M.G. Culshaw

From concept towards reality : developing the attributed 3D geological model of the shallow subsurface

In recent years, engineering geology has been trying to redefine itself in terms of a set of ‘core values’ or ‘special scientific principles.’ John Knill (2003) illustrated the essence of engineering geology in the engineering geological triangle. One way of trying to understand the relationships between some of the ‘core values’ is through the engineering geological ground model, which seeks to combine understanding of the spatial distribution of engineering boundaries with knowledge of rock and soil material, and mass, properties and the geological processes that alter these through time. The rapid development in information technology over the last twenty years and the digitization of increasing amounts of geological data has brought engineering geology to a situation in which the production of meaningful 3D spatial models of the shallow subsurface is feasible. The paper describes how this can be done and points the way to the next stage that involves the attribution of these spatial models with physical, mechanical and chemical property data. Some new developments in the provision of geohazard susceptibility information at the national scale are also discussed. A future is proposed in which site investigation sets out to test a pre-existing spatial model based on real data, rather than trying to create such a model based on concepts alone.

Natural and artificial cavities as ground engineering hazards

Abstract The occurrences of natural and artificial cavities are reviewed and their causes are assessed. Natural cavities are found principally in carbonate rocks and the processes of sinkhole formation are described. Solution cavities in non-carbonate rocks and cavities in insoluble rocks are also considered. Extraction methods for coal, metalliferous minerals and salts are described in relation to the creation of underground cavities. An outline procedure for locating cavities emphasizes the importance of the desk study in this type of investigation and the difficulty of proving the absence of cavities beneath a site.

Classification of artificial (man-made) ground

Abstract The legacy inherited from anthropogenic processes needs to be addressed in order to provide reliable and up-to-date ground information relevant to development and regeneration in the urban environment. The legacy includes voids as well as anthropogenic deposits (artificial ground). Their characteristics derive from former quarrying and mining activities industrial processes creating derelict ground, variably consolidated made ground, and contaminated groundwater and soils. All need to be systematically assessed to inform the planning process and provide the basis for engineering solutions. Site-specific investigation needs to be conducted on the back of good quality geoscientific data. This comes from ‘field’ survey, remotely sensed data interpretation, historical maps, soil geochemical sampling, and geotechnical investigation. Three-dimensional and, in the future, four dimensional, characterization of superficial deposits is required to reach an understanding of the potential spatial lithological variability of artificial ground and the geometry of important surfaces, i.e. the boundary conditions. The classification scheme for artificial ground outlined in this paper and adopted by the British Geological Survey, will help in achieving this understanding.

The use of geophysical surveying methods in the detection of natural cavities and mineshafts

Summary The use of geophysical methods for the location of cavities and mineshafts is reviewed in relation to engineering problems at the site investigation stage. Their success is limited by the resolution and penetration achieved by the particular method applied in a given situation. It is shown that no one single geophysical method will provide the answer to all the problems associated with cavity location but considerable improvement can be achieved by the application of several methods to a given problem. It is suggested that for most standard geophysical methods it is possible to detect a cavity whose depth of burial is less than twice its effective diameter. The concept of effective diameter is shown to be of considerable importance since the presence of the cavity or mineshaft does affect the physical properties of the surrounding rock mass and, hence, gives rise to a far larger anomalous zone than that produced by the cavity on its own.

The national landslide database of Great Britain: development, evolution and applications

Landslide inventories are essential because they provide the basis for predictive landslide hazard and susceptibility assessments and because they allow for the manipulation and storage of temporal and spatial data. The National Landslide Database has been developed by the British Geological Survey (BGS). It is the most extensive source of information on landslides in Great Britain with over 15,000 records of landslide events each documented as fully as possible. This information is invaluable for planners and developers as it helps them investigate, avoid or mitigate areas of unstable ground in accordance with Government planning policy guidelines. Therefore, it is vital that the continual verification, collection and updating of landslide information is carried out as part of the Survey’s ‘National Capability’ work. This paper describes the evolution from a static database to one that is continually updated forming part of a suite of national digital hazard products. The history of the National Landslide Database and associated Geographical Information System (GIS) is discussed, together with its application and future development.

A review of selected engineering geological characteristics of English Chalk

Abstract Chalk is a variable material, the properties of which are dependent upon its composition, textural features and diagenetic history. With the exception of certain horizons in the Lower Chalk that contain appreciable amounts of clayey material, the English Chalk is a remarkably pure micritic carbonate rock that generally can be divided into coarse and fine fractions. The latter comprises 70–80% of chalk. Cementation took place more or less contemporaneously with deposition so that the sediment was able to support relatively high overburden pressures. Hence, high values of porosity were retained. Chalk varies appreciably in density and hardness. The harder chalks are the result of diagenetic processes and bioturbation that brought about densification. In soft chalks the grains are only bound together at the points of contact by thin films of calcite. The latest classification of chalk is based on an assessment of intact dry density, discontinuity aperture and discontinuity spacing. Chalk tends to vary from moderately weak to moderately strong and its strength is significantly reduced on saturation. Under triaxial loading conditions diagonal shear failure tends to occur at lower confining pressures but at higher confining pressures barrel-shaped failure occurs indicating plastic deformation and textural disaggregation. Similarly, at low loading, chalk exhibits low volume compressibility but much more significant consolidation occurs if the yield stress is exceeded. Chalk undergoes dissolution and so solution features are found throughout its outcrop. Mineworkings in the Chalk extend back into the distant past, the most ancient being those excavated in the Neolithic Age for flint. Several types of workings exist. Collapse of old mineworkings, most of which are unrecorded, is difficult to predict. The potential for subsidence, caused by the collapse of both mineworkings and dissolution features, affects development and its occurrence can lead to the abandonment of property or, worse, the loss of lives.

Petrographic and engineering properties of sandstones from the Sneinton Formation, Nottinghamshire, England

Abstract The Sneinton Formation occurs at the base of the Mercia Mudstone Group and consists of sandstones with interbedded siltstones and mudstones. The sample material was obtained from core from a 63 m deep borehole sunk near Epperstone some 10 km north of Nottingham. The petrographic characteristics, namely quartz content, clay size content, packing density and particle size distribution of the sandstones, were determined for a series of depths. In addition, the density, porosity, compressive and indirect tensile strengths, hardness, modulus of deformation, Poissons ratio and slake durability index were determined for the same depth intervals. The petrographic characteristics then were correlated with the physical and mechanical properties and the significance of the relationships assessed by Students t value. The individual physical and mechanical properties also were the correlated with each other and the significance of the relationships similarly assessed.

A geotechnical survey of some British Coal Measures mudstones, with particular emphasis on durability

Abstract Samples of fresh mudstones were obtained from near Tow Law and Kirkheaton, and of weathered mudstones from near Wrexham. The mineral composition of these mudstones was similar, kaolinite being the principal clay mineral, the clay mineral fraction dominating. Quartz was the chief non-clay mineral present. Some basic geotechnical and index properties were determined. The fresh mudstones from near Tow Law had a low plasticity, as did the moderately and highly weathered mudstones from near Wrexham. However, the completely weathered mudstones from the latter area possessed intermediate plasticity. The strength of the fresh mudstones from near Kirkheaton was notably higher than that of the mudstones from near Tow Law. Both groups of fresh mudstones displayed significant anisotropy ratios when they underwent axial and diametral point load testing. This, no doubt, was due to the influence of lamination. As durability is one of the most important engineering properties of mudstone, it was assessed by a number of tests. One cycle slake durability testing did not appear to offer an acceptable indication of the durability of mudstones when compared with cyclic wetting and drying, cyclic freezing and thawing, and geodurability classification. Cyclic slake durability testing and comparison with unconfined compressive strength would seem to be a more reliable way of determining durability. Both fresh and weathered mudstones underwent little expansion when subjected to swelling tests. However, in the case of the weathered mudstones, the amount of swelling stress and strain could be related to basic geotechnical properties.

Landslide management in the UK—the problem of managing hazards in a ‘low-risk’ environment

The UK is a country with limited direct experience of natural disasters. Whilst landslide losses are not negligible and fatalities are rare, accounts are under-reported. Financial losses from landslides are poorly understood but likely to be considerably in excess of £10 million per year. As a result, a strategic management framework has evolved based upon small, low-impact events punctuated by occasional larger events or larger landslides affecting urban areas. We present an overview of the different landslide management mechanisms in the UK and discuss them in context of cases studies to explore their effectiveness. We conclude with three issues that may have implications for landslide management in the UK and other ‘low-risk’ countries. Firstly, the evidence base by which landslide hazards and risks are measured is insufficient and limitations in existing information need to be better understood. Secondly, existing guidance on strategic and responsive management needs to be assessed for its fitness for purpose. Thirdly, we encourage debate about the importance of near misses.

Engineering Geology for Tomorrow’s Cities

This book and the accompanying CD-ROM provide a statement of our knowledge and understanding of engineering geology as applied to the urban environment at the start of the 21st century. In particular, this volume demonstrates that: * working standards originally developed nationally are becoming internationalized; * risk assessment, rather than just assessment of hazards, is driving decision-making; * geo-environmental change, whether climatically or anthropogenically driven, is becoming better understood; * greater use of underground space is being made; * the relentless advance of information technology is providing new opportunities for engineering geologists to interpret and visualize the subsurface. This book shows that in developed and developing countries alike, engineering geolgists are increasingly exchanging ideas and learning from each other in a genuine two-way process. These ideas will contribute significantly to the sustainable development of both new and long-established urban environments world-wide.