Key Takeaways & Executive Findings
- •• Laser-induced fracturing of limestone, sandstone, and granite reveals distinct failure modes: tensile-shear composite in limestone, tensile in sandstone and granite. • Sandstone and granite exhibit lower acoustic emission peak energy due to melt dissipation, while larger specimens delay peak energy occurrence. • Fracture surface roughness (JRC and fractal dimension) is highest in sandstone, with asperity heights of 1–14 mm and slope angles up to 40°. • Granite shows the highest macropore proportion (~4.8%) post-irradiation, indicating significant porosity changes.
Abstract
For hard rock cracking induced by laser irradiation, the failure modes and fracture characteristics among rocks of different types and sizes are still unclear. Therefore, the experiments on laser-induced fracturing of limestone, sandstone, and various-sized granite specimens were conducted. Real-time acoustic emission monitoring and laser scanning were employed to capture acoustic emission signals inside rocks during laser irradiation and to reconstruct the fracture surfaces after laser irradiation. Results indicate that abundant melts in sandstone and granite dissipated laser energy, leading to lower acoustic emission peak energy compared to limestone. Larger-sized specimen delayed the occurrence of peak energy. Crystal thermal expansion and changes in pore pressure induced tensile-shear composite failure in limestone, whereas thermal expansion of minerals in sandstone and granite promoted tensile failure. Fracture surface morphology was influenced by sampling interval, anisotropy, and size effects. The joint roughness coefficient and fractal dimension of sandstone exceed granite and limestone. Asperity heights and slope angles ranged from 1–14 mm and 0–40°, respectively, with the average aspect angles exceeding 110°. Granite exhibited the highest proportion of macropores after laser irradiation, approximately 4.8%. These findings provide valuable insights for the application of laser-assisted fracturing in hard rock excavation.
1. Introduction
Tunnel boring machines (TBMs) serve as the primary mechanism for hard rock excavation during tunneling. However, when dealing with high-strength rock masses, TBMs encounter significant challenges, including elevated specific energy requirements, diminished advance rates, pronounced cutter wear, and construction delays. These issues not only escalate operational costs but also heighten project risks [1]. For example, in the Floskefonn Tunnel (Norway), rock exhibiting a compressive strength of 270 MPa decelerated the TBM’s advance rate to a mere 0.5 m/h [2]. Similarly, in the Qinling Water Diversion Tunnel (China), rocks with a compressive strength reaching up to 325 MPa curtailed advance rates to 1.2 m/h, resulting in monthly progress of less than 170 m [3]. Analogous challenges have been documented in India, South Africa, and Turkey [2]. Consequently, tunneling through such exceptionally hard rock formations presents a formidable global challenge in the realm of deep underground engineering. There is an imperative need to innovate rock fragmentation technologies tailored for these demanding formations.
The development of advanced rock-breaking methodologies is critical for overcoming issues including low advance rates, accelerated cutter wear, and high costs in high-rock excavation [4]. Numerous innovative rock-breaking technologies are under extensive investigation, including microwave, water-jet, and laser [3]. Among these, laser fracturing technology is perceived as a promising alternative due to its non-contact method and environmentally friendly advantages [5]. This technology converts electrical energy into thermal energy, which is then concentrated on the rock surface. This generates intense thermal effects, inducing the weakening, fragmentation, melting, and gasification of rock minerals. These processes generate new free surfaces that reduce their fragmentation resistance. Studies have demonstrated
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Dongxu Yu, Yijiang Wang, Shuchen Li, Zongheng Jiang, Jianzhou Wang (2025). Experimental investigation on failure mode and fracture characteristic of rock samples induced by laser irradiation. SinoTechIntel Verified Research. https://doi.org/10.1016/j.ijmst.2025.10.001
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Frequently Asked Questions
What are the main failure modes of rocks under laser irradiation?
Limestone exhibits tensile-shear composite failure due to crystal thermal expansion and pore pressure changes, while sandstone and granite primarily undergo tensile failure from mineral thermal expansion.
How does rock type affect acoustic emission during laser irradiation?
Sandstone and granite produce lower acoustic emission peak energy compared to limestone because abundant melts dissipate laser energy.
What is the effect of specimen size on laser-induced fracturing?
Larger specimens delay the occurrence of peak acoustic emission energy, indicating size effects on fracture dynamics.
Which rock type shows the highest fracture surface roughness after laser irradiation?
Sandstone exhibits the highest joint roughness coefficient and fractal dimension, with asperity heights ranging from 1–14 mm and slope angles up to 40°.
How does laser irradiation affect pore distribution in rocks?
Granite shows the highest proportion of macropores after laser irradiation, approximately 4.8%, indicating significant porosity changes.
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