Relationships between tunneling parameters of TBM and rock chip characteristics based on image analysis

Image analysis of rock chips is an important approach for TBM intelligent tunneling, and it can be used for real-time evaluation of rock-breaking efficiency and optimization of tunneling parameters. In order to investigate the relationships between TBM tunneling parameters and rock chip characteristics, a multi-step field tunneling test was carried out in an intact granite formation at a TBM construction section of Qingdao Metro Line 6. A rock chip image acquisition system was installed on the TBM to real-time collect rock chip images. Then, the relationship between the tunneling parameters and the size and shape characteristics of rock chips obtained through image processing was analyzed. The results showed that the median particle size d₅₀, maximum particle size d_max and roughness index CI all present a positive correlation with thrust, torque and penetration, while a good negative correlation with FPI and SE. When the thrust exceeds a critical value for rock-breaking, the increase in thrust will significantly increase d₅₀ and CI, while d_max increases significantly only when the thrust exceeds a larger value. Besides, as the thrust increases, the shape of the large rock chips gradually becomes flattened and the aspect ratio increases. However, after the thrust reaches a certain level, the aspect ratio will remain stable. The results can provide a basis for real-time optimization of TBM tunneling parameters based on rock chip information.