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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, Pr) 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 Pr 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. Pr 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) Pr has a good linear correlation with coarseness index (CI) and specific energy (SE), the higher the TBM tunneling efficiency, the larger Pr and CI values, the less SE values; (3) Pr 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.

The construction environment of deep rock tunnels is complex, and effectively enhancing tunnel boring machine (TBM) tunneling efficiency is paramount. Increasing rock-breaking efficiency and minimizing cutter consumption are essential strategies for improving TBM tunneling efficiency. Selecting suitable tunneling parameters is crucial for enhancing rock-breaking efficiency and reducing cutter consumption. Existing research on the optimization of the ratio of maximum cutter spacing to penetration (Smax/P) based on field-measured data is limited, and few studies compare and analyze the relationship between SE, CI, and the Smax/P ratio separately. Consequently, this study determined optimal tunneling parameters for various types of surrounding rock and construction environments, aiming to more accurately optimize TBM tunneling performance during construction processes based on on-site construction data. This study conducted a comparative analysis of specific energy (SE) and the coarseness index (CI). Under both working conditions, the quadratic fitting coefficients of the CI are 4.2% and 10.6% higher than those of the SE, respectively, with the CI selected to represent the particle size distribution of rock chips. Finally, taking into account both the correlations between the CI and the ratio of maximum cutter spacing to penetration (Smax/P), as well as cutter consumption and the Smax/P ratio, an optimization method for the TBM tunneling parameter was established under both dry and saturated conditions. The research findings indicate that cutter consumption exhibits an exponential increase with a higher rock Cerchar Abrasivity Index (CAI); it initially decreases as the Smax/P ratio increases and subsequently increases in both dry and saturated conditions. Instead, the CI demonstrates an initial increase and subsequent decrease as the Smax/P ratio increases. Maximizing rock-breaking efficiency and minimizing cutter consumption are crucial for improving tunneling performance. In saturated conditions, the corresponding optimal Smax/P ratio ranges are 7.055–8.319 for soft rock, 8.606–8.931 for medium–hard rock, and 13.50–14.00 for hard rock, and these optimal ranges under dry conditions are 8.495–9.457, 10.972–12.169, and 16.5–17.5 for the same rock types. This study provides optimal Smax/P ratio ranges for TBM tunneling, thereby significantly enhancing tunneling efficiency.