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The conventional pressure change method used in leakage tests is sensitive to the ambient temperature variation. We propose a new method using a correlation technique to compensate for temperature variation in pressure change leakage detection. In the proposed method, gas within a vessel is compressed in such a sequence that it shows no correlation with the ambient temperature variation. The extent of leakage is estimated from the correlation between the pressure variation in the vessel and the compression sequence signal. Experimental results showed that leakage can be successfully detected by the proposed method without being affected by temperature variation.

We developed a method of detecting a void under concrete plates using attenuation rate of longitudinal elastic wave in impact-echo test. When a concrete plate contacts with the soil under the plate, a part of energy of longitudinal elastic wave is transmitted into the soil, and the longitudinal elastic wave attenuates rapidly. On the other hand, when a void exists under the plate, a longitudinal elastic wave is reflected completely from the undersurface of plate, and the longitudinal elastic wave attenuates slowly. Then by using the attenuation rates of longitudinal elastic wave, we can distinguish whether a void exists or not under concrete plates. We performed experiments to detect a void under a concrete plate. The surface of the concrete plate with the thickness of 150 mm was impacted by a steel ball with the diameter of 10 mm. The vibration of the surface was measured with Laser Doppler vibrometer. We measured the attenuation rate for the case when the concrete plate contacted with the soil under the plate and the case when a void existed under the plate, respectively. We could distinguish whether a void exists or not by using the attenuation rate.