Exploration Ahead of a Tunnel Face by TSWD – Tunnel Seismic While Drilling

Abstract

Geological and geophysical investigations, as well as drilling have brought the quality of geotechnical prognosis for tunnels to a high standard. However, the remaining risk during tunnel construction is still considerable, especially in case of construction by a tunnel boring machine (TBM). Seismic imaging of faults and other geological features affecting the construction ahead of a tunnel face can supply valuable information to reduce this risk. These methods are based on Vertical Seismic Profiling (VSP) locating sources and receivers in the tunnel and generating seismic waves by small blasts or mechanical devices. A fundamental problem in the application of this method is that reflectors (fault zones, petrologic boundaries, or similar) are imaged at their intersection with the tunnel axis only in case they are orthogonal to this axis. Reflectors oriented obliquely to the tunnel axis may be imaged perfectly. However, they must be extrapolated to their intersection with the tunnel axis, thus imposing major uncertainties on prediction.Therefore it was decided to concentrate on Tunnel Seismic While Drilling (TSWD), an alternative method, which uses the vibrations produced by the cutting head of the TBM as seismic source. Continuous monitoring is possible by this method and the above mentioned problem may be overcome. Conventional seismic traces are extracted from the recordings by the use of a pilot signal recorded near the cutting head of the TBM. First results from a pilot study accompanying the construction of a gallery in the Gesäuse mountain range, Styria, Austria are presented. The bandwidth of the seismic signals is >200 Hz, a high signal to noise ratio is achieved, and excellent conventional seismic traces are extracted. Thus the most important component of the whole method has been realised successfully. Additional aspects of the method are discussed and an outlook to the continuation of the pilot study is given.

Prediction of tunneling hazardous geological zones using the active seismic approach

“…The tunnel‐seismic‐while‐drilling method makes use of the vibrations produced by the cutting head of the TBM as a seismic source (Petronio, Poletto, and Schleifer ; Bruckl et al . ). The main advantage of these methods is the acquisition of real‐time information on the rock characteristics ahead of the TBM, without interference with drilling (Poletto and Petronio ; Kneib ).…”

Detection of geological structures using impact‐driven piling as a seismic source

“…Brückl et al . () used a tunnel boring machine (TBM) as a seismic source. The vibrations produced by the cutting head of the TBM were used for seismic imaging.…”

“…Rector's (1990) results demonstrated high correlation between the drill bit VSP and conventional VSP images and a good tie to the surface seismic image. Brückl et al (2008) used a tunnel boring machine (TBM) as a seismic source. The vibrations produced by the cutting head of the TBM were used for seismic imaging.…”

Seeing coal‐seam top ahead of the drill bit through seismic‐while‐drilling

“…Conceptually, any kind of mechanical vibration that is activated in the subsurface can be used as the source for seismic imaging (Hardage 2009). Tunnel boring machines have been used for imaging geological hazards ahead of a tunnel face (Sattel, Frey, and Amberg 1992;Petronio and Poletto 2002;Poletto and Petronio 2006;Petronio, Poletto, and Schleifer 2007;Brückl et al 2008;Dickmann 2008;Lüth, Gies, and Rechlin 2008). Mining machines have been used as seismic sources for inseam reflection mapping ore-zone discontinuities in a potash mining environment (Taylor et al 2001).…”