Geophysical and geotechnical assessment of a railway embankment failure

Abstract

A geophysical investigation was carried out after the failure of an important railway embankment in the south-east of Ireland. The embankment, which had a long-term history of stability problems, was studied using a combination of ground-penetrating radar (GPR), electrical resistivity tomography (ERT), multichannel analysis of surface waves (MASW) and geotechnical testing. A significant thickening of the ballast layer around the failure location was observed using GPR, which confirmed the existence of an ongoing stability problem in the area. ERT profiles determined the presence and spatial extent of a significant layer of soft clay both beneath and to the east of the embankment, which could have a major impact on its long-term stability. ERT also detected steeply sloping bedrock close to the failure zone that is likely to have contributed to the long-term settlement of the embankment, which necessitated frequent re-ballasting. MASW confirmed the presence of the steeply sloping bedrock in addition to determining the low stiffness (G max ) values of the embankment fill.High quality sampling of the soft clay deposit was undertaken and strength and compressibility tests revealed the importance of this layer to both the on-going serviceability problems evident for the original embankment and the stability problems encountered by the remodelled section.

Landslide investigations in the northwest section of the lesser Khingan range in China using combined HDR and GPR methods

“…It is one of the standard methods of geophysical prospecting for investigating shallow geological problems (Cardarelli et al 2003;Yamakawa et al 2010;Donohue et al 2011;Sauvin et al 2014). Current applications of HDR focus on landslide recognition and permafrost detection, while investigations on debris thickness in arctic and alpine environments are comparatively sparse (Carpentier et al 2012;Donohue et al 2011;Perrone et al 2014).…”

“…It is one of the standard methods of geophysical prospecting for investigating shallow geological problems (Cardarelli et al 2003;Yamakawa et al 2010;Donohue et al 2011;Sauvin et al 2014). Current applications of HDR focus on landslide recognition and permafrost detection, while investigations on debris thickness in arctic and alpine environments are comparatively sparse (Carpentier et al 2012;Donohue et al 2011;Perrone et al 2014). GPR is based on the measure of reflection of radar waves in the subsoil, and is largely focused on the fields of natural resource exploration, hydrogeology, engineering and archaeological investigation (Sass 2007;Sass et al 2008;Schrott and Sass 2008;Zajc et al 2014).…”

Aged embankment imaging and assessment using surface waves

“…They can inform further SI design in relation to poor ground conditions and aid location of more challenging invasive methods such as pitting, cone penetration resistance testing and coring (Gunn et al, 2012;Raines et al, 2011). Rayleigh wave analysis, in particular, has been established as a reliable tool for the characterisation of the small strain stiffness (shear modulus G) of the near surface at the engineering scale (Donohue et al, 2011(Donohue et al, , 2013aFoti, 2003). Rayleigh waves are dispersive; their phase velocity varies with wavelength and, hence, depth of investigation (Socco and Strobbia, 2004).…”

“…Surface wave surveys can be mobilised to image the volumetric distribution of shear wave velocity and, thus, map the small strain stiffness (shear modulus) throughout earthworks, from which heterogeneity can be assessed (Bergamo et al, 2016;Donohue et al, 2011;Gunn et al, 2013Gunn et al, , 2015bZagyapan and Fairfield, 2000). These images can be used to assess the unique internal heterogeneity-and strength-related characteristics arising from the original tipping construction methods, or due to subgrade problems resulting from progressive deterioration.…”

Assessment of soil compaction properties based on surface wave techniques

“…These applications include assessment of liquefaction potential [3], geotechnical verification of compaction [2,4,6], and site characterization [5]. These nondestructive methods have been proved to be efficient compared to the conventional invasive mechanical techniques where the shear wave velocity (V S ) is theoretically related to the shear modulus, G max as shown in the Equation 1 below:…”