Shear wave velocity monitoring of collapsible loessic brickearth soil

• Published in: Quarterly journal of engineering geology and hydrogeology 2006-05, Vol.39 (2), p.173-188
• Main Authors: Gunn, D. A, Nelder, L. M, Jackson, P. D, Northmore, K. J, Entwisle, D. C, Milodowski, A. E, Boardman, D. I, Zourmpakis, A, Rogers, C. D. F, Jefferson, I, Dixon, N
• Format: Article
• Language: English
• Subjects: body waves; bonding; brick earth; clastic sediments; clay; clay bridges; consolidation; consolidometers; Earth sciences; Earth, ocean, space; elastic waves; Engineering and environment geology. Geothermics; Engineering geology; engineering properties; England; Europe; Exact sciences and technology; geologic hazards; Great Britain; in situ; Kent England; laboratory studies; load tests; loading; loess; moisture; monitoring; Ospringe England; packing; piezoelectric properties; S-waves; sediments; seismic waves; shear strength; silt; soil mechanics; soils; stiffness; theoretical models; United Kingdom; velocity; Western Europe
• ISSN: 1470-9236; 2041-4803
• DOI: 10.1144/1470-9236/04-045

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.