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The application of bearing yet yielding shotcrete shells is based on the engineering principle: In squeezing rock, the rock pressure decreases with increasing rock deformation.
An implementation of this principle are tunnel linings made of shotcrete shells with integrated deformable hiDCon® - elements. The result is a bearing yet yielding lining that reduces rock pressure.
The shape and number of hiDCon® elements per cross section depends on the amount of permitted radial deformation. The hiDCon® elements resist the shotcrete lining with a predetermined bearing capacity so the shotcrete does not become overstressed. The hiDCon® elements are designed so that after exhausting their working range only small additional deformations develop. The lining resists these (small) deformations with the full bearing capacity of the shotcrete shells.
Picture 1 shows the shotcrete lining with integrated beam shaped hiDCon® elements in the Lötschberg Base Tunnel, Switzerland. Picture 2 shows hiDCon® elements being fitted between two steel arches. The steel arches have sliding connections between their segments to allow for convergence. The deformation capacity of the hiDCon® elements stops the shotcrete shell from becoming overstressed, even at large convergences (Picture 3).
In the Lötschberg Base Tunnel, Switzerland, 180 meters of the section that passed through a heavily squeezing rock zone under high overburden conditions was lined with hiDCon® elements.
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Finished Projects / Lötschberg Base Tunnel : Yieldable 
