Spectral analysis of surface wave response of multi-layer thin cement mortar slab structures with finite thickness

Abstract

The method of spectral analysis of surface waves (SASW), a nondestructive testing method, has mainly been developed and used for many years in the fields of geotechnical engineering and highway engineering, such as for examining the material properties of pavement systems and soil media under an infinite half-space condition. Extensive research in this area has been focused on understanding the applicability and limitations of the SASW method in recent decades. This method consists of generation, measurement, and processing of dispersive surface waves. During an SASW test, the surface of the medium under investigation is subject to an impact to generate surface wave energy at various frequencies. Two vertical accelerometer receivers are set up near the impact source to detect the energy transmitted through the testing media. By recording signals in digitized form using a data acquisition system and processing them, surface wave velocities can be obtained by constructing a dispersion curve. Through forward modeling, the shear wave velocities can also be found, which can be related to various material properties. This paper presents the relationship between the theoretical and experimental compact dispersion curves when the SASW method is applied to multi-layer thin cement mortar slab systems with a finite thickness. The test results of surface wave velocity obtained from the experimental compact dispersion curve are found to have higher values than the results obtained from the theoretical dispersion curve due to different boundary conditions and reflections from the boundaries. An experimental study was conducted to examine if the dispersive characteristics of a Rayleigh wave exist in the multi-layer cement mortar slab systems. This study can be utilized in examining structural elements of general concrete structures and can be applied in the integrity analysis of concrete structures with a finite thickness.