Aged embankment imaging and assessment using surface waves

Abstract

Rapid, non-intrusive surface wave surveys provide depth profiles from which ground models can be generated for use in earthwork condition assessment. Stiffness throughout earthworks controls the behaviour under static and dynamic loads, and characterising heterogeneity is of interest in relation to the stability of engineered backfill and life-cycle deterioration in aged utility and transportation infrastructure. Continuous surface wave methods were used to identify interfaces between fine-and coarse-grained fill in an end-tipped embankment along the Great Central Railway in Nottinghamshire, UK. Multichannel analysis of surface wave (MASW) methods were used to characterise subsurface voiding in a canal embankment along the Knottingley and Goole canal near Eggborough, Yorkshire. MASW methods are currently being used to study extreme weather impacts on the stability of a highplasticity clay embankment along the Gloucestershire-Warwickshire railway near Laverton. Optimal results were obtained using equipment capable of generating and detecting over wide frequency ranges. Notation

Surface wave surveys for imaging ground property changes due to a leaking water pipe

“…These are observed as the ground surface roll that radiates from the vertical impact and are utilised in surface wave surveys. The shear wave velocity is approximately 1.1 times the Rayleigh wave velocity and is controlled by the small strain stiffness and density of the soil (Richart et al, 1970;Gunn et al, 2016). Rayleigh waves propagate with a reverse-ellipsoid particle motion within different depth intervals in the ground shown in Fig.…”

“…A depth equivalent to one third the wavelength is most commonly used because a significant proportion of the particle motion in the ground associated with Rayleigh wave propagation is approximately at this depth (Gunn et al, 2006a(Gunn et al, , 2006bJoh, 1996;Richart et al, 1970). Vertical 2D sections were constructed along each array by contour infilling using anisotropic inverse distance weighting over a grid between each of the 7 shear wave velocity-depth profiles collected along each geophone array (Gunn et al, 2016). Equivalent small strain stiffness logs and sections can also be estimated using the product of the square of the shear wave velocity and the bulk density, where for example, the bulk density can be estimated from the profile sampling using simple density rings.…”

“…Time-lapse electrical resistivity tomography has successfully captured complex structures and groundwater movements driving deterioration, even in heterogeneous environments, with a subsurface resolution significantly closer to the true in situ heterogeneity than achieved using conventional intrusive or point sensing (Chambers et al, 2007(Chambers et al, , 2013(Chambers et al, , 2014Gunn et al, 2015a). Surface wave surveys provide a reliable means of non-invasively imaging the shear wave velocity and associated stiffness distributions within engineered structures (Gunn et al, 2006a(Gunn et al, , 2006bGunn et al, 2016;Bergamo et al, 2016). Electrical and seismic imaging applications have been successfully adapted for use at increasing scales, e.g.…”

“…It is for this reason that the soil profile exhibits an increasing shear wave velocity with depth, and because different Rayleigh wave frequencies propagate in different soil depth intervals, the phase velocity is dispersive. Shear (and Rayleigh) wave velocity is not directly dependent upon shear strength, but because of these associations, it is seen as a non-invasive, qualitative proxy for assessing shear strength changes, especially in disturbed, landslipped ground and earthworks (Gunn et al, 2016;Uhlemann et al, 2016). In coarse grained soils, such as sand and gravel, the stiffness, shear strength and shear wave velocity are dependent upon the packing density of the soil grains, and are largely insensitive to saturation.…”

Editorial

“…Warren and her co-workers utilised thermal imaging technology to assess condition and possible defects of drystone walls (Warren et al, 2016). Gunn et al (2016) adapted the surface wave image profiling method to evaluate the condition and integrity of embankments. Both proposed inspection technologies are approved to be promising and reliable for evaluating the condition of targeted structures.…”