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  Seismic prediction and imaging of geologicalstructures ahead of a tunnel using surface waves Zur Erlangung des akademischen Grades eines DOKTORS DER NATURWISSENSCHAFTEN von der Fakult¨at Physik desKarlsruher Instituts f¨ur Technologie (KIT) genehmigte DISSERTATION von Dipl.-Geophys. Stefan Jetschnyaus Dresden Tag der m¨undlichen Pr¨ufung: 30.April 2010Referent: Prof. Dr. Thomas BohlenKorreferent: Prof. Dr. Wolfgang Rabbel1  ”...time takes too much time...”R´ os´ın Marie Murphy (1973 -)  f¨urJ¨org “diddie” Dietrich “Gruß und Frieden”  Abstract To increase safety and efficiency of tunnel constructions, online seismic exploration ahead of a tunnel can become a valuable tool. By correlating predicted geological structures, such asweak or water bearing zones and lithological interfaces, with the known geological situation,the tunneling process can be optimized. Time consuming and thus expensive downtime can beavoided and the construction site as well as the surface is less exposed to safety threads. Thisis especially important for the tunneling in urban areas, which mainly involves the utilizationof tunnel construction machines (TBMs) below the water table.We developed a new forward looking seismic imaging technique that implies less interferencewith the mechanical tunneling. Our approach is based on the excitation and registrationof tunnel surface waves (TS-waves). These waves are excited at the tunnel wall behind thecutter head of a TBM and travel into drilling direction. When arriving at the front face,they generate body waves (mainly S-waves) propagating further ahead. Reflected S-waves areback-converted into tunnel surface waves (”TSST”-waves) and can be recorded by geophonesmounted on the tunnel wall. Using 3-D Finite Difference modeling, an analytical solutionof the wave equation in cylindrical coordinates and field data acquired at tunneling sites,we investigated the propagation characteristics of tunnel surface waves in terms of dispersionand polarization. It could be shown that at higher frequencies, i.e., if the tunnel-diameter issignificantly larger than the wavelength of surface waves, these surface waves can be regarded asRayleigh-waves confined to the tunnel wall and following helical paths along the tunnel surface.For lower frequencies, i.e., when the tunnel surface wavelength approaches the tunnel diameter,the propagation characteristics of these surface waves are similar to S-waves. Understandingthe excitation and propagation of TS-waves is the key for developing processing and imagingtechniques for our seismic look ahead prediction in tunnel constructions.Synthetic case studies have been used to investigate single propagation effects that occurunder tunneling conditions. For example, both the excavation damage zone and the lining of the tunnel wall significantly alters the dispersion characteristics of TS-waves. Furthermore, theexcitation and propagation of tunnel surface wave for the seismic look-ahead prediction in softrock and hard rock formations depends on the constraint of the resulting TS-wave wavelengthwith respect to the tunnel diameter. At the same time, these studies have been used to identifymodeling strategies and limitations of various finite difference modeling codes as well as semi-analytical solutions. Depending on the given problem, we can reduce the dimensionality of themodel and thus neglect certain wave propagation phenomena (e.g., 3-D geometrical spreadingand tunnel related dispersion) in order save computational time.i

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