Effects of open joints and weak layers on wave propagation in geologic materials

Computations involving stress wave propagation in rocks containing a weak layer in a strong rock and in rocks with open joints are presented. These computations were based on laboratory experiments using specimens fabricated from Indiana limestone and grout. The results indicate that the weak layer significantly attenuated the amplitude of the stress wave as it propagated through the layer, but the pulse width remained nearly constant. For the open joint case the amplitude remained constant as the width increased until at a sufficiently large separation the amplitude was attenuated. The pulse width, however, decreased with an increasing joint separation. The wave structure may lead to a determination of the quality of the rock through which a stress wave has traveled, i.e., open joints, weak layers, or intact rock.