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As a result of several feasibility studies from which sound economic and technical arguments emerged, the decision was made to construct a new headrace system for the Rodundwerk I consisting of a low pressure tunnel, a shallow pressure shaft parallel to the surface slope and a subsequent high‐pressure penstock gallery. The new distribution pipeline was designed as a concrete‐encased gravity abutment. Construction started at the beginning of May 2020 and since then excavation work has progressed according to plan. Particular attention had to be addressed to the impact of construction operations on the existing power plant structures. Hence, a detailed monitoring concept was established concerning the vibration transmission in the rock mass. Excavation works are carried out partly by tunnel boring machine, partly by drilling and blasting and, once the critical threshold of vibration has been reached, by alternative methods. By continuously adjusting the blasting parameters (charge amount, ignition timing), it was possible to minimise the detonation‐related effects in the vicinity of the existing structures. [ABSTRACT FROM AUTHOR]

The article reports that between June 2014 and autumn 2017, the Rellswerk, a small power station by illwerke vkw, was built and put into operation. Topics include considered that the Rellswerk is located in the Rellstal, a side valley of the Montafon in southern Vorarlberg/Austria and with the pump turbine water that is drawn in via the two streams Vilifau and Zaluanda is pumped into the Lünersee, which is around 550 m higher.

The proposed method can be seen as an adaption of the "Seeber" concept considering developments in geomechanics, calculation methods and steel technology over the last decades. When exposed to inner pressure, the cracking condition is transgressed and steel linings will not protect the rock mass against cracking. Accordingly, the post‐failure behaviour of the rock mass is an essential basis for structural design. The effects of crack water pressure on radial displacements and the width of gaps are considered. The resistant behaviour of the rock mass is determined by its minor primary principal stress. Under mountain ridges and slopes, there is no correlation between the minor stresses and the height of overburden. Obviously damage cases in concrete lined tunnels are the result of inappropriate assessment of principal stresses. A better approach is proposed based on fundamental considerations and FE calculations. Crack water pressure close to the level of the minimal principal stress will induce progressive hydraulic fracturing in the rock mass, which requires safe waterproofing sealing of the shaft. Grouting the coaxial gap in rock mass is a firm part of any design concept. In shafts sealed by membranes, the capability to bridge fissures must be proved by tests. In steel lined shafts, the usable passive resistance of rock mass is determined by the acceptable radial displacement. [ABSTRACT FROM AUTHOR]