Marcus R. Dobbs

Methodology for creating national engineering geological maps of the UK

In the United Kingdom (UK) geological maps traditionally have been attributed with lithostratigraphical map units. However, without significant supplementary information, these maps can be only of limited use for planning and engineering works. During the middle part of the 20th century, as development of the science of engineering geology began to accelerate, engineering geological maps started to appear in various forms and at various scales to meet the challenge of making geological maps more suited to land-use planning, engineering design, building, construction and maintenance. Today, engineering geological maps are routinely used at various scales as part of the engineering planning, design and construction process. However, until recently there had been no comprehensive, readily available engineering geological map of the UK to provide the broad context for ground investigation. This paper describes the recently published (2011) 1:1 000 000 scale engineering geology superficial and bedrock maps of the UK. It describes the methodologies adopted for their creation and outlines their potential uses, limitations and future applications. Supplementary material: Engineering Geology (Bedrock) Map of the United Kingdom, Engineering Geology (Superficial) Map of the United Kingdom and Extended Key for the Engineering Geology Maps of the United Kingdom are available at http://www.geolsoc.org.uk/SUP18528.

Folded fabric tunes rock deformation and failure mode in the upper crust

The micro-mechanisms of brittle failure affect the bulk mechanical behaviour and permeability of crustal rocks. In low-porosity crystalline rocks, these mechanisms are related to mineralogy and fabric anisotropy, while confining pressure, temperature and strain rates regulate the transition from brittle to ductile behaviour. However, the effects of folded anisotropic fabrics, widespread in orogenic settings, on the mechanical behaviour of crustal rocks are largely unknown. Here we explore the deformation and failure behaviour of a representative folded gneiss, by combining the results of triaxial deformation experiments carried out while monitoring microseismicity with microstructural and damage proxies analyses. We show that folded crystalline rocks in upper crustal conditions exhibit dramatic strength heterogeneity and contrasting failure modes at identical confining pressure and room temperature, depending on the geometrical relationships between stress and two different anisotropies associated to the folded rock fabric. These anisotropies modulate the competition among quartz- and mica-dominated microscopic damage processes, resulting in transitional brittle to semi-brittle modes under P and T much lower than expected. This has significant implications on scales relevant to seismicity, energy resources, engineering applications and geohazards.

The Glasgow (Scotland) geotechnical GIS: a desk study tool

Abstract Desk study is an essential part of all civil engineering project ground investigations. It is usually a collation and review of existing data and information about a site and, in some cases, the surrounding area, and carried out at an early stage of the ground investigation to inform and guide the ground investigation. It should provide suitable data and information to assess the ground conditions and the implications for the proposed engineering design. A similar approach can be taken to inform local, regional or national government with regard to development and the redevelopment of urban areas where ground investigation data and information are available. This paper describes a spatially defined geotechnical information system (GIS) designed to provide geological, geotechnical and geoenvironmental data and information for Glasgow City Council (Scotland). The system contains three main parts: the geology (bedrock, Quaternary and artificial deposits and the thickness and depth of these deposits); the data are presented as various summary graphs illustrating the variation of various parameters as well as a geotechnical and geoenvironmental database; and tools specifically developed to present the data. As undermining is a hazard in part of Glasgow, a dataset showing the distribution of mining is included. Further interpretation of the characteristics of the geological units has produced an engineering geological classification which may be used to provide rapid assessment of the engineering geological conditions.