Reinforcement effect of epoxy resin-polypropylene fiber cement grouting in repairing subway segments under SHPB impact loading

Composite grouting materials have been extensively utilized in construction engineering due to their exceptional ductility and toughness. Grouting is necessary for segment repair as the shield segments are prone to cracks caused by various environmental factors during subway operation. These segments often encounter shock loads, such as microshock and rock burst, due to repeated subway trips throughout their service life. This study employs the split Hopkinson bar technique (SHPB) to investigate the dynamic mechanical characteristics of tube segments under impact loading after grouting repair. Various factors, including different impact loads, buried depths, crack lengths, and numbers are taken into consideration. The results demonstrate that the incorporation of epoxy resin and polypropylene fiber enhances the ductility and densification of cement-based grouting materials, facilitating improved crack-filling capability. Moreover, an increase in the number of cracks leads to a decrease in sample strength, while peak stress and strain exhibit an upward trend with increasing impact loads, with maximum peak stress reaching 58.9 MPa. The peak stress and strain of the epoxy resin-polypropylene fiber cement (ERPC) grouting material are 1.05 times and 1.35 times those of the control group, respectively. The energy absorbed per unit volume also shows a positive correlation with impact loads. Specifically, the ERPC mortar achieves an average energy absorption of 560,000 J/m³ , with a 30.2 % enhancement compared with conventional cement mortar. Furthermore, the energy absorption per unit volume is highly sensitive to crack density and length. The present study offers theoretical support for using ERPC grouting material in the repair of shield segment structures, which holds significant engineering implications. • Conduct split Hopkinson pressure bar tests to study the impact resistance of subway segment repaired by epoxy-polypropylene fiber grouting. • Reveal the reinforcement mechanism of epoxy-polypropylene fiber grouting. • Analyze the dominant factors of different impact load, depth and cracks on the performance of grouting repaired concrete. • Propose the comprehensive performance evaluation methods and optimization suggestions for subway segment repaired by grouting.