Failure characteristics of tunnel under the true triaxial condition: Role of a prefabricated flaw

Flaws such as faults, joints, and bedding planes often exist in natural rock masses, which pose significant safety hazards for tunnel excavation. We conducted a series of experimental tests to analyse the effect of the different flaw occurrences (intact, open-flaw, and filled-flaw) on the rockburst mode around a horseshoe-shaped tunnel. The destruction was monitored by continuous photo imaging (captured inside the tunnel) and acoustic emission (AE) monitoring. Test results show that: 1) Under different flaw occurrences, the rockburst mode is different. mainly for strain rockburst and fault slip rockburst 2) Strain rockburst produces more tensile cracks in the initial stage (I and II) and more shear cracks in the later stage (III, IV and V). However, the fault slip rockburst produces shear cracks from the beginning to the end. 3) The filled material inside the flaws can significantly enhance the stability of the surrounding rock and also inhibit the development of fault slip rockburst. The rockburst modes and mechanisms under different surrounding rock conditions have been verified by PFC.