Investigation of structures in tunnel overburdens by means of muon radiography

Cosmic ray muon radiography is a new imaging technique that is being used to investigate the density structure of large objects and the shallow crust. For example, it has been used to investigate magma conduits of active volcanoes, cavities above tunnels and hidden chambers inside pyramids, and has proven to be effective and accurate. However, low cosmic muon flux has limited the development of muon radiography in many engineering applications. In this paper, the potential application of muon radiography to investigate density anomalies in tunnel overburden is discussed. Results show that in a typical 25-meter thick overburden, muon radiography can identify overburden anomalies of 10% in two hours with an inaccuracy probability of 30.8% by lack of enough statistics, and this inaccuracy will reduce to 2.2% if data are collected over a full day. The study also indicates that muon radiography can detect structure density anomalies above 1% with an inaccuracy probability of 2.2%. As a non-destructive, non-invasive and passive imaging method, cosmic ray muon radiography has its great potential in timely monitoring and imaging of overburden structures to discover potential structural defects.