Identifying Effective Rock-Breaking Ratio Based on Rock Chip Information for Rock-Breaking Efficiency Evaluation of TBM

The rock chip information (shape, size, and particle size distribution) could comprehensively reflect the characteristics of rock mass and rock-breaking efficiency of TBM. This study is aimed at defining a novel index (effective rock-breaking ratio, $P_{\text{r}}$ ) to identify the rock-breaking efficiency of TBM based on the rock chip information. To evaluate this approach, a series of field sieving and measuring tests of rock chips was conducted at the water conveyance tunnel construction projects of China. The rock-breaking efficiency evaluation and tunneling parameter improvement of TBM were researched based on $P_{\text{r}}$ index. The results showed as follows: (1) from the perspective of energy conversion, the rock chip surface area was calculated through the rock chip cumulative volume distribution model. $P_{\text{r}}$ is used to evaluate the rock-breaking efficiency of TBM based on the proportion of surface area of rock chips with particle size larger than 5 mm; (2) $P_{\text{r}}$ has a good linear correlation with coarseness index (CI) and specific energy (SE), the higher the TBM tunneling efficiency, the larger $P_{\text{r}}$ and CI values, the less SE values; (3) $P_{\text{r}}$ increases at first and then decreases with the rise of thrust force of TBM. The optimal thrust force intervals for grade II and III surrounding rocks can be determined to improve the rock-breaking efficiency of TBM. Findings from this study are insightful in terms of accurately evaluating the excavation efficiency and improving the tunneling parameters of TBM.