MASW tests were performed on 11 sections of the Navigli channel to assess the relative condition of the sidewall. The minimum and maximum group shear wave velocities were Vs=667 m/s and VR=1200 m/s whereas the minimum and maximum shear wave phase velocities were Vph= 500 m/s and Vph=1140 m/s. The frequency with higher energy varied from 500 Hz to 1600 Hz; thus the penetration of surface waves was enough to reach the back surface of the sidewall (approximately at 1m from the surface of the wall).
A fuzzy model is developed to compute a condition index as a function of the group velocity, the maximum and minimum phase velocities, the frequency with higher energy in the Fourier spectrum, and the attenuation coefficient of each section. The condition index shows that Sections 1L, 6R, 8R, 9L, 10R, 10L, 11R and 11L are the weaker or less stiff sections of the sidewall. Visual inspection of these sections revealed that surface conditions are fine for most of them. However, voids and cracks are evident near the array of transducers. In addition, low velocity and high attenuation could be the result of more severe defects such as internal fractures and weaker conditions of the brick and mortar that could not be evident on the surface.
The authors express their gratitude to the regional and civic administrations of the city of Milan, Italy, and the technicians of the Laboratory of the Politecnico di Milan, Structural Engineering Department for their assistance. Special thanks to Andrea Bonizzi, who helped in the data collection and preparation of figures. This research is part of a study on nondestructive testing of geomaterials that is partially supported by the Earth and Environment Technology (ETech) of the Ontario Center of Excellence, the Natural Sciences and Engineering Research Council of Canada (NSERC), and the National Research Council Canada (NRC). Their support for this project is very much appreciated.
Table 1. Field data and calculated condition index (CI)
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