STRESS-WAVE NONDESTRUCTIVE TESTING OF TUNNELS AND SHAFTS

Case histories of the application of stress-wave methods, such as impact echo, impulse response, and spectral analysis of surface waves, to evaluate conditions of concrete-lined tunnels and shafts are presented. These nondestructive evaluation methods provide data on the concrete integrity, the contact condition at the interface between concrete and rock or soil, and the stiffness (velocity, elastic modulus, or both) profile. Conditions such as fractures, void, and comparatively weak materials can all be identified from the test surface without drilling coreholes into the materials. A brief technical description of each nondestructive evaluation method is included along with the respective case history data. In addition, the potential for rapid, near-continuous testing using innovative stress-wave measurement instrumentation with PC-based data acquisition and analysis is discussed.