Experimental and numerical studies of the effects of micro/nano carbon fibers in the dynamic behavior of cement-based grouting materials for reinforcement of sand layers

Geological hazards of sand layers pose a serious threat to engineering safety. Grouting reinforcement technology is widely used in such conditions due to its convenience, economy, and effectiveness. To explore the reinforcement effect of carbon fiber (CF) modified cement-based grouting materials on sand layers, grouting solidified bodies (GSB) with CF contents of 0.0%, 0.5%, 1.0%, and 1.5% are selected for Split Hopkinson Pressure Bar (SHPB) impact tests, scanning electron microscope (SEM) scanning, and numerical simulation experiments. The mechanical properties of specimens under dynamic impact conditions and the reinforcement mechanism of CF are studied. Results show that GSB is a strain-rate-dependent material. With the increase of impact rate, peak stress, incident energy, transmitted energy, and dissipated energy of specimens gradually increase, while the integrity of specimens decreases. The CF content remarkably affects the mechanical properties of specimens. When the impact rate is constant, with the increase of CF content, the peak stress and transmitted energy of specimens show a decreasing-increasing- decreasing trend, and the performance of CF-1.0% specimens is optimal. The cement matrix is the main energy storage and release medium, accounting for 97.66% of the energy. When damaged, the cement matrix is mainly fractured. At the microcrack tip, CF influences the direction of crack propagation, reducing the radius of crack propagation, and the main failure mode of CF is debonding. CF can substantially improve the mechanical properties of specimens and reduce the number of cracks. Compared with CF-0.0%-cementitious material (CM) specimens, the peak stress of CF-1.0%-CM specimens is increased by 19.98%. The magnitude of CF force is related to the angle between crack and CF. As the angle increases from 0 degrees to 90 degrees, the CF force gradually increases, reaching the maximum at 90 degrees, with an increase of 133.82%. At this angle, the anti-cracking effect of CF is most substantial. The research results can provide technical support for sand layer grouting reinforcement technology.