ABSTRACT: Grouting is a key element in hydropower construction, as it enhances the long-term stability of a conduit. Grouting for pressure tunnels and shafts can be grouped into rock mass and structural grouting operations. Structural grouting refers to either contact grouting focused on a structural enhancement of the cast concrete lining or to more complex pre-stressing operations, focusing on coupling of the lining and rock mass. An economical structural grouting system relies on a continuous realization, with standardized work sequences and cycles, which depends on rock mass features and the characteristic of structural interface. Typical grouting criteria are not applicable for structural grouting works, which potentially leading to severe technical, economical, operational and contractual implications during execution. The characteristic features of the interface in between the lining and rock mass must be outlined within tender specification for a fair tender process and an economical operation. 1 INTRODUCTION Grouting is a key element in hydropower construction with the intention to sustainably restore the bedding conditions of the lining and to preserve rock mass conditions in the close vicinity of the conduit over the lifetime of the structure. From a technical point of view, the grouting works can be separated into rock mass and structural grouting operations. Rock mass grouting seals and strengthens fractured rock masses. Structural grouting is intended to assure the bearing capacity of the lining during operation and maintenance. Structural grouting covers inter alia contact grouting and passive pre-stressing of a concrete lining. In addition, skin grouting and filling operations belong to the group of structural grouting operations. Contact grouting refers to any filling at low pressure (< 5 bars) of unintentionally created voids resulting from shaft and tunnel excavation and/or lining methods (AUA 2003). The intention of the contact grouting is to preserve the long- term bedding conditions of the lining. Opposed to the passive pre-stressing operations, which focuses in addition on a long-term coupling of the lining and the substrate. Durable grout is injected into a gap, which has formed as result of the shrinkage processes. In addition, pre-stressing of a concrete lining by high pressure grouting allows for the compensation of thermal losses during the filling operation and creeping processes (Lauffer 1989 and Krenn et. al 2013). The stiffness of the rock mass and concrete, Operational analyses of pressure tunnel and shaft grouting operations Helmut Wannenmacher Gaia Ground Engineering, Widnau, Switzerland Andreas Heizmann Marti Geotechnik GmbH, St. Leon-Rot, Germany Sewerin Sabew Marti Geotechnik GmbH, St. Leon-Rot, Germany EUROCK 2015 & 64 th Geomechanics Colloquium. Schubert & Kluckner (ed.) © ÖGG