Abstract In the hard-rock formations, Tunnel Boring Machines typically face challenges, such as low tunneling efficiency and severe cutter wear, which lead to prolonged construction periods and increased project costs. To address this issue, this study proposes a novel auxiliary technology that manufacture cracks by drilling and splitting on the tunnel face in advance, thereby reducing thrust and torque on the cutterhead and improving the cutting efficiency. To validate the effectiveness of this method, reduced TBM penetration tests on drilling–splitting specimens and numerical simulation based on ABAQUS were conducted. The spacing–depth ratio of boreholes (S/D), defined as the ratio of borehole spacing (S) to depth (D), was employed as the key index to systematically investigate cutting efficiency, rock-breaking modes, and fracture mechanisms under drilling–splitting conditions. The results indicate that when S/D = 0.86, the peak normal force reaches its minimum value of 5 kN, and the specific energy reaches its minimum value of 124.91 MJ/m3, corresponding to the highest cutting efficiency. With S/D increases from 0.70 to 1.29, the proportion of tensile cracks rises continuously from 47.4 to 89.3%, and the rock failure mode transitions from shear–compression-dominated cracking (S/D < 0.78), tensile–shear mixed cracking (0.78 ≤ S/D ≤ 1.00) to tensile-dominated cracking (S/D > 1.00). Three rock fragment modes are identified: prefabricated crack-dominated mode (S/D < 0.78), prefabricated crack–main crack cooperative mode (0.78 ≤ S/D ≤ 1.00), and main crack-dominated mode (S/D > 1.00). Numerical simulations further reveal that as S/D increases, stress concentration at the tip of the prefabricated cracks gradually weakens, while the stress concentration beneath the cutter intensifies. Consequently, the dominant roles of mode I (opening) and mode II (sliding) stress intensity factors (KI and KII) shift, leading to three cracking modes: compression–shear dominated, tensile–shear mixed, and tensile dominated. This study provides theoretical support for TBM tunneling technology in hard-rock formations, with practical significance for enhancing cutting efficiency and reducing cutter wear.

Experimental Investigation on the Effect of Spacing-Depth Ratio on the Breaking Mechanism of the Rock by TBM Cutter Assisted by Drilling–Splitting

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发表日期：

2025年12月24日

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Haowen Ruan,
Bolong Liu,
Minwei Lu,
Qinyuan Liang,
Huicai Gao,
Yong Niu,
Liang Zhang,
Guojiao Peng,
Wenfang Shi,
Zuoyong Qin

摘要

Abstract

In the hard-rock formations, Tunnel Boring Machines typically face challenges, such as low tunneling efficiency and severe cutter wear, which lead to prolonged construction periods and increased project costs. To address this issue, this study proposes a novel auxiliary technology that manufacture cracks by drilling and splitting on the tunnel face in advance, thereby reducing thrust and torque on the cutterhead and improving the cutting efficiency. To validate the effectiveness of this method, reduced TBM penetration tests on drilling–splitting specimens and numerical simulation based on ABAQUS were conducted. The spacing–depth ratio of boreholes (S/D), defined as the ratio of borehole spacing (S) to depth (D), was employed as the key index to systematically investigate cutting efficiency, rock-breaking modes, and fracture mechanisms under drilling–splitting conditions. The results indicate that when S/D = 0.86, the peak normal force reaches its minimum value of 5 kN, and the specific energy reaches its minimum value of 124.91 MJ/m³, corresponding to the highest cutting efficiency. With S/D increases from 0.70 to 1.29, the proportion of tensile cracks rises continuously from 47.4 to 89.3%, and the rock failure mode transitions from shear–compression-dominated cracking (S/D < 0.78), tensile–shear mixed cracking (0.78 ≤ S/D ≤ 1.00) to tensile-dominated cracking (S/D > 1.00). Three rock fragment modes are identified: prefabricated crack-dominated mode (S/D < 0.78), prefabricated crack–main crack cooperative mode (0.78 ≤ S/D ≤ 1.00), and main crack-dominated mode (S/D > 1.00). Numerical simulations further reveal that as S/D increases, stress concentration at the tip of the prefabricated cracks gradually weakens, while the stress concentration beneath the cutter intensifies. Consequently, the dominant roles of mode I (opening) and mode II (sliding) stress intensity factors (K_I and K_II) shift, leading to three cracking modes: compression–shear dominated, tensile–shear mixed, and tensile dominated. This study provides theoretical support for TBM tunneling technology in hard-rock formations, with practical significance for enhancing cutting efficiency and reducing cutter wear.