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Multichannel analysis of surface waves (MASW) for offshore geotechnical investigations
Abstract Multichannel analysis of surface wave (MASW) surveys are commonly used onshore to produce shear wave velocity (Vs) profiles. This paper describes its use in offshore geotechnical investigations (underwater MASW - UMASW) where the focus was on the upper 15 m of the sediment profile to aid the design of structures such as marine pipelines, cable routes and shallow anchor systems. UMASW was shown to provide reliable data in Irish offshore conditions in water depths of up to 50 m. The receiver spacing and array length, rather than the characteristics of the air gun seismic energy source, were the primary control on signal penetration and resolution of individual sediment layers. Good resolution of the properties of the upper 5 m of sediment was found by reducing the receiver spacing to as low as 0.3 m. A test site, with a broad intertidal zone, allowed coincident land, marine and direct measurements to be compared and Vs profiles obtained from UMASW, onshore MASW and by seismic cone testing (SCPTU) were in good agreement. Vs profiles estimated from published correlations with CPTU data in sandy sediments agreed well with the measured values. Inversion of data using different software packages showed only a minor variation in results.
Highlights Focus of work on top 15 m of offshore sediment. Obtained good data in harsh conditions to water depth of 50 m offshore western Ireland. Showed receiver spacing much more important than seismic source in resolving Vs in near bed offshore sediments. Showed good agreement in Vs profiles obtained from offshore UMASW, onshore MASW and by seismic cone testing (SCPTU). Any relatively low volume air gun source (12 in3 or similar) contains sufficient bandwidth for use in environments similar to those described here. Obtained very similar Vs profiles with two different inversion software codes.
Multichannel analysis of surface waves (MASW) for offshore geotechnical investigations
Abstract Multichannel analysis of surface wave (MASW) surveys are commonly used onshore to produce shear wave velocity (Vs) profiles. This paper describes its use in offshore geotechnical investigations (underwater MASW - UMASW) where the focus was on the upper 15 m of the sediment profile to aid the design of structures such as marine pipelines, cable routes and shallow anchor systems. UMASW was shown to provide reliable data in Irish offshore conditions in water depths of up to 50 m. The receiver spacing and array length, rather than the characteristics of the air gun seismic energy source, were the primary control on signal penetration and resolution of individual sediment layers. Good resolution of the properties of the upper 5 m of sediment was found by reducing the receiver spacing to as low as 0.3 m. A test site, with a broad intertidal zone, allowed coincident land, marine and direct measurements to be compared and Vs profiles obtained from UMASW, onshore MASW and by seismic cone testing (SCPTU) were in good agreement. Vs profiles estimated from published correlations with CPTU data in sandy sediments agreed well with the measured values. Inversion of data using different software packages showed only a minor variation in results.
Highlights Focus of work on top 15 m of offshore sediment. Obtained good data in harsh conditions to water depth of 50 m offshore western Ireland. Showed receiver spacing much more important than seismic source in resolving Vs in near bed offshore sediments. Showed good agreement in Vs profiles obtained from offshore UMASW, onshore MASW and by seismic cone testing (SCPTU). Any relatively low volume air gun source (12 in3 or similar) contains sufficient bandwidth for use in environments similar to those described here. Obtained very similar Vs profiles with two different inversion software codes.
Multichannel analysis of surface waves (MASW) for offshore geotechnical investigations
Long, Michael (author) / Trafford, Andy (author) / McGrath, Tomás (author) / O'Connor, Peter (author)
Engineering Geology ; 272
2020-04-23
Article (Journal)
Electronic Resource
English
Characterization of geotechnical sites by multichannel analysis of surface waves (MASW) method
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