To investigate the effects of joint number on dynamic compressive strength, crushing effect, stress wave propagation, stress wave conversion, and energy evolution of rock masses, SHPB and LS-DYNA were used to conduct impact experiments and numerical simulations, respectively. The results demonstrate that the dynamic strength of a multi-jointed (two- and three-jointed) rock are 11.1 and 25.1% lower, respectively, compared with that of a single-jointed rock. The weak surface near the joint causes the rock mass to crack first. The rock cracking time advances significantly as the joints number increases. The reflection coefficient falls as the number of joints increases, because the wave impedance of the joint differs from that of the rock. The transmission coefficient, however, is exactly the reverse. When the P wave strikes the specimen, the vibration direction of the particles is deflected at the joint, resulting in a shear wave. P waves are reflected and superimposed between joints, increasing the strength of shear waves and resulting in more transverse cracks in multi-jointed rock masses under dynamic loading. Meanwhile, the total energy consumed by a bedrock under dynamic loading is obviously larger than that of joints. However, the total energy absorbed by joints exceeds that of the bedrock when the joints number increases. The results further enrich the dynamic basis of jointed rock masses.

To investigate the dynamic mechanical properties and fracturing behavior of the red sandrock-polypropylene fiber reinforced concrete (R-PPFRC) composite, R-PPFRC composite specimens with different Polypropylene fiber (PPF) dosage were fabricated. Conducted quasi-static compression experiments and dynamic experiments by using Split Hopkinson pressure bar (SHPB) apparatus and testing machine. The fracture characteristics and process of composite specimens were analyzed with the assistance of ultra-high-velocity camera photography. It can be concluded that the dynamic increase factor and the dynamic compressive strength of composite specimens R-PPFRC increase with the increase of load level, indicating a remarkably strain rate strengthening effect. The optimal PPF content is determined finally. The dynamic impact toughness, ultimate toughness, and dissipation energy of R-PPFRC are significantly affected by the load level and the PPF content. The fracturing process of the composite specimen is divided into four phases, crack initiation, crack expansion, crack cluster and ultimate failure. After going through these phases, the ultimate failure pattern is mainly shear and split mixed failure.