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Trafford, Andrew
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Trafford, Andrew
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Trafford, Andrew
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Now showing 1 - 5 of 5
- PublicationThe Application of Distributed Acoustic Sensing for Shallow Marine Investigations – an Intertidal Case Study(European Association of Geoscientists & Engineers, 2021-09-02)
; ; ; ; Typically, there is a paucity of geotechnical information available to designers of offshore foundations for marine renewable structures, which often results in highly conservative designs. Recent innovations offshore (e.g. McGrath et al. 2016; Long et al. 2020)) seismic surface wave (SW) measurements have highlighted their potential for providing offshore geotechnical information, thereby reducing design uncertainty. There is also an increasing recognition of the value of these measurements from the geotechnical industry, with Lunne (2013) recommending that measurements of seismic shear wave velocities (Vs) should be standard practice for important offshore site investigations. Vs is related to the small strain shear modulus Gmax, which is a critical input parameter for several applications, including static and dynamic analysis of foundation systems, soil liquefaction analysis and input for advanced constitutive soil models. The main disadvantage of current offshore SW practice is a relatively slow data acquisition procedure, which, in turn reduces the spatial coverage of the approach.366Scopus© Citations 2 - PublicationDistributed acoustic sensing for active offshore shear wave profiling(Springer, 2022-06-11)
; ; ; ; ; The long-term sustainability of the offshore wind industry requires the development of appropriate investigative methods to enable less conservative and more cost-effective geotechnical engineering design. Here we describe the novel use of distributed acoustic sensing (DAS) as part of an integrated approach for the geophysical and geotechnical assessment of the shallow subsurface for offshore construction. DAS was used to acquire active Scholte-wave seismic data at several locations in the vicinity of a planned windfarm development near Dundalk Bay, Irish Sea. Complimentary additional datasets include high-resolution sparker seismic reflection, cone penetration test (CPT) data and gravity coring. In terms of fibre optic cable selection, a CST armoured cable provided a reasonable compromise between performance and reliability in the offshore environment. Also, when used as a seismic source, a gravity corer enabled the fundamental mode Scholte-wave to be better resolved than an airgun, and may be more suitable in environmentally sensitive areas. Overall, the DAS approach was found to be effective at rapidly determining shear wave velocity profiles in areas of differing geological context, with metre scale spatial sampling, over multi-kilometre scale distances. The application of this approach has the potential to considerably reduce design uncertainty and ultimately reduce levelised costs of offshore wind power generation.Scopus© Citations 10 23 - PublicationTime-Lapse Monitoring of Moisture Induced Landslide Using Surface Waves at Hollin Hill Landslide Obsevatory(European Association of Geoscientists & Engineers, 2021-09-01)
; ; ; ; ; For about fifteen years, the Hollin Hill site has been used as a landslide research site to test different geophysical characterization and monitoring methods, to assess temporal and spatial stability, and the following methods are regularly evaluated on site: ERT resistivity mapping (Chambers et al. 2010, Uhlemann et al. 2017), self-potential methods SP (Chambers et al. 2008), more recently seismic refraction tomography SRT (Whiteley et al. 2020, Uhlemann et al. 2016). The dynamics and ongoing subsurface processes of the Hollin Hill landslide are therefore relatively well described in literature (Whiteley at al. 2019a). Seismic methods based on characterization of P-wave (Vp) and S-waves (Vs) propagation and in particular on Vp /Vs ratio are commonly used in a landslide context (Grandjean et al. 2009, Mainsant et al. 2012). Since mid-2000, methodological improvements have led to increased routine use of dispersion inversion of Vs in hydrological applications (Pasquet et al. 2015; Dangeard et al. 2016) and in geotechnical applications (Donohue et al. 2011, Bergamo et al. 2016). This abstract therefore discusses current geophysical research to monitor seasonal variations using surface waves content (Rayleigh waves) from SRT acquisitions, in the context of moisture induced landslide monitoring, at the Hollin Hill Landslide Observatory.305 - PublicationDistributed Acoustic Sensing for the Geotechnical Assessment of Offshore Renewable Developments(European Association of Geoscientists & Engineers, 2023-09)
; ; This paper discusses a recent technological addition to the field of offshore geotechnical investigation. Distributed Acoustic Sensing (DAS) utilises fibre optic cables as continuous sensing elements, measuring small strain imposed on the glass core by the transmission of acoustic energy along the sea bed / water interface ( Trafford et al. 2021 , Trafford et al. 2022a ). The potential benefits of this over traditional sediment profiling methods is the rapid data acquisition over large scale arrays. As well as providing detailed information for the design of offshore foundations the potential to deploy extensive linear arrays make the proposed methodology ideal for the assessment of linear investigations such as transmission cable route options.12Scopus© Citations 1 - PublicationDistributed acoustic sensing for seismic surface wave data acquisition in an intertidal environment(Society of Exploration Geophysicists, 2024-07)
; ; ; ; The application of distributed acoustic sensing (DAS) for shallow marine seismic investigations is assessed, in particular with respect to the collection of seismic surface wave data in an intertidal setting. Appropriate selection and directional sensitivity of fiber-optic cables is considered and the measured data is validated with respect to conventional seismic data acquisition approaches, using geophones and hydrophones, along with independent borehole and seismic cone penetration test (SCPT) data. In terms of cable selection, a reduction in amplitude and frequency response of an armored cable is observed, when compared with an unarmored cable. For seismic surface wave surveys in an offshore environment where the cable would need to withstand significant stresses, the use of the armored variant with limited loss in frequency response may be acceptable from a practical perspective. The DAS approach also has indicated good consistency with conventional means of surface wave data acquisition, and the inverted VS also is very consistent with downhole SCPT data. Observed differences in phase velocity between high tide (Scholte wave propagation) and low tide (Rayleigh wave propagation) are not thought to be related to the particular type of interface wave due to shallow water depth. These differences are more likely to be related to the development of capillary forces in the partially saturated granular medium at low tide. Overall, this study demonstrates that our novel approach of DAS using seabed fiber-optic cables in the intertidal environment is capable of rapidly providing near-surface S-wave velocity data across considerable spatial scales (multikilometer) at high resolution, which is beneficial for the design of subsea cables routes and landfall locations. The associated reduction in deployment and survey duration, when compared with conventional approaches, is particularly important when working in the marine environment due to potentially short weather windows and expensive downtime.10