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EGU21-9667
https://doi.org/10.5194/egusphere-egu21-9667
EGU General Assembly 2021
© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.
Cosmic-ray muography applications in underground tunnelling
Pasi Kuusiniemi1,2, Marko Holma1,2,3, and Zongxian Zhang4
1Muon Solutions Oy, Pyhäsalmi, Finland (pasi.kuusiniemi@muon-solutions.com)
2Arctic Planetary Science Institute, Äänekoski, Finland
3Kerttu Saalasti Institute, University of Oulu, Nivala, Finland (marko.holma@oulu.fi)
4Oulu Mining School, University of Oulu, 90014 Oulu, Finland
The novel geophysical remote imaging method of muography is based on cosmic-ray induced
muon particles that are detected after passing through the media of interest. If the studied objects
are solid, their sizes can vary from meters to up to kilometres. In terms of penetration capability,
muography can be placed between methods based on X-rays and those using seismic waves. The
most famous objects imaged with muography are pyramids (e.g., Khufu's Pyramid at Giza in Egypt)
and volcanoes (e.g., Mt Etna in Italy). One clear advantage of muography compared with seismic
methods is that muons, unlike seismic waves, do not reflect from geological interfaces. In addition,
the scattering phenomenon is a minor issue and needs consideration only at low-energy muons.
Raw data must be corrected according to topography. On the basis of extensive numeric
simulations of Hivert et al. (2017), the lowest density variations observable for muography with a
significant level of 3σ (a typical significance level in physics) are around 2% at 150 m, 4% at 300 m,
and 10% at 700 m of depth, respectively. If these numbers are extrapolated to depths below 100
m, the mean density differences in the range of 1% are likely within the observation capability of
muography. It is also worth to note that the 1% difference in a mean rock density results in an
approximately 3% difference in the muon flux. This indicates that muon flux measurements are
very sensitive to the density variations of rocks.
In underground tunnelling, muography has at least four applications: (1) muography can be used
to detect a potential risk (such as a water reservoir, a weak zone with loose rocks, boulders, etc.)
before or during tunnelling, (2) muography can be employed to monitor overburden rock
behaviour during tunnelling operation to avoid risks like the roof cave-ins, (3) muography can be
applied to monitor the overburdening rock masses in tunnels after they are excavated to predict
and avoid the collapse of rock mass, and (4) muography can be used to estimate the size and
volume of a rock mass collapse in a tunnel since the volume of the collapsed rocks must have
markedly smaller density than original overburden rock mass. In an excavating tunnel project
using a tunnel boring machine (TBM), a muon detector can be installed in the TBM during
tunnelling. If there occurs a tunnel cave-in, muography can be employed in undamaged tunnels
nearby (sideways or below) the collapse. If possible, the collapse can also be approached safely via
an undamaged part of the collapsed tunnel. If none of these are available, borehole muography
can be applied as a substitute solution. Whereas an undamaged underground tunnel is either
