Realistic FD modeling of the tunnel environment for seismic tomography

To improve the safety both of the tunnel constructions and buildings at the surface, seismic tomography methods can be used to detect possible safety threads behind the tunnel wall (e.g. cavities, water bearing zones, fractures). Basis for such a tomography is a profound understanding of the seismic wave propagation in the complex surrounding of a tunnel which can be gained from seismic modeling We, therefore, created a realistic tunnel model that accounts for typical features encountered during tunnel construction, e.g. heterogeneous host rock, excavation damaged zone (EDZ) and topography of the tunnel wall. This model is used for the 3-D elastic wave field simulations. Data from multiple shot positions will be later on used for a seismic tomography, either by standard travel time tomography or full waveform tomography. Main objective is the accurate seismic modeling using optimal discretization parameters and an implicit free surface boundary with topography

Seismic prediction and imaging of geological structures ahead of a tunnel using surface waves

To improve the performance and safety of tunnel constructions, we introduce a new seismic prediction method utilizing tunnel surface waves to detect relevant geological structures ahead of the tunnel face. On the basis of both synthetic and field data, we investigate the propagation characteristics of such surface waves propagating along the tunnel wall. We further introduce a simple but robust automatic prediction scheme that can estimate the distance to a reflector ahead of the tunnel

Bestimmung des Tongehaltes aus verschiedenen Log in ausgewählten Abschnitten der Bohrung Boetersen Z5a

Am Beispiel der Bohrdaten der Bohrung Boetersen Z5a wurde mit dem Modul PetroViewPlus der Schlumberger Software GeoFrame der Tongehalt bestimmt. Als Tonindikatoren kamen das das integrale und spektrale Gamma, das SP, das Neutron und das Sonic Log zum Einsatz. Die Ergebnisse der Tongehaltsbestimmung auf diesen vier Wegen wurden ermittelt, verglichen und versucht zu verfeinern

Realistic FD modeling of the tunnel environment for seismic tomography

To improve the safety both of the tunnel constructions and buildings at the surface, seismic tomography methods can be used to detect possible safety threads behind the tunnel wall (e.g. cavities, water bearing zones, fractures). Basis for such a tomography is a profound understanding of the seismic wave propagation in the complex surrounding of a tunnel which can be gained from seismic modeling We, therefore, created a realistic tunnel model that accounts for typical features encountered during tunnel construction, e.g. heterogeneous host rock, excavation damaged zone (EDZ) and topography of the tunnel wall. This model is used for the 3-D elastic wave field simulations. Data from multiple shot positions will be later on used for a seismic tomography, either by standard travel time tomography or full waveform tomography. Main objective is the accurate seismic modeling using optimal discretization parameters and an implicit free surface boundary with topography

Detection of geological structures ahead of the tunnel construction using tunnel surface-waves

To improve the performance and safety of tunnel constructions, seismic predictions methods can be used to detect relevant geological structures ahead of the tunnel face (e.g. faults, lithological boundaries). We present a simple and robust processing method that can automatically calculate the distance of such a geological inhomogeneity from the seismic response of only a few receivers mounted on the tunnel wall. The method works fully automatic and does need much computational resources which is ideal under tunneling conditions. Our approach has been develop on 3D synthetic finite difference and tested on real tunneling data. In both cases, the distance of a fault zone has been determined accurately and without any a priori information

Seismic prediction ahead of tunnel construction using Rayleigh-waves

To increase safety and efficiency of tunnel constructions, online seismic exploration ahead of a tunnel can become a valuable tool. We developed a new forward looking seismic imaging technique e.g. to determine weak and water bearing zones ahead of the constructions. Our approach is based on the excitation and registration of tunnel surface-waves. These waves are excited at the tunnel face behind the cutter head of a tunnel boring machine and travel into drilling direction. Arriving at the front face they generate body-waves propagating further ahead. Reflected S-waves are back-converted into tunnel surface-waves

Seismic prediction ahead of tunnel construction using tunnel surface-waves

To increase safety and efficiency of tunnel constructions, online seismic exploration ahead of a tunnel can become a valuable tool. We developed a new forward looking seismic imaging technique to e.g. determine weak and water bearing zones ahead of the constructions. Our approach is based on the excitation and registration of tunnel surface-waves (TS-waves). These waves are excited at the tunnel face behind the cutter head of a tunnel boring machine and travel into drilling direction. Arriving at the front face they generate body-waves (mainly S-waves = ”RS”-waves) propagating further ahead. Reflected S-waves are back-converted into tunnel surface-waves (”RSSR”-waves) and can be recorded by geophones mounted on the tunnel wall. Using 3D Finite Difference modeling, an analytical solution of the wave equation in cylindrical coordinates and field data acquired at the Gotthard massive (Switzerland) we investigated the propagation characteristics of tunnel surface waves in terms of dispersion and polarization. Understanding the excitation and propagation of TS-waves is the key for developing processing and imaging techniques for our seismic look ahead prediction in tunnel constructions

Rayleigh-to-shear wave conversion at the tunnel face - from 3D-FD modeling to ahead-of-drill exploration

For a safe tunnel excavation it is important to predict lithological and structural heterogeneities ahead of the construction. conventional tunnel seismic prediction systems utilize body waves (P- and S-waves) that are directly generated at the tunnel walls or near the cutter head of the tunnel boring machine (TBM). In this work we propose a new prediction strategy that has been discovered by 3-D elastic finite-difference (FD) modeling: Rayleigh waves arriving at the front face are converted into high amplitude S-waves propagating further ahead. Reflected or backscattered S-waves are converted back into Rayleigh waves which can be recorded along the side walls. We name these waves RSSR waves. In our approach the front face acts as a S-wave transceiver. One technical advantage is that both the sources and the receivers may be placed behind the cutter head of the TBM. The modeling reveals that the RSSR waves exhibit significantly higher amplitudes than the directly reflected body waves. The excavation damage zone causes dispersion of the RSSR wave leading to multi-modal reflection response. For the detection of geological interfaces ahead RSSR waves recorded along the side walls are corrected for dispersion and stacked. From the arrival times the distance to the S-S reflection point can be estimated. A recurrent application, while the tunnel approaches the interface, allows one to quantify the orientation of the reflecting interfaces as well. Our approach has been successfully verified in a field experiment at the Piora adit of the Gotthard base tunnel. The distance to the Piora fault zone estimated from stacked RSSR events agrees well with the information obtained by geological surveying and exploratory drilling

Seismic prediction ahead of a tunnel face - Modeling, field surveys, geotechnical interpretation

An important precondition for underground construction is a detailed knowledge of the soil and/or rock conditions in the area of the construction. In order to overcome existing limitations in classical exploration methods, research and development for exploration ahead of a tunnel face focuses on: hardware development for excavation integrated measurements, modelling and processing of data measured under these specific circumstances, and integrative interpretation of seismic results with other data from the excavation, from geological mapping, and from exploratory drilling, where available. Finite difference modelling of seismic wavefields around tunnels has shown the general feasibility of seismic measurements for imaging structures ahead of a tunnel face. The modelling results were confirmed by field measurements in various tunnel sites. The integrated interpretation of seismic data with all available geological and geotechnical information is currently in the state of development and aims, in the middle to long term perspective, at an “a priori” detection of structures ahead of the face