Chapter 15: Gravity Mapping and Seismic Imaging of Paleochannels on Large Tunnel Routes in Sydney, Australia
Governments and municipal authorities, faced with the problems of providing infrastructure within and between densely populated megacities, are increasingly recognizing the importance of tunnels for installation of underground transport corridors, sewerage systems and utilities. Many tunnels are now completed with advanced mechanical tunnel boring machines (TBMs) that are displacing the older drill and blast methods. TBMs can excavate a full circular face to the diameter of the machine, typically from 2 to 12 m, at astonishingly rapid rates when rock mass conditions are excellent. Even so, and despite dramatic improvements in TBM technology (Biggart, 1999), TBMs are still not good at coping with rapidly changing or poor geologic conditions that can slow or stop the machines, increasing risks and costs to the tunnel project (Mitani, 1998).
Figures & Tables
Near-surface geophysics uses the investigational methods of geophysics to study the nature of the very outermost part of the earth’s crust. Man interacts with this part of the earth’s crust: he walks on it; he drills and excavates into it; he constructs structures on and in it; he utilizes its water and mineral resources; and his wastes are stored on and in it and seep into it. The very outermost part of the Earth’s crust is extremely dynamic-in both technical (physical properties) and nontechnical (political, social, legal) terms-which leads to both technical and nontechnical challenges that are much different than the challenges faced by “traditional” applications of geophysics for regional geologic mapping and for oil and gas exploration (see Chapter 2).