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Abstract First of all，the transmission coefficient and the reflection coefficient of P wave crossing a elastic joint are deduced based on the theories both of elastic waves and displacement discontinuity. According to the stress wave time delay theory，the analytical solution of phase delay and group delay are given when the joint obeys the elastic Hooke?s theory. A universal distinct element code(UDEC) is used to simulate stress waves propagation in rocks with a single joint and five parallel joints，respectively. And the incidence stress wave is cosine Gauss pulse. All of the main research results can be summarized as follows. (1) When P wave transmitting the rock model with only a single joint，the phase delay is consistent with the analytical solution calculating from the unfiltered waves，while the group delay deviates from the analytical solution. After the 97–103 Hz band-pass filtered，the phase delay and group delay are both consistent with the analytical solution. (2) For the rock models with multiparallel joints，when the distance of these joints is larger than one half of the wave length of the cosine Gauss pulse，the group delay from filtered wave is more or less in line with the analytical solution. However，if the distance of these joints is smaller than one half of the wave length，the phase delay and group delay both deviate from the analytical solution. (3) As we all know，the wave-front is never disturbed by the multiple reflection. The wave-front delays of three multiparallel joints models are in line with each other under different joint stiffnesses，and the difference between these delays and the analytical results is limited. Under the assumption that the joint is a liner elastic model，the results of this research can be used to predict the joint stiffness or number of joints in rock masses.
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Received: 06 August 2012
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2013, Vol. 32 
