Development of a quantitative risk assessment method to address the rock mechanics issues of applying TBMs in deep mines

Roohollah Narimani Dehnavi

Research output: ThesisDoctoral Thesis

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For fast roadway development in deep underground mining, Tunnel Boring Machines are sometimes brought into operation. However, such machines might get entrapped if squeezing behavior develops and the machine advance rate is not high enough because of breakdowns. This research investigates the suitability of different types of Tunnel Boring Machines for development of infrastructure in deep mines and tunneling projects, with an emphasis on geological risks including squeezing and rockburst. The main consequences linked to these hazards are identified as worker injuries and support system and equipment damage in regions susceptible to rockbursts, and occurrences of shield jamming, support system damage, and challenges related to gripper bracing in squeezing grounds. In pursuit of the primary objective of this research, a probabilistic approach is used to quantitatively assess these consequences, leading to the development of an index called the TBM Risk Index, which assesses the cumulative effect of geological risks and mitigating measures. To conduct an initial evaluation of shield jamming, as the most critical consequence in squeezing scenarios, a combination of parametric studies based on pre-conducted 3D numerical models and an approach derived from convergence confinement (CC) concept were used. The adapted convergence confinement method was also employed to assess the risk of support system damage. As for the rockburst consequences, the procedure highly relies on factors such as rockburst intensity and location, which are notably challenging to anticipate. To analyze these risks, preliminary rockburst prediction tools together with a probabilistic approach based on data from a relevant project were applied. The methodologies introduced in this research were implemented in two primary case studies, each focusing on a specific category of geological risks, leading to the following key findings: The case study with only squeezing consequences highlighted the effectiveness of a single-shielded TBM with shield lubrication in mitigating the risk. On the contrary, the case study with rockburst hazards demonstrated the higher risks associated with shorter shields in rockburst-prone areas. Recognizing the uniqueness of each individual project, the research considered multiple hypothetical scenarios with varying proportions of squeezing grounds, areas susceptible to rockbursts, and regions characterized as normal grounds. Using the introduced TBM risk index, insights were gained for an optimum decision to be made between different available machines and mitigating measures. In scenarios with both squeezing and rockburst risks of roughly the same percentage, a single-shielded TBM with lubrication and a gripper TBM with associated mitigating measures were shown to have the lowest extent of rock mechanics issues. When rockburst risk is predominant, shielded TBMs are the preferred option, reducing exposure to seismic events. In scenarios with predominant squeezing grounds, gripper TBMs had the lowest TBM risk index. However, it is noteworthy that in severely squeezing grounds with prevalent squeezing proportion, the application of TBMs are generally questionable and conventional tunneling must be considered instead.
Translated title of the contributionEntwicklung einer quantitativen Risikobewertungsmethode zur Bewältigung der Gebirgsmechanikprobleme bei der Anwendung von Tunnelbohrmaschinen (TBMs) in tiefen Bergwerken
Original languageEnglish
Awarding Institution
  • Montanuniversität
  • Villeneuve, Marlene, Assessor A (internal)
  • Bruland, Amund, Assessor B (external), External person
  • Sifferlinger, Nikolaus August, Supervisor (internal)
  • Rostami, Jamal, Co-Supervisor (external), External person
Publication statusPublished - 2024

Bibliographical note

no embargo


  • TBM risk index
  • Squeezing
  • Rockburst
  • shield jamming
  • Probabilistic approach

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