Experimental investigations on the short- and long-term behaviour of Jinping marble in deep tunnels

Abstract

The tunnels of Jinping II hydropower station are characterised by its ultra-long and deep-buried properties. For the stability of the tunnels, it is of great important to investigate the short-term and time-dependent mechanical behaviour of surrounding rocks. The triaxial compression tests with confining stress up to 100 MPa were performed in order to complete the short-term mechanical behaviour of Jinping marble. Typical characteristics of brittle rock, such as volumetric compaction–dilatancy transition, degradation of elastic modulus, dependence of strength and failure mode on confining stress were observed. Two constant axial stresses were applied in the uniaxial compressive creep tests, and tertiary creep phases were realised. The evolutions of creep strain of the uniaxial compressive creep tests presented obvious anisotropy. One triaxial compressive creep test was also performed under confining stress of 10 MPa. The creep strain rates in both axial and lateral directions of triaxial compressive creep tests were significantly lower than those of uniaxial compressive creep tests. The significant anisotropy of creep strain in uniaxial compressive creep tests was attenuated in triaxial compressive creep tests. Immediate support is thus of great important to provide an effect as confining stress after the excavation of the tunnel under high in situ stress.