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Abstract A series of conventional triaxial tests with uniaxial preloading and triaxial tests with the confining pressure reducing were carried out on rhyolite specimens with natural micro fissures as the base of research on tardy failure of fissured surrounding rock of tunnel under the disturbance of excavation. Stress-strain curves of specimens with different micro fissures on two kinds of stress paths were obtained. The natural rhyolite specimens with micro fissures were found all to be remarkable brittle without a conspicuous yielding phase. The characteristics and distribution direction of micro fissures greatly affected the mechanical properties of specimens under two different stress paths. The micro fissures perpendicular to the maximum principal stress were difficult to extend leading to shear destruction and better mechanical behaviour. While if the initial dominating angle was small and the micro fissures linked dendritically with each other，macro tensile cracks would be formed in specimens，which weaken the mechanical behaviour of rocks. When the initial dominating angle of specimens with natural micro fissures was 46°in conventional triaxial tests，the mechanical properties were the worst. The lateral micro fissures were closed under uniaxial preloading. The strength，the elastic modulus and the deformation modulus of specimens measured with the conventional triaxial tests under pre-loading were increased due to the closing of fissures，Poisson?s ratios were basically unchanged and the characteristic of brittleness was more conspicuous.
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Received: 25 September 2013
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2014, Vol. 33 
