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- PublicationRapid, cost effective and accurate determination of in situ stiffness using MASW at BothkennarThe measurement of the small strain shear modulus, Gmax of a soil is important for a range of geotechnical design applications. This usually involves strains of 10-3 % and less. According to elastic theory Gmax can be calculated from the shear wave velocity. Recently several researchers e.g. Donohue et al. (2003, 2004), Long and Donohue (2007) and Park et al. (1999) have shown that Vs (and hence Gmax) can be obtained cheaply and reliably using the Multichannel Analysis of Surface Waves (MASW) method. An opportunity arose to test and further assesses the technique at the UK National soft clay research site at Bothkennar. The purpose of this note is to summarise the data recorded and to compare the resulting Vs measurements to other parallel data.
- PublicationMulti-method geophysical mapping of quick clayMarine clay deposits in coastal, post-submarine areas of Scandinavia and North America may be subjected to quick clay landslides and hence significant efforts are being taken to map their occurrence and extent. The purpose of this paper is to assess the use of a number of geophysical techniques for identifying quick clay. The investigated area, Smørgrav, located in southern Norway has a history of quick clay sliding, the most recent event occurring in 1984. Geophysical techniques that are used include electromagnetic conductivity mapping, electrical resistivity tomography, seismic refraction and multichannel analysis of surface waves. These results are compared to geotechnical data from bore samples, rotary pressure soundings and cone penetration testing. A number of these approaches have proved promising for identifying quick clay, in particular electrical resistivity tomography and electromagnetics, which delineated a zone of quick clay that had previously been confirmed by rotary pressure soundings and sampling. Seismic refraction was useful for determining the sediment distribution as well as for indicating the presence of shallow bedrock whereas the multichannel analysis of surface-waves approach suggested differences between the intact stiffness of quick and unleached clay. It is observed that quick clay investigations using discrete rotary pressure soundings can be significantly enhanced by using, in particular, electrical resistivity tomography profiles to link together the information between test locations, perhaps significantly reducing the need for large numbers of soundings.
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