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Abstract In order to study the effect of water-saturated state on mechanical properties of rock in coal measure strata，Brazilian Split test，uniaxial and pseudo-triaxial compression experiments are carried out to investigate sandstone，sandy mudstone and mudstone specimens under natural and water-saturated state by rock mechanics test equipment RMT–150B. The results are as follows：the average rate of water absorption of sandstone，sandy mudstone and mudstone is between 0.241% and 0.482%；water absorption rate with respect to time can be fitted with logarithmic relationship. Different influences of the strength and deformational character among these three types of rocks are found after reaching water-saturated state，mudstone performs most obviously，then comes the sandy mudstone and the sandstone. The softening coefficient of tensile strength is roughly between 0.40 and 0.92；softening coefficient of uniaxial compression strength is between 0.58 and 0.94；reducing coefficient of elastic modulus is between 0.58 and 0.95；reducing coefficient of deformational modulus is between 0.68 and 0.94；and the reducing coefficient of Poisson ratio locates in the range of 1.08–1.11. The softening coefficient of peak strength measured by triaxial compression tests-K and the confining pressure-?3 are approximately positive correlated. It is indicated that the sensitivity of peak strength to the confining pressure in water-saturated state is greater than that in natural state. Water-saturated state can reduce the cohesion of these rock specimens；the percentage of reducing lies between 20.6 % and 67.0%. On the other hand，internal friction coefficient almost keeps in the same level；it is shown that the former coefficient is a structural parameter and the latter is a material parameter.
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Received: 22 December 2010
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2011, Vol. 30 
