caa a22 4500 605454469 CHVBK 20210128100207.0 cr unu---uuuuu 210128e20151101xx s 000 0 eng 10.1007/s10064-014-0694-5 doi (NATIONALLICENCE)springer-10.1007/s10064-014-0694-5 The mineralogy and fabric of ‘Brickearths' in Kent, UK and their relationship to engineering behaviour [Elektronische Daten] [Antoni Milodowski, Kevin Northmore, Simon Kemp, David Entwisle, David Gunn, Peter Jackson, David Boardman, Aris Zoumpakis, Christopher Rogers, Neil Dixon, Ian Jefferson, Ian Smalley, Michèle Clarke] Mineralogical and petrographical investigation of two loessic brickearth profiles from Ospringe and Pegwell Bay in north Kent, UK have differentiated two types of brickearth fabric that can be correlated with different engineering behaviour. Both sequences comprise metastable (collapsing) calcareous brickearth, overlain by non-collapsing ‘non-calcareous' brickearth. This study has demonstrated that the two types of brickearth are discretely different sedimentary units, with different primary sedimentary characteristics and an erosional junction between the two units. A palaeosol is developed on the calcareous brickearth, and is associated with the formation of rhizolithic calcrete indicating an arid or semi-arid environment. No evidence has been found for decalcification being responsible for the fabric of the upper ‘non-calcareous' brickearth. Optically-stimulated dates lend further support for the calcareous and ‘non-calcareous' brickearth horizons being of different age or origins. The calcareous brickearth is metastable in that it undergoes rapid collapse settlement when wetted under applied stresses. It is characterised by an open-packed arrangement of clay-coated, silt-sized quartz particles and pelletised aggregate grains (peds) of compacted silt and clay, supported by an inter-ped matrix of loosely packed, silt/fine-grained sand, in which the grains are held in place by a skeletal framework of illuviated clay. The illuviated clay forms bridges and pillars separating and binding the dispersed component silt/sand grains. There is little direct grain-to-grain contact and the resultant fabric has a very high voids ratio. Any applied load is largely supported by these delicate clay bridge and pillar microfabrics. Collapse of this brickearth fabric can be explained by a sequence of processes involving: (1) dispersion and disruption of the grain-bridging clay on saturation, leading to initial rapid collapse of the loose-packed inter-ped silt/sand; (2) rearrangement and closer stacking of the compact aggregate silt/clay peds; (3) with increasing stress further consolidation may result from deformation and break up of the peds as they collapse into the inter-ped regions. Smectite is a significant component of the clay assemblage and will swell on wetting, further encouraging disruption and breaking of the clay bonds. In contrast, the ‘non-calcareous' brickearth already possesses a close-packed and interlocking arrangement of silt/sand grains with only limited scope for further consolidation under load. Minor authigenic calcite and dolomite may also form meniscus cements between silt grains. These have either acted as "scaffolds” on which illuviated clay has subsequently been deposited or have encrusted earlier-formed grain-bridging clay. In either case, the carbonate cements may help to reinforce the clay bridge fabrics. However, these carbonate features are a relatively minor feature and not an essential component of the collapsible brickearth fabric. Cryoturbation and micromorphological features indicate that the calcareous brickearth fabric has probably been developed through periglacial freeze-thaw processes. Freezing could have produced the compact silt/clay aggregates and an open porous soil framework containing significant inter-ped void space. Silt and clay were remobilised and translocated deeper into the soil profile by water percolating through the active layer of the sediment profile during thawing cycles, to form the loosed-packed inter-ped silt matrix and grain-bridging meniscus clay fabrics. In contrast, the upper ‘non-calcareous' brickearth may represent a head or solifluction deposit. Mass movement during solifluction will have destroyed any delicate grain-bridging clay microfabrics that may have been present in this material. The Author(s), 2015 Loess nationallicence Brickearth nationallicence Mineralogy nationallicence Fabric nationallicence Collapse behaviour nationallicence Palaeoenvironment nationallicence Milodowski Antoni British Geological Survey, Environmental Science Centre, Keyworth, NG12 5GG, Nottingham, UK aut Northmore Kevin British Geological Survey, Environmental Science Centre, Keyworth, NG12 5GG, Nottingham, UK aut Kemp Simon British Geological Survey, Environmental Science Centre, Keyworth, NG12 5GG, Nottingham, UK aut Entwisle David British Geological Survey, Environmental Science Centre, Keyworth, NG12 5GG, Nottingham, UK aut Gunn David British Geological Survey, Environmental Science Centre, Keyworth, NG12 5GG, Nottingham, UK aut Jackson Peter British Geological Survey, Environmental Science Centre, Keyworth, NG12 5GG, Nottingham, UK aut Boardman David School of Civil Engineering, The University of Birmingham, Edgbaston, B152TT, Birmingham, UK aut Zoumpakis Aris School of Civil Engineering, The University of Birmingham, Edgbaston, B152TT, Birmingham, UK aut Rogers Christopher School of Civil Engineering, The University of Birmingham, Edgbaston, B152TT, Birmingham, UK aut Dixon Neil School of Civil and Building Engineering, Loughborough University, LE11 3TU, Loughborough, Leicestershire, UK aut Jefferson Ian School of Civil Engineering, The University of Birmingham, Edgbaston, B152TT, Birmingham, UK aut Smalley Ian Department of Geography, Leicester University, LE1 7RH, Leicester, UK aut Clarke Michèle School of Geography, University of Nottingham, University Park, NG7 2RD, Nottingham, UK aut Bulletin of Engineering Geology and the Environment Springer Berlin Heidelberg 74/4(2015-11-01), 1187-1211 1435-9529 74:4<1187 2015 74 10064 https://doi.org/10.1007/s10064-014-0694-5 text/html Onlinezugriff via DOI BK010053 XK010053 XK010000 Metadata rights reserved Springer special CC-BY-NC licence nationallicence 1 research-article jats NATIONALLICENCE NATIONALLICENCE NL-springer NATIONALLICENCE 856 40 https://doi.org/10.1007/s10064-014-0694-5 text/html Onlinezugriff via DOI NATIONALLICENCE 700 1- Milodowski Antoni British Geological Survey, Environmental Science Centre, Keyworth, NG12 5GG, Nottingham, UK aut NATIONALLICENCE 700 1- Northmore Kevin British Geological Survey, Environmental Science Centre, Keyworth, NG12 5GG, Nottingham, UK aut NATIONALLICENCE 700 1- Kemp Simon British Geological Survey, Environmental Science Centre, Keyworth, NG12 5GG, Nottingham, UK aut NATIONALLICENCE 700 1- Entwisle David British Geological Survey, Environmental Science Centre, Keyworth, NG12 5GG, Nottingham, UK aut NATIONALLICENCE 700 1- Gunn David British Geological Survey, Environmental Science Centre, Keyworth, NG12 5GG, Nottingham, UK aut NATIONALLICENCE 700 1- Jackson Peter British Geological Survey, Environmental Science Centre, Keyworth, NG12 5GG, Nottingham, UK aut NATIONALLICENCE 700 1- Boardman David School of Civil Engineering, The University of Birmingham, Edgbaston, B152TT, Birmingham, UK aut NATIONALLICENCE 700 1- Zoumpakis Aris School of Civil Engineering, The University of Birmingham, Edgbaston, B152TT, Birmingham, UK aut NATIONALLICENCE 700 1- Rogers Christopher School of Civil Engineering, The University of Birmingham, Edgbaston, B152TT, Birmingham, UK aut NATIONALLICENCE 700 1- Dixon Neil School of Civil and Building Engineering, Loughborough University, LE11 3TU, Loughborough, Leicestershire, UK aut NATIONALLICENCE 700 1- Jefferson Ian School of Civil Engineering, The University of Birmingham, Edgbaston, B152TT, Birmingham, UK aut NATIONALLICENCE 700 1- Smalley Ian Department of Geography, Leicester University, LE1 7RH, Leicester, UK aut NATIONALLICENCE 700 1- Clarke Michèle School of Geography, University of Nottingham, University Park, NG7 2RD, Nottingham, UK aut NATIONALLICENCE 773 0- Bulletin of Engineering Geology and the Environment Springer Berlin Heidelberg 74/4(2015-11-01), 1187-1211 1435-9529 74:4<1187 2015 74 10064