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| Experimental study on the mechanical properties of sandstone with different numbers of fractures before and after grouting |
| CHEN Juntao1，2，3，YU Junjian1，2，LI Guo1，3，XU Changlong1，2，FAN Mingjin1，3，WANG Yunhao1，3，JIAO Bin1，3 |
(1. College of Energy and Mining Engineering，Shandong University of Science and Technology，Qingdao，Shandong 266590，China；2. State Key Laboratory of Coal Mining and Clean Utilization，Beijing 100013，China；
3. National Demonstration Center for Experimental Mining Engineering Education，Shandong University of Science and Technology，Qingdao，Shandong 266590，China) |
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Abstract To investigate the influence of fracture number on the strength of rock before and after grouting，as well as the crack propagation patterns，an experimental study was conducted on the mechanical properties of sandstone with different numbers of fractures before and after grouting. The study combined XTDIC(Digital Image Correlation) and acoustic emission systems to examine crack propagation patterns from both macroscopic and microscopic perspectives. The experimental results showed that：(1) With an increase in the number of fissures，the time of the compaction stage in the stress-strain curve became shorter，and the crack development and propagation stage commenced earlier. The strength weakening coefficient exhibited a power function growth trend with the number of fissures，and the average compressive strength decreased by 15.82% to 53.32%. The strength recovery coefficient under a 1：1 water-cement ratio slurry showed an exponential decrease with the number of fissures，improving by 6.76% to 29.27% compared to the ungrouted state，reaching 60.34% to 89.88% of the original rock strength；(2) The number of fissures significantly impacted the crack initiation stress，which increased after grouting. The ratio of crack initiation stress to peak stress before and after grouting decreased with the increase in the number of fissures，showing a downward opening quadratic function relationship；(3) The crack propagation patterns before and after grouting with different numbers of fissures exhibited certain similarities. Cracks primarily developed from the fissure tips and connected prefabricated fissures before and after grouting，causing rock bridge penetration and predominantly tensile failure；(4) The AE ringing count and cumulative ringing count significantly increased with the number of fissures. Grouting could only improve the rock's overall integrity to a certain extent and suppress stress concentration at the tips but could not effectively prevent crack propagation and interaction；(5) Theoretical analysis indicated that the stress intensity factor after grouting was lower than before grouting，and KⅠgrouted＜KⅠ and KⅡgrouted＜KⅡ，suggesting that the stress at the fissure tips reduced after grouting，thereby enhancing the rock's strength. This was validated through numerical simulations.
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