Locating scatterers while drilling using seismic noise due to tunnel boring machine

Unexpected geological structures can cause safety and economic risks during underground excavation. Therefore, predicting possible geological threats while drilling a tunnel is important for operational safety and for preventing expensive standstills. Subsurface information for tunneling is provided by exploratory wells and by surface geological and geophysical investigations, which are limited by location and resolution, respectively. For detailed information about the structures ahead of the tunnel face, geophysical methods are applied during the tunnel-drilling activity. We present a method inspired by seismic interferometry and ambient-noise correlation that can be used for detecting scatterers, such as boulders and cavities, ahead of a tunnel while drilling. A similar method has been proposed for active-source seismic data and validated using laboratory and field data. Here, we propose to utilize the seismic noise generated by a Tunnel Boring Machine (TBM), and recorded at the surface. We explain our method at the hand of data from finite-difference modelling of noise-source wave propagation in a medium where scatterers are present. Using the modelled noise records, we apply cross-correlation to obtain correlation gathers. After isolating the scattered arrivals in these gathers, we cross-correlate again and invert for the correlated traveltime to locate scatterers. We show the potential of the method for locating the scatterers while drilling using noise records due to TBM.Applied Geophysics and Petrophysic

Estimating the location of a tunnel using interferometric times of Rayleigh-wave scattering

Inspired by a technique called seismic interferometry, we estimate the location of a scatterer using scattered waves. We isolate the scattered wavefield and evaluate the result of correlating scattered waves at different receiver locations. The cross-correlation eliminates the travel path between a source and a scatterer, making the estimation of the scatterers’ locations dependent only on properties between the receivers and the scatterer. We illustrate the potential of this method by locating a tunnel from seismic 23 field data, recorded along a line with multiple source and receiver locations. As near-surface scatterers are potential weak zones and may pose risk for the environment, to mitigate geo- and environmental hazards, this method can be an efficient alternative in detection of such structures.Geoscience & EngineeringCivil Engineering and Geoscience

Locating scatterers by non-physical scattered waves obtained by seismic interferometry

The investigation and detection of near-surface structures (such as cavities, caves, sinkholes, tunnels, mineshafts, buried objects, archeological ruins, water reservoir, etc.) is important to mitigate geo- and environmental hazards. In a former study, we suggested a method based on active-source seismic interferometry for locating the scatterers and we showed the applicability of the method in a simple model. In our method, we use only one source at the surface and non-physical scattered waves retrieved by seismic interferometry to estimate the location of the scatterer. In this paper, we show the effectiveness of the method in case of lateral variations. We use both scattered body and surface waves to estimate the location of a corner diffractor and a scatterer, respectively, and we obtain very good estimations. The method is promising for near-surface seismic field applications.Geoscience and EngineeringCivil Engineering and Geoscience

Estimating the Location of Scatterers by Seismic Interferometry of Scattered Surface Waves

In this study, non-physical (ghost) scattered surface waves are used to obtain the location of a near surface scatterer. The ghost is obtained from application of seismic interferometry to only one source at the surface. Different locations for virtual sources are chosen and ghost scattered surface waves for each of these virtual-source locations are retrieved. The retrieved ghost traveltimes are inverted by solving the inverse problem to determine the location of the scatterer. It is seen that the location of the scatterer is reasonably well estimated.Geoscience & EngineeringCivil Engineering and Geoscience

Estimating the location of scatterers using correlation of scattered rayleigh waves

Inspired by a technique called seismic interferometry, we estimate the location of scatterers in a scaled model, where many near-surface scatterers are present. We isolate the scattered wavefield and evaluate correlation of scattered waves at different receiver locations. The cross-correlation eliminates the travel path between a source and a scatterer, making the estimation of the scatterers’ locations dependent only on properties between the receivers and the scatterer. We illustrate the potential of this method by locating scatterers with ultrasonic laboratory measurements of scattered Rayleigh waves recorded on two parallel and orthogonal lines of receivers. As near-surface scatterers are potential weak zones and may pose risk for the environment, to mitigate geo and environmental hazards, this method can be an efficient alternative that can be used in detection of such structures.Geoscience & EngineeringCivil Engineering and Geoscience

Estimating the location of a tunnel using correlation and inversion of Rayleigh wave scattering

The investigation of near-surface scatterers, such as cavities, tunnels, abandoned mine shafts, and buried objects, is important to mitigate geohazards and environmental hazards. By inversion of travel times of cross-correlated scattered waves, due to the incident Rayleigh waves, we estimate the location of a near-surface tunnel from seismic field data. The cross correlation eliminates the travel path between a source and a scatterer, thus eliminating the need to know the position of the source, making the estimation of the scatterers' locations dependent only on properties between the receivers and the scatterer. First time using a numerically verified method on seismic field data, we show the potential of the method for estimating the location of a buried scatterer.Geoscience & EngineeringCivil Engineering and Geoscience

Locating cavities using ghost scattered waves in a scale-model experiment

The investigation and detection of near-surface structures (cavities, caves, tunnels, mineshafts, buried objects, archeological ruins, water reservoir, etc.) is important to mitigate geo- and environmental hazards. We use a method inspired by seismic interferometry to estimate the location of a cavity in a scaled ultrasonic experiment, representative for geophysical field problems. We use only one source at the surface and retrieve ghost scattered waves by evaluating the correlation of scattered waves at different receiver locations. As an exploitation of the ghost arrival information, the ghost travel times are determined and combined to estimate the location of a cavity with good accuracy.Geoscience & EngineeringCivil Engineering and Geoscience