1. Vibroacoustics Academics: Jen Muggleton, Emiliano Rustighi Researchers: Michal Kalkowski, Michele Iodice

2. Aim To develop novel vibro-acoustic methodologies to assess the condition of the buried utility service, geotechnical and transport infrastructures

3. Objectives To use a pipe vibration method to assess the condition of buried pipework To investigate a variety of ground excitation methods to interrogate both the ground and the buried infrastructure To explore a tree excitation method to determine the location of tree roots in order to identify areas of pipe network at risk of damage To develop vibro-acoustic methods to measure relevant wavespeeds (including variation with depth) in situ

4. Pipe Excitation Method: Background In MTU, pipe excitation technique developed When pipe is excited, wave propagation in the pipe mirrored at the ground surface and the run of the pipe can be determined from ground vibration contours In addition, bends and holes in the pipe wall may be detected as well as changes in soil condition

5. Example Pipe Discontinuities pipe end 32mm hole bend in pipe

6. Example Soil Discontinuities changes in soil type

7. Development of theoretical models Prediction of pipe wavenumbers (wavespeed and attenuation) for different soil coupling conditions

8. Development of theoretical models Prediction of ground surface response arising from wave motion in pipe

9. Torsional Motion Torsional motion may be linked to certain types of pipe failure, in particular spiral fracture of cast iron pipes Ultrasonic inspection techniques frequently exploit torsional waves but little is known about their behaviour at audio frequencies Modelling work has been undertaken to predict dispersion characteristics (wavespeed & attenuation) for buried cast iron/plastic pipes ground surface response as a result of torsional wave motion in pipe The individual terms contributing to the wavenumber expression can be readily identified as: the in-vacuo torsional wavenumber, k T ; a pipe wall mass component, ω 2 ρ p h; a soil shear stiffness component, μ m /a; and a shear wave radiation component associated with the Hankel function ratio,

10. Next Steps T o investigate effects of pipe discontinuities on wave propagation – In pipe – At ground surface To undertake experiments on test sites to – Locate pipe defects – Detect areas of flooded ground

11. Ground excitation methods: Background Point Vibration Technique Applicable when no direct access to the pipe is available At low frequencies, ground exhibits classic mass-spring behaviour with a well-defined resonance Changes in resonance frequency can be used to detect the presence of a buried object close to the surface Vertical excitation is applied at the ground surface at several points along a line and accelerance (acceleration/force) is measured at each point Potentially extremely quick to implement Has been used successfully to detect a number of shallow-buried services

12. Ground excitation methods: Background Shear wave Technique Applicable when no direct access to the pipe is available Directional shear waves generated at ground surface using exciter attached to rake (excitation direction is perpendicular to measurement line) Line of geophones used to measure ground surface vibration Generalized cross correlation functions used to extract time delay information Time domain stacking technique employed to generate cross- sectional images of the ground Method has been successful at detecting both plastic and metal water pipes and empty metal pipes shaker with rake attachment geophones approximate run of pipe

13. Current Work Signal processing enhancements – Various signal processing enhancements have been investigated including data apodization data enveloping – The robustness of the algorithms to errors in wavespeed estimation has also been considered Use of surface waves to detect road surface cracks – Using wave decomposition – Exploiting MASW/MISW differences

14. Next Steps Measurements on test site(s) Comparison of point vibration technique with falling weight deflectometer Experimental measurements on road surface delamination with point vibration technique

15. Tree excitation: Background Tree roots well known to be disruptive to underground pipe and cable networks Damage can occur due to a number of different mechanisms, e.g. via direct penetration of the pipework, resulting in leakage through alterations in the ground water content locally by means of a gradual displacing of the pipework from its original location, resulting in pipe fracture Detecting extent of root development of individual trees from ground surface could identify areas of infrastructure at risk

16. Field measurements Measurements on real trees demonstrate that energy can effectively be transmitted from the trunk into the root system and thence the ground

17. Modelling & laboratory measurements Root radius variation along the length is often close to exponential Wave propagation in exponentially tapered rods studied, to understand the phenomena expected in real tree roots A purpose built root model was used in lab experiments to estimate the wavenumbers for longitudinal and flexural waves from equidistant FRF measurements

18. Next steps The rod will now be buried in a sandbox allowing for an investigation of the soil effect on wave propagation

19. Interrogation of the soil Comparison of soil excitation methods to excite different wavetypes Combining vertical & horizontal ground vibration responses to extract the Rayleigh surface wave information Comparison of geotechnical/geophysical properties derived using seismic and electromagnetic methods Use of inversion methods to extract near-surface wavespeed information in both – homogenous soil – a layered soil

20. Summary Significant progress made in all four areas and all show considerable promise – Pipe vibration – Ground vibration – Tree excitation – Soil interrogation Next steps – Continue developing our fundamental understanding via Analytical & numerical modelling Laboratory & field experiments – Testing on real sites

21. And finally.…. Thankyou & Merry Christmas !