Detection of Cavities Beneath Concrete Structures Using Acoustic Wave in Dry and Saturated Soils

The objective of this study is to detect cavities beneath underground structures in dry and saturated soils using acoustic waves. A trench is excavated in dry soil, and a concrete plate is placed on the trench to simulate a cavity beneath the underground structure. A cavity below the groundwater level is simulated by watering the cavity and soil. The acoustic waves are measured using a condenser microphone, and the flexibilities of the measured acoustic waves are calculated. The test results show that the flexibility increases at the cavity section due to the flexural vibration of the concrete plate. Moreover, the difference in flexibility between the cavity-free and cavity sections is greater for air-filled cavity than water-filled cavity. This study reveals that microphones may be effectively used for detection of cavities beneath underground structures in dry and saturated soils.