TY - JOUR
T1 - A shear-wave seismic system using full waveform inversion to look ahead of a tunnel-boring machine
AU - Bharadwaj, Pawan
AU - Drijkoningen, Guy
AU - Mulder, Wim
AU - Thorbecke, Jan Willem
AU - Neducza, Boriszlav
AU - Jenneskens, R
PY - 2017
Y1 - 2017
N2 - In the near surface with unconsolidated soils, shear-wave properties can often be characterised better and with a higher resolution than compressional-wave properties. To enable imaging ahead of a tunnel-boring machine, we developed a seismic prediction system with a few shear-wave vibrators and horizontal receivers. The boring process is interrupted at regular intervals to carry out active surveys. The vibrators are then pushed against the rock or soil in front of the cutting wheel of the machine. The design of the vibrators is based on linear synchronous motor technology that can generate very low frequencies, starting at 5 Hz. These vibrators generate a force in a direction perpendicular to the tunnel axis. Horizontal receivers measure the particle velocity, mainly due to the horizontally polarised shear waves. Because imaging with conventional migration methods suffers from artefacts, caused by the incomplete aperture and inaccuracies in the assumed velocity model, we use two-dimensional horizontally polarised shear full-waveform inversion to resolve the subsurface shear properties. The classic cycle-skipping problem, which can make the application of fullwaveform inversion cumbersome, is avoided by the capacity of the vibrators to generate low frequencies. In this paper, we demonstrate the capabilities of the proposed seismic system through a number of synthetic and field experiments.
AB - In the near surface with unconsolidated soils, shear-wave properties can often be characterised better and with a higher resolution than compressional-wave properties. To enable imaging ahead of a tunnel-boring machine, we developed a seismic prediction system with a few shear-wave vibrators and horizontal receivers. The boring process is interrupted at regular intervals to carry out active surveys. The vibrators are then pushed against the rock or soil in front of the cutting wheel of the machine. The design of the vibrators is based on linear synchronous motor technology that can generate very low frequencies, starting at 5 Hz. These vibrators generate a force in a direction perpendicular to the tunnel axis. Horizontal receivers measure the particle velocity, mainly due to the horizontally polarised shear waves. Because imaging with conventional migration methods suffers from artefacts, caused by the incomplete aperture and inaccuracies in the assumed velocity model, we use two-dimensional horizontally polarised shear full-waveform inversion to resolve the subsurface shear properties. The classic cycle-skipping problem, which can make the application of fullwaveform inversion cumbersome, is avoided by the capacity of the vibrators to generate low frequencies. In this paper, we demonstrate the capabilities of the proposed seismic system through a number of synthetic and field experiments.
UR - http://resolver.tudelft.nl/uuid:6795ac4a-20b0-42da-86c3-3d5f7101d8eb
U2 - 10.3997/1873-0604.2017014
DO - 10.3997/1873-0604.2017014
M3 - Article
SN - 1569-4445
VL - 15
SP - 210
EP - 224
JO - Near Surface Geophysics
JF - Near Surface Geophysics
ER -