Amodel of electrical conduction through clay-coated, silt-sized quartz-grains inter-connected by clay-bridges (e.g. brickearth) is developed. Underpinned by SEM studies of brickearth, the model predicts resistivity to be proportional to the size of the quartz-grains, where the resistance afforded by clay grain-coatings and clay-bridges is comparable. The model accommodates resistivity that increases through bridge breakage and decreases through bridge compression. The resistivity of in-situ undisturbed brickearth was found to be in the range 15 to 35 ohm-m. At such low values we demonstrate that electrical flow is dominated by conduction within clay-coatings and their interconnecting clay-bridges, rather than in mobile pore-water. A small electrode array, buried at shallow depth beneath the load plate (1.0 m by 1.0 m) of a field collapse experiment, monitored resistivity to a depth of 1.5 m over a 260 hour period. While the water level beneath the load plate remained below 1.0 m depth, the resulting 3D inverted resistivity models detected water injected immediately beneath the plate; recording rapid increases, in stages over 90 minutes, in the depth interval 0.45 to 0.75 m directly under the plate, during what appears to be collapse. These increases are attributed to breaking of clay-bridges weakened by injected water.
The report describes the field observations, sampling and geotechnical laboratory results on selected Scottish till sections in the Nairn-Cawdor area, Inverness-shire, Scotland. The first part of the report introduces the project and the context of this particular work. This is followed in Part 2 by an account of the sampling and testing methods undertaken for both geotechnical characterisation in the laboratory and micromorphology analyses. Part 3 provides an account of the location details of the logged and sampled exposures and descriptions of the lithological sequences at each site. Part 4 presents details and results of the characterisation tests (particle size analyses) undertaken on the collected geotechnical samples. The results of micromorphological analyses undertaken on thin sections prepared from ‘undisturbed’ samples acquired from this study are being described in a separate report.
The main part of this report describes the development history, structure and content of the BGS
National Geotechnical Properties Database, with a final section describing planned future
developments to enhance ease of access to, and promote wider use of, the database information
for a variety of applications.
The National Geotechnical Properties Database primarily holds geotechnical information
extracted from site investigation records provided by clients, consultants and contractors, and
from field and, secondarily, from laboratory test results carried out by the British Geological
Survey. Information held within the database includes locations to British National Grid
Coordinates; borehole, core and in situ test data; sample data; and a range of laboratory index,
mechanical properties and chemical test data on soils, rocks and water. The database tables and
fields are designed to be compatible with data supplied in the Association of Geotechnical and
Geoenvironmental Specialists (AGS) industry standard digital transfer format, enabling rapid
addition of data electronically, in addition to manual entry of analogue legacy data. This
information forms the basis for the geotechnical attribution of the 2D and 3D digital geological
models and underpins BGS core and commissioned engineering geology research. It also
provides an important information resource for external customers and internal/external
enquiries.
The role of Geotechnical Database Manager has been undertaken by Suzanne Self since 2000.
The British Geological Survey has undertaken a programme of research on landslide hazard mapping under support from the Department for International Development. The aim of the studies has been to develop a generic approach to landslide hazard modelling that can be applied and adapted in developing countries worldwide. The overall goal of the research is to prevent or minimise the loss of life and damage to property, infrastructure and livelihoods caused by landslides. To this end, case studies in four countries have been used to develop a rapid, inexpensive method for the production of regional landslide hazard maps. This report presents specific results and findings from the Slovakian study area in the Javorniky Mountains. The report is aimed at people and organisations in Slovakiathat are concerned with, or affected by, landslides. It discusses local issues that affect the development of landslide hazard preparedness strategies in individual countries. The accompanying map is a first attempt at mapping the regional landslide hazard in this part of Slovakia. It can be improved through additional local knowledge and the incorporation of more data on possible controlling factors, for example. Ultimately, the success of the project can only be judged by the take up, use and development of the hazard map in Slovakia.
In 1993 the Department of the Environment commissioned
the British Geological Survey in association with Entec UK
Ltd to undertake a three year study to develop techniques
for the synthesis and presentation of earth science information in a form which can be used readily and directly by planners and developers, and by those interested in conservation, and to provide a general introduction to the geological factors most relevant to planning and development in the City of Bradford Metropolitan District (CBMD.
The main objectives of the study were to:
collect and collate earth science information of relevance
to planners, developers, engineers and conservation
interests;
produce a set of thematic maps on applied geological
topics which will assist planning of land use,
development and conservation in the study area;
produce a summary map showing the main earth science
factors relevant to planning and development in the area;
provide two reports, one for non-specialists and the other
for those with specific technical knowledge in the fields
of geology, hydrogeology, engineering geology and
mineral resources.
Mineralogical and petrographical investigation of two loessic brickearth profiles from Ospringe and Peg- well Bay in north Kent, UK have differentiated two types of brickearth fabric that can be correlated with different engineering behaviour. Both sequences comprise meta- stable (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 be- tween the two units. A palaeosol is developed on the cal- careous brickearth, and is associated with the formation of rhizolithic calcrete indicating an arid or semi-arid envi- ronment. No evidence has been found for decalcification being responsible for the fabric of the upper 'non-cal- careous' 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 char- acterised 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
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