Dave Giles

Airborne remote sensing for landslide hazard assessment: a case study on the Jurassic escarpment slopes of Worcestershire, UK

This paper describes the application of airborne remote sensing to the study of landslides on the clay-dominated slopes of the Cotswolds Hills between the towns of Broadway, Worcestershire, and Snowshill, Gloucestershire, in the UK. The project involved an initial desk study, airphoto interpretation and field survey in order to provide detailed information about the nature and extent of the landsliding in the area. High-resolution Airborne Thematic Mapper (ATM) imagery was acquired by the NERC Airborne Remote Sensing Facility, which was subsequently processed in order to develop a remote sensing method for landslide identification using airborne multispectral data. A range of image processing methods are described including colour composite enhancement and thermal imaging, while the focus of the paper will be on the development of a semi-automated method of landslide identification using image classification and texture analysis. Results from the first stage of the study have shown that the use of image processing techniques such as colour composites and thermal imaging can provide information on the ground surface not visible in conventional aerial photography. In this case study, this has included more detailed geomorphological information on landsides in the area and the nature of the cambering and gulls at the top of the escarpment. The second part of the study has investigated the use of image texture enhancement as a method of landslide identification, applied in isolation and incorporated into an image classification scheme as a semi-automated method of landslide identification. Results from this investigation indicate that landslides can be identified automatically with a high degree of accuracy (83%) and that by using image texture, the image classification technique is able to successfully differentiate between areas of landslide activity and stable slopes in the airborne imagery. Its is clear from the results of this study that in order to identify landslides in these types of clay-dominated terrains, image texture must be used. Inland landslides, like those on the Cotswolds escarpment, do not have a spectral signature but they do exhibit a distinct spatial signature that allows them to be identified in airborne imagery using textural analysis. The semi-automated method of landslide identification described in this paper represents a rapid method of terrain evaluation and landslide hazard assessment, which can be undertaken prior to more detailed field mapping.

Chapter 3 Geomorphological framework: glacial and periglacial sediments, structures and landforms

Abstract The development of the conceptual ground model (CGM) is a critical component of any desk study or ground engineering project planning process. A key task of the engineering geologist is to develop the CGM in order to predict the occurrence of known terrain units, elements and facets within a given landsystem, and to communicate the lateral and vertical variability of engineering rocks and soils found within that system. This chapter details the significant ground components of glacial and periglacial landsystems within a geomorphological framework describing the sediments, structures and landforms that could reasonably be expected to be encountered in these terrains. Examples are provided of both modern and relict glacial and periglacial landforms, their mode of formation and their field recognition. Glaciogenic and periglacial sediments are described both in terms of their sedimentological and formal engineering description. The chapter provides a suggested naming nomenclature for these sediments that can be used within a BS 5930 description. An extensive photoglossary is presented as a field aide memoir, enabling the engineering geologist to identify these features once on site.

Chapter 6 Material properties and geohazards

Abstract In engineering terms, all materials deposited as a result of glacial and periglacial processes are transported soils. Many of these deposits have engineering characteristics that differ from those of water-lain sediments. In the UK, the most extensive glacial and periglacial deposits are tills. Previously, engineering geologists have classified them geotechnically as lodgement, melt-out, flow and deformation tills, or as variants of these. However, in this book tills have been reclassified as: subglacial traction till, glaciotectonite and supraglacial mass-flow diamicton/glaciogenic debris-flow deposits (see Chapter 4, Sections 4.1–4.3). Because this classification is new, it is not possible to relate geotechnical properties and characteristics to the subdivisions of the new classification. Consequently, the domain/stratigraphic classification, recently developed by the British Geological Survey and others, has been used and their geotechnical properties and characteristics are discussed on this basis. The geotechnical properties and characteristics of the other main glacial and periglacial deposits are also discussed. For some of these (e.g. glaciolacustrine deposits, quick clays and loess), geohazards relating to the lithology and/or fabric of the deposit are discussed along with their properties. Other geohazards that do not relate to lithology and/or fabric are discussed separately as either local or regional geohazards. In some cases (e.g. glaciofluvial sands and gravels), the geotechnical properties and behaviour are similar to sediments deposited under different climatic conditions; these deposits are therefore not discussed at length. Similarly, some of the local geohazards that are found associated with glacial and periglacial deposits relate to current climatic conditions and are not discussed here. Examples include landsliding and highly compressible organic soils (peats).

Chapter 9 Conclusions and illustrative case studies

Abstract Engineering geology is inter alia concerned with the application of geology to the civil engineering industry to ensure safe and economic design and construction. It is a discipline that advances through practice, and case studies of both successes and failures are critical to its development. In this concluding chapter, 19 case studies have been compiled, mainly by those who were directly involved in the projects, to illustrate the nature and complexity of the ground conditions that can be encountered when working in relict glacial and periglacial terrain. The chapter finishes with a section on how the Working Party volume as a whole can be used to guide and improve best practice.

Modelling uncertainties in the stationary seepage problem

This paper considers the uncertainties in the stationary seepage problem. Initially, this investigation considers the uncertainties in the results of a finite element method analysis of a stationary seepage problem, where the properties of the porous medium can be considered as random variables. Random field theory is introduced to describe the uncertainty in the hydraulic properties of a porous media. The method of updating of stochastic random fields, under the condition that some of their sample realisations are observed and known is outlined. 1 Introduction In the modelling of seepage problems in porous media many kinds of simplifications are used which can introduce uncertainty into the results of the analysis, as illustrated by the following examples; (i) hydraulic characteristics can be considered a

Probabilistic Risk Assessment: The Tool For Uncertainty Reduction In Geotechnical Engineering

During last two decades many earth structures have encountered problems concerning their safety and reliability. Many of these difficulties arise due to an insufficient understanding of the uncertainties concerned with both their design and construction. Increased attention is now being given to risk and uncertainty in geotechnical engineering, driven by the pressure for improved reliability and safety. Geotechnical engineering is an interesting context in which to develop and apply ideas of uncertainty management. The Engineer is confronted with uncertainty associated with the random nature, spatial variability and inadequate characterization of geotechnical properties and in the complexity of the associated engineering projects. The Engineer is expected to make dependable and clear decisions often based on incomplete data sets. To do so requires an understanding of the nature of uncertainty and of appropriate techniques to manage and reduce it. This paper includes a brief description of recent probabilistic tools affecting reliability and probabilistic modelling of earth structures. 1 Introduction Any representation or characterization of the geotechnical media is sullied with uncertainties due to the inherent heterogeneity with these media and in the limitations within the objective or subjective methods, which are used to characterize them. Results of tests performed at different points of the medium could be considered as independent outcomes of the same experiment. ...