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| STUDY OF MECHANICAL CHARACTERISTICS OF LIMESTONE
UNDER UNLOADING CONDITION |
| ZHAO Guobin1，ZHOU Jianjun2，WANG Sijing1 |
| (1. Key laboratory of Engineering Geomechanics，Institute of Geology and Geophysics，Chinese Academy of Sciences，Beijing 100029，China；2. State Key Laboratory of Shield Machine and Boring Technology，China Railway Tunnel Group Co.，Ltd.，Zhengzhou，Henan 450001，China) |
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Abstract Under unloading condition，the mechanical characteristic of rock sample is notably different from that under loading condition. Because of constructing of tunnel，loading and unloading experiments are carried out to study the unloading mechanical characteristics of –3 limestone. After analyzing test data，some conclusions are drawn：(1) The lateral deformation and volume dilatancy of rock sample along unloading direction are the dominant failure characteristics. (2) Brittle characteristic of rock is more notable than that under loading condition for this rocks，especially after peak strength. So rockburst may take place when underground engineerings are constructed. (3) Under unloading condition，compressive strength is less than that under loading condition. As far as this rock is concerned，the peak strength is reduced by 25.65% and residual strength by 73.15%. (4) For shear strength，peak strength and residual strength of cohesion both decrease and those of inner friction angle increase. (5) Under two kinds of testing conditions，deformation modulus E50 and Poisson?s ratio are related with confining pressure. The different is that deformation modulus decreases firstly and when confining pressure reaches to some value，deformation modulus begins to increase. Then for poisson?s ratio，the trend of changing is opposite to deformation modulus.
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Received: 09 March 2012
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2013, Vol. 32 
