New penstock at the Kaunertal hydropower station - site investigation and grouting concept / Neubau Druckschacht KW Kaunertal - Baugrunderkundung und Injektionskonzept

The penstock and the surge tank are being renewed at the two existing hydropower stations of Tiwag (Tiroler Wasserkraft AG) in the Kaunertal valley. The core of the works is the bored pressure shaft about 1,430 m long with an excavation diameter of 5.54 m and armourings of 4.3 m diameter, which is being installed inside a segment lining. When a tunnel is continuously bored by a shield TBM, the system restricts the scope for reaction to changes in rock mass behaviour. Special measures outside normal operation are expensive and time-consuming. In geomechanically difficult sections of the tunnel, the situation has to be assessed continuously to establish whether the expected ground conditions could significantly disrupt the tunnelling system. For this purpose, hammer drilling was undertaken systematically during the advance and seismic investigations were carried out, as well as core drilling.
In order to achieve a secure mechanical connection between the steel lining or the concrete lining and the surrounding rock mass and activate the load-bearing capacity of the rock mass, grouting of the rock mass as well as contact and gap grouting are performed for the steel-lined sections and the concrete-lined surge tank riser shaft. The grouting of the rock mass immediately after the completion of the shaft drive is carried out according to the GIN method with a defined hole pattern and based on extensive tests. The results are systematically evaluated by the start of the contact and gap grouting after the installation of the steel lining.