Experimental Study On Mechanical Properties Of Microfissured Rhyolite Under Triaxial Test

During the construction of tunnel and slope, the failure of surrounding rock and slope is often occurred due to excavation and unloading. Especially in the deep, high ground stress and brittle rock tunnels, it will often lead to rockburst, and it is dangerous to workers. Corresponding work have been carried out based on the columnar joint rhyolite from Daxiangling Niba mountain tunnel zone. Firstly, statistic the microfissure morphological of specimens through sketching, then series of conventional triaxial tests and triaxial confining pressure reduction tests are carried out with the MTS815rock mechanic test system, in order to obtain the different stress-strain caves under different microfissure morphological specimens and stress patch. The strength and deformation properties of microfissure rock are obtained and the impact law of initial microfissure on the fracture mechanism and mechanical properties are analyzed. Finally, the mechanical property of rhyolite are studied with fracture mechanics and damage mechanics.The tests show that:(1) Under the conventional triaxial tests, the rhyolite specimens are obviously brittle and their initial microfissure propagate to macro shear plane with the inclination between-21°to23°; slip rupture plane is appeared in some specimens which exist initial weak plane;(2) the mechanical properties of triaxial tests are greatly impacted by the initial advantage angle. The mechanical properties of the specimens which exist the obvious initial advantage angle or its initial advantage angle is close to the potential shear fracture angle are worse. When the initial advantage angles of microfissure parallel or perpendicular to the maximum principle stress, and their mechanical properties are better;(3) to compare with conventional triaxial tests, it is more prone to form splitting cracks and its mechanical properties are worse under triaxial confining pressure reduction tests. Especially, when the specimens of triaxial confining pressure reduction tests have been preloaded with uniaxial tests, their mechanical properties are the worst and they are the most brittle;(4) To the preloading specimens, their strength, elastic modulus and deformation modulus are higher, but Poisson’s ratio remains the same under conventional triaxial tests; on the contrary, their mechanical properties are the worst under triaxial confining pressure reduction tests.The theoretical analysis shows that the worst angle is (45°-(?)/2), which consistents with the experimental results. Finally, consider the damage of rhyolite according with exponential distribution and existing initial damage, combined elastic damage mechanics, obtain the constitutive model of microfissured rhyolite. The experimental results and theoretical analysis can provide meaningful reference to the stability studies of microfissured tunnel surrounding rock.