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Quarterly Journal of Engineering Geology & Hydrogeology

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Shear wave velocity monitoring of collapsible loessic brickearth soil

^{1 1}British Geological Survey, Kingsley Dunham Centre, Keyworth, Nottingham, NG12 5GG UK(e-mail: dgu@bgs.ac.uk)
^{2 2}Civil Engineering, School of Engineering, The University of Birmingham, Edgbaston, Birmingham, B15 2TT UK
^{3 3}Department of Civil and Building Engineering, Loughborough University, Loughborough,Leicestershire, LE11 3TU UK

Metastable loessic brickearth comprises a stiff fabric structure with inter-particle interactions different to those normally associated with clay-sized or silt-sized particle fabrics. Laboratory samples loaded near in situ moisture contents exhibited little consolidation and relatively high shear wave velocities, which changed in response to sample flooding. In situ hydro-collapse caused non-monotonic changes in the velocity of shear waves through loessic brickearth that was subjected to simple flooding and to flooding while under additional surface loading. Hydro-collapse in situ resulted in an overall reduction of up to 50% in the shear wave velocity. A conceptual model of brickearth structure based on SEM images is presented to explain the process of collapse and its effect on shear wave velocity. These indicate a transition from a relatively low-density, high-stiffness fabric to the higher-density, lower-stiffness fabric during structural collapse of the loessic brickearth. The collapse process disrupts clay bridge-bonds that hold individual and aggregated clay-coated silt sized particles in an open packed structure, and which are absent in a more closely packed collapsed structure. These studies provide information for geohazard research and the development of shear wave velocity and other geophysical tools to assess soil collapse potential in situ.

Key Words: density • engineering properties • geophysics • load tests • stiffness

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