Both the technical boundary conditions and the usual advance rates achieved during hard rock TBM shield drives severely limit the ability of the on-site-personnel to document the geological conditions and the system behaviour at appropriate intervals. A systematic and continuous short-term investigation of the rock mass conditions is performed on the construction lot KAT2 of the Koralm Tunnel (obtained by impact drillings and geophysical methods). The difference in scales and the fact that no continuous inspection of the ground conditions can be performed lead to a gap between the prognosis and the observed behaviour and a direct comparison is seldom possible. Based on the daily comparison between the observed behaviour and the analysed machine data, a state-of-the-art interpretation method has been developed. This method allows reliable conclusions regarding the primary aspects of the system behaviour and thus enables deductions on the geological/geotechnical conditions which have been encountered. The identification of the relevant parameters and suitable analysis methods has been performed in a "trial and error" manner: machine parameters deemed relevant in theory have been continuously compared with the observations on site and depending on the results, found usable or discarded. Reliable knowledge about the face stability, qualitative degree of fracturing of the rock mass, occurrence of over excavation in the cutter head area, the state of the annular gap and the blockiness of the rock mass can be deduced by applying this method. The results are used on daily basis by the on-site geologist and geotechnical engineer in order to verify the prognosis and recommend additional/auxiliary construction measures.

Backfill of segmental lining -State of the art, redistribution behaviour of pea gravel, possible improvements Tübbingbettung -Stand der Technik, Umlagerungs verhalten von Perlkies, VerbesserungspotenzialWith mechanized shield tunnelling the quality of the backfill is of significant importance for the stability of the lining. The used material affects the interaction between support and rock mass. Therefore, the choice of a proper backfilling material is of great importance for the system behaviour. Scaled model tests have been carried out investigating the relocation behaviour of pea gravel within the annular gap. The tests have shown that especially with Double shielded TBMs a distinct relocation mechanism is triggered by the regripping process. This leads to an unfavourable bedding situation immediately behind the TBM shield. Within a numerical study the influence of an incomplete bedding situation on the section forces within the lining segments has been carried out. The simulations have shown that crack propagation is more likely in unfavourable bedding situations. Nevertheless, numerical simulations have proven that cracks within the segments denote a higher utilization level but do not directly imply an acute danger to the load-bearing capacity. As observed in reality, the state of incomplete bedding represents the relevant load case. A design improvement has been introduced overcoming the temporary state of a partially bedded segmental lining. Furthermore, this approach prevents a large-scale relocation process of pea gravel within the annular gap.

Tunnelling in weak ground under high overburden normally results in very high displacements and if a stiff support concept is applied, this requires a very high load-bearing capacity. This has again and again proved to be both an uneconomical and an unsafe concept, leading to extremely high lining thickness and brittle failure behaviour. In order to avoid such problems, ductile support systems have been developed, which allow controlled deformation of the ground and plastic dissipation of excessive stresses accumulated in the lining. For the efficient design of such systems, the aspects of spatial and time-dependent development of displacement, time-dependent properties of shotcrete, and the load-displacement behaviour of the ductile elements have to be harmonized.The requirements posed on a ductile support system are presented, together with simple principles for the determination of ground behaviour boundaries when the application of a ductile support becomes imperative. Recent developments of ductile elements for use with shotcrete linings are described, and their general performance and efficiency are reviewed. A method for calculation of shotcrete stresses using absolute displacement monitoring data is presented, allowing the identification of both inefficient (lining stresses too low and strongly variable in the cross-section) or unsafe (lining stresses almost exceeding the strength) concepts and optimisation during construction.

It is state of the art to drive long tunnels in Alpine areas using hard rock TBMs. Mechanised tunnelling has much less flexibility than conventional excavation, so a deeper analysis of the available geological and geotechnical fundamentals is needed. In the course of planning the mechanised drives of the main tunnels on the Austrian side of the Brenner Base Tunnel, a detailed tunnelling concept was created, which deals with the project‐specific features and boundary conditions. The exploratory tunnel, which is used for geological and geotechnical exploration for the construction of the main tunnels, is currently being excavated. Through additional analyses, the geotechnical model could be verified and a reliable update of the rock parameters and the associated critical decisions has been achieved. All further specifications regarding TBM requirements, additional and auxiliary measures, support concept, bill of quantities and construction time model were based on the prognosis of system behaviour.

The paper deals with the challenge on structural analysis, logistics as well as on geotechnical aspects during sinking of an approximately 60 m deep construction shaft with a cross-sectional area of about 720 m 2 at the Koralm Tunnel lot KAT 2. Numerical 3D simulations were used for the structural analysis. The results in terms of level of loading of the support measures and the displacements served as a basis for predicting the system behaviour of the shaft. During sinking, the behaviour of the shaft and surface was continuously monitored within the geotechnical safety management by means of 3D displacement measurements, measurement of strains in the shotcrete lining and measurements of pile inclinometers. Thereby a continuous target-performance comparison was accomplished. Special characteristics in the design and construction phase are illustrated and discussed.