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Smart Structures and Systems
  Volume 28, Number 4, October 2021 , pages 567-578

A hybrid nondestructive testing method for detecting cavities behind the retaining wall
Jung-Doung Yu, Jong-Sub Lee and Hyun-Ki Kim

    This study proposes a combination of nondestructive testing methods for detecting soil cavities behind retaining walls, which adversely affect the stability of the sloping ground or retaining structures. An experimental study is conducted using a soil chamber filled with dry sands retained by a concrete wall plate. A hemispherical soil cavity is simulated just behind the wall plate, and elastic wave reflections of impacts on the wall are measured using accelerometers. The measured elastic waves are analyzed using the signal energy in time domain and predominant frequency and mobility spectrum in frequency domain. In addition, spatiotemporal changes in the surface of the wall during heating and cooling sequences are monitored using infrared thermography. The captured thermal image is then used for identifying the cavity. Experimental results show that the cavity leads to increases in the signal energy, predominant frequency, and flexibility in the mobility spectrum. The contrasts in the thermal images effectively reveal the shapes and locations of the soil cavity. This study demonstrates that the hybrid testing method that conducts a careful inspection by elastic waves on areas suspected in the preliminary scanning by the infrared thermography can be competitive and effective for detecting soil cavities.
Key Words
    cavity detection; elastic wave; nondestructive evaluation; retaining wall; thermal image
(1) Jung-Doung Yu, Jong-Sub Lee:
School of Civil, Environmental, and Architectural Engineering, Korea University, 145 Anam-ro, Seongbuk-gu, Seoul 02841, Republic of Korea;
(2) Hyun-Ki Kim:
Department of Civil and Environmental Engineering, Kookmin University, 77 Jeongneung-ro, Seongbuk-gu, Seoul 02707, Republic of Korea.

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