Dynamic Response and Cumulative Damage of Rock Mass Under Cyclic Blasting Load

Understanding the dynamic response and cumulative damage of rock mass caused by cyclic blasting load is critical for ensuring construction safety. With reference to the Nanhuo extra-long tunnel within the Chengde-Pinggu section of the Capital Circle Expressway, an analysis of the cumulative damage and dynamic response of a large-section tunnel subjected to cyclic blasting was performed using MIDAS-GTSNX software. The findings revealed that the angle of the explosion stress wave varies during its propagation in both the transverse and longitudinal directions. The peak transverse vibration velocity was observed at the inverted arch, while the peak vertical vibration velocity occurred near the vault, suggesting that vertical damage was more severe. After five cycles of blasts, the displacement and velocity of rock mass exhibited a cumulative effect, with section c-c experiencing the greatest damage. Following the first cycle of blasts, stress concentration was primarily observed at the arch edge and arch foot, with a notable reduction in stress concentration during subsequent blasts. Therefore, monitoring of the arch edge and arch foot should be strengthened during the construction process.