Natural rocks often contain a large number of microfissures that have great effect on the deformation, strength and failure mechanism of rocks. The engineering construction will change the stress magnitude and stress state, thus causing microfissure to propagate until a macroscopic failure plane is formed. In order to study the strength properties of such microfissure rocks, and provide basic data for investigating the water inflow and mud burst mechanism of tunnel excavated in microfissure-well-developed rocks, a series of triaxial compression tests under different loading path are carried out on rock specimens drilled from rhyolite blocks taken from the site of Daxiangling Niba mountain tunnel. The strength and deformation properties of microfissure rock are obtained; the influences of factors such as the initial angle of the microfissure and morphology on the strength and deformation-failure of microfissure rock are analyzed.
The nature rock often contains a large number of microfissures internal, which due to the complex geological environment in the process of formation and deposition. It reflects not only in the consolidation stage of stress-strain curve, but also in the difference of its deformation and mechanical characteristics. With the advance of Great Western Development in china and the implementation of high standard and largescale infrastructure, a large number of deep and long tunnels will be constructed, such as the length of water tunnel in Jinping-II Hydropower Dam is about 17 km. Because of the high ground stress, rock in the tunnel site contains a large number of microfissure, they would further extend and form new cracks with construction, thus change the mechanical characteristics of protolith and bring great difficulties to the design and construction of these key projects.
To the experimental study of the mechanical properties of the microfissure rock, because of the random microfissure of nature rock, most scholars carried out a series of uniaxial, biaxial, triaxial tests and numerical simulation through pre-existing fissure rocklike material, then analysis the cracking mode of the cracks and the effects of fractured angle and density on fracture morphology and mechanical properties (Bobet A, et al. 1988; Huang, et al. 2007; Horii, et al. 1985; S. Nemat-Nasser, et al. 1984). Also some scholars have made related research with nature microfissure rockswhich are granite and marble (Chunli, et al. 1993, 1998; Kou, et al. 1987;You, et al. 2008). However, due to the complexity of the nature microfissure rock test, the result of mechanical research is rare relatively. To some extent, it restricts the development of the design and construction of deep and long tunnel and disaster prevention and reduction.
