Accumulative Damage Effect of Interlaid Rock in Tunnel Groups with Small Clear Spacing

The blasting construction of narrow spacing tunnel inevitably causes accumulative damage of surrounding rocks and deteriorates its mechanics capability. The accumulative damage in the associated rock in tunnel groups are analyzed on the basis of dynamic damage variable and internal displacement combined with the monitoring results of Damaoshan tunnel. The study of sound wave velocity and internal displacement of surrounding rocks indicated that the newly-built blasting construction have caused damage, breakage and slippage in interlaid rock. Comparison of newly-built tunnel with existing tunnel reveals that accumulative damage caused by use of CRD technique is three times more than the same caused by use of whole section excavation. The upper section blasting causes the activation the fissure of rocks and declines sound wave velocity significantly. The vibration of inter-space rock caused by blasting of lower section is as same as wall vibration and causes rock loose and slide. The internal displacement of surrounding rock increases significantly. The rate of change of acoustic velocity and displacement amount should be taken into full consideration in analysis of range and degree of the accumulative damage in surrounding rocks.