Engineering geology maps of the UK

School and university students of geology, engineering geology and geotechnical engineering generally have less knowledge of engineering geological conditions than those who have had experience of hands-on research or practice. In the UK, the number of geology, geoscience and earth science departments has reduced over the past 25 years. Engineering geology has a very weak academic base and geology is taught less to civil engineering students than previously

The mineralogy and fabric of 'Brickearths' in Kent, UK and their relationship to engineering behaviour

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 interped 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 structure and operation of the BGS National Geotechnical Properties Database. Version 2

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

In-situ investigation of problematical soils

Problematical soils occur in many parts of the world, both naturally and as a result of man-made activity, thus making their behaviour a truly global problem. In-situ properties are often variable and difficult to predict, so effective site investigation is essential for the optimum characterisation and prediction of soil behaviour. Commonly, site investigations favour established techniques such as penetration tests, trial pits and boreholes. These provide useful but limited data, being obtained at discrete points on a site. Similarly, and as a consequence of disturbance, laboratory testing of soil samples often does not truly reflect the in-situ properties of the soil. The use of in-situ geophysical investigation is suggested as a possible solution to this problem. This paper highlights the potential of geophysics, with illustrated examples of recent work where geophysical methods have successfully assessed tropical red clay and brickearth soil properties. Information can be gained on both the general physical properties and the properties relating to failure of the soil (e.g. collapse or landslides), such as moisture content and presence of voids. It is also possible to assess the effectiveness of ground improvement engineering work undertaken on such soils. Geophysical investigations, characterising whole volumes of ground can be conducted rapidly and cost effectively, helping to provide the best approach to gain knowledge of in-situ collapsible soil conditions

Field observations and laboratory test results on tills in the Nairn-Inverness area of NE Scotland

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

Consequences of a modest loess fall over southern and midland England

Loess deposits that are invariably small are scattered over southern and midland England. They can be examined within a simple, speculative geomorphological model. This allows the concentration of loess material to be predicted and explained and a distribution network relating to the whole system produced. A complex series of events in the Weald loess trap causes a concentration of loess material by rivers flowing through various gaps in the Downs. The Thames provides loessic estuarine deposits , and the Pegwell Bay loess was a feature of the R.Stour. South coast accumulations are related to rivers flowing south through Downs gaps, such as the Adur and the Arun. The geomorphological model assumes a modest loess fall (say 20-50 cm, derived from the northeast) over southern and midland Britain, and develops loess accumulations by logical geomorphological processes from this starting point. Palaeoclimatic studies suggest that interest in the British loess is growing; some overall sedimentological studies might be useful. Loess in Britain should be seen as a major landscape material; it is often not an obvious landscape component but it is of fundamental importance. The distribution tree within the geomorphological model accommodates all relevant loess deposits, with major deposits falling on the ‘’main-line’ of significant events

New OSL dating of UK loess : indications of two phases of Late Glacial dust accretion in SE England and climate implications

Windblown dust deposits or loess, locally known in the UK as brickearth, blanket many parts of southern England outside the limits of the British and Irish Ice Sheet. The best-studied loess exposures occur in Kent, southeast England, where the deposits are believed to be Late Glacial in age. New sedimentological evidence is presented for phases of accretion with two distinct units, a calcareous brickearth exhibiting periglacial cryoturbation and a non-calcareous, massive brickearth. Optically stimulated luminescence (OSL) dating has been applied to chemically isolated modal quartz silts to derive a chronology for sediment accretion and to better understand the palaeoclimatic significance of these deposits

Engineering geology (bedrock) map of the United Kingdom

Engineering geology is a broad discipline within geology that is defined by the International Association for Engineering Geology and the Environment (IAEG) as: “... the science devoted to the investigation, study and solution of the engineering and environmental problems which may arise as the result of the interaction between geology and the works and activities of man as well as to the prediction of and the development of measures for prevention or remediation of geological hazards.” Engineering geology is important, therefore, in the maintenance of public health, safety and welfare during development and redevelopment of the earth’s surface and shallow subsurface, in safeguarding the geological aspects of the environment and in delivering economic benefit. Two engineering geological maps of the UK have been produced at a scale of 1:1 million. One map shows the engineering geological characteristics of the bedrock, that is, those soils and rocks that were in place before the Quaternary Period. The second map shows the engineering geological characteristics of the superficial deposits emplaced during approximately the last 2 million years in the Quaternary Period. The reason for this separation is that Quaternary materials cover about 60% of the UK’s surface and hence mask large parts of the earlier geology. However, they are often relatively thin (less than 10 m) so the bedrock is frequently intersected during building and construction. These maps should not be used for site specific purposes, their intention is to provide an introduction to the engineering geology of the UK by presenting a broad overview of how engineering geological conditions change across the country. They provide the first stage to understanding the consequences of the interaction between human development, the ground and the natural processes acting upon it. For further information regarding engineering geological hazards, GeoSure products and other BGS datasets visit the BGS website http://www.bgs.ac.uk/ or contact BGS Enquiries enquiries@ bgs.ac.uk