Dynamic tensile behavior of fiber-reinforced sandy clay treated with alkali-activated metakaolin cement

Due to intense geological dynamics and human activities in coastal underground engineering, it is crucial to investigate the dynamic tensile strength and energy absorption capacity of fiber-reinforced sandy clay treated with alkali-activated metakaolin (AAMK) cement used as backfill. Dynamic indirect tensile tests were conducted using a Split Hopkinson Pressure Bar (SHPB) on mixtures with varying sand, fiber, and polymer contents. Dynamic tensile behavior, energy absorption density, and energy absorption rate were evaluated. Microstructural evolution before and after impact was observed by SEM, and fractal analysis of fragment size distribution n was used to characterize damage. Results show that when the strain rate increased by 6.05%, the residual strain rose by 9.30%. The maximum dynamic tensile strength (0.49 MPa) occurred at 12% sand and 0.2% fiber. Fiber inclusion increased energy absorption density by about 34%–145% compared with fiber-free specimens. With sand content increasing from 12% to 16%, the fractal dimension rose by 26.0% (1.663–2.095). A mix with 12% sand and ≥0.2% fiber is recommended as an economical and practical optimal ratio for engineering applications.