Conclusions

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.

Acknowledgements

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)

Section

Vr

m/s

Vph1

m/s

Vph2

m/s

f1

Hz

a

Condition

Index

Condition

State

1R

N/A

N/A

N/A

N/A

N/A

N/A

N/A

1L

754

800

600

700

0.55

0.917

Damaged

2R

1040

800

600

800

0.20

0.000

Very Good

2L

870

870

540

588

0.25

0.582

Moderate

3R

1000

1140

850

550

0.45

0.500

Moderate

3L

1030

880

700

1000

0.30

0.250

Good

4R

950

625

400

910

0.42

0.429

Moderate

4L

930

1000

600

900

0.23

0.250

Good

5R

930

730

430

1150

0.33

0.437

Moderate

5L

930

930

600

1100

0.33

0.311

Good

6R

767

750

600

650

0.56

0.917

Damaged

6L

1200

1000

600

1600

0.34

0.155

Good

7R

820

870

790

900

0.26

0.424

Moderate

7L

770

810

720

810

0.28

0.500

Moderate

8R

787

800

700

850

0.38

0.625

Deteriorated

8L

880

836

766

1150

0.40

0.465

Moderate

9R

837

800

600

1016

0.34

0.478

Moderate

9L

910

700

300

650

0.34

0.558

Moderate

10R

783

500

400

500

0.38

0.750

Deteriorated

10L

837

500

400

500

0.38

0.652

Deteriorated

11R

667

580

400

650

0.65

0.917

Damaged

11L

745

745

500

660

0.20

0.750

Deteriorated

Average

878

802

601

840

0.36

0.500

Moderate

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