilize the surrounding soil. The range of application of this process extends from stable soils up to medium solid rock: with mixed or loose soils the soil would break in at the sides.

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