RETRACTED: Study on dynamic characteristics and energy evolution of cement mortar-granite composite layer using SHPB under different temperatures up to 800 ℃

In tunnel engineering, composite-layered support systems, formed by the lining and surrounding rock, can experience fire and explosive loading from transient catastrophic events throughout their operational lifespan. Understanding the dynamic mechanical responses and energy-dissipation laws of structures after exposure to high temperatures is essential to preventing accidents and facilitating post-disaster restoration. In this study, a Split Hopkinson Pressure Bar (SHPB) test system with heating function is employed to conduct dynamic impact tests on cement mortar-granite (CMG) composite layer under different temperatures up to 800 ℃. The dynamic mechanical properties and energy-evolution mechanisms of the composite layer are systematically analyzed in relation to high temperatures and impact rates. The results indicated that the dynamic compressive strength (DCS) of the composite layer exhibited a clear strain-rate dependency. The variation in the dynamic increase factor (DIF) was significantly influenced by the competition between the temperature and strain rate. As the temperature and impact rate increased, the damage morphologies of the granite and cement mortar became more distinct. At 200 ℃, the structural integrity of the composite layer improved, and the fractal dimension exhibited a "z" trend, initially increasing and then decreasing, and finally increasing again. At temperatures over 200 ℃, specific energy absorption (SEA) and energy-consumption rate of the composite layer significantly decreased. Equivalent wave impedance (EWI) of the composite layer was very sensitive to temperature, but less sensitive to the impact rate. At high temperatures, the wave-attenuation ability of the composite layer was enhanced, more incident energy was converted into reflected energy, and the proportions of the transmission and destruction energies were reduced.