R.L. Terrington

Benefits of a 3D geological model for major tunnelling works : an example from Farringdon, east-central London, UK

In the design of major construction works, the better the ground conditions are known, the more control there is on the assessment of risks for construction, contract and personnel, and ultimately on final costs. Understanding of the ground conditions is usually expressed as a conceptual ground model that is informed by the results of desk study and of dedicated ground investigation. Using the GSI3D software, a 3D geological model (a model composed of attributed solid volumes, rather than of surfaces) can be constructed that exactly honours geologists’ interpretations of the data. The data are used in their true 3D position. The 3D model of faulted Lambeth Group (Palaeogene) strata in the area of the proposed new Crossrail Farringdon underground station, in central London, has several types of benefit. These include allowing optimum use of available ground investigation data, including third party data, with confidence. The model provides an understanding of the local geological structure that had not been possible using other commonly used methods: in particular, it shows the likely distribution of numerous water-bearing coarse deposits and their faulted offsets, which has potentially significant effects on groundwater control. The model can help to focus ground investigation, constrain design and control risk.

Reconstructing flood basalt lava flows in three dimensions using terrestrial laser scanning

We present a new method for reconstructing flood basalt lava flows from outcrop data, using terrestrial laser scanning (TLS) to generate three-dimensional (3D) models. Case studies are presented from the Faroe Islands and the Isle of Skye (UK), both part of the North Atlantic Igneous Province (NAIP). These were analyzed to pick out lava flow tops and bases, as well as dykes, lava tubes, and sedimentary layers. Three-dimensional surfaces were then generated using modeling software, and 3D geological models constructed. Finally, the models were interrogated to give data on flow thickness and crust-to-core ratio. The aim of this research is to obtain quantitative data on the internal heterogeneity of a sequence of flood basalt lava flows, and to provide high-resolution information about flow geometries and volcanic facies variations in 3D. Lava flow sequences display complex stacking patterns, and these are difficult to understand from photos or outcrop observations. Laser scanning allows us to study inaccessible outcrops, while avoiding the perspective distortion in conventional photography. The data from this study will form parts of larger models of flood basalt provinces, which will be used to improve seismic imaging in areas of basalt cover, and aid our understanding of facies architecture in flood basalts.

Modelling Volume Change Potential in the London Clay

Abstract The London Clay Formation is particularly susceptible to shrink–swell behaviour that has resulted in a long history of foundation damage owing to ground movement across the outcrop. Damage has cost up to £500 million in a single year. Underlying most of the Greater London area, the London Clay Formation is of major engineering importance as it is on and within this formation that the majority of the citys infrastructure, buildings and underground services are constructed. The Volume Change Potential (VCP) of a soil is the relative change in volume to be expected with changes in soil moisture content, and the subsequent shrinkage or swelling can cause major damage to structures above or below ground. Detailed statistical and spatial analyses of data across the London Clay outcrop have revealed a significant geographical trend in the VCP of this deposit, confirming an overall increase from west to east, but also showing subtle trends with depth. This paper describes how this analysis was carried out and shows how such assessments can yield valuable information about shrink–swell behaviour not only of the London Clay but also of similar shrink–swell-prone argillaceous formations elsewhere.

Why 3D? The Need for Solution Based Modeling in a National Geoscience Organization.

In recent years national geoscience organizations have increasingly utilized 3D model data as an output to the stakeholder community. Advances in both software and hardware have led to an increasing use of 3D depictions of geoscience data alongside the standard 2D data formats such as maps and GIS data. By characterizing geoscience data in 3D, knowledge transfer between geoscientists and stakeholders is improved as the mindset and thought processes are communicated more effectively in a 3D model than in a 2D flat file format. 3D models allow the user to understand the conceptual basis of the 2D data and aids the decision making process at local, regional and national scales. Some of these issues include foundation and engineering conditions, ground water vulnerability, aquifer recharge and flow, and resource extraction and storage. The British Geological Survey has established a mechanism and infrastructure through the Digital Geoscience Spatial Model Programme (DGSM) to produce these types of 3D geoscien...

Engineering Geological, Geotechnical and Geohazard Modelling for Offshore Abu Dhabi, UAE

This paper presents the development of an engineering geological, geotechnical and geohazard model for four oil and gas fields offshore of Abu Dhabi in the Arabian Gulf. The purpose of the model was to characterize the shallow ground conditions for the design of offshore platforms and other infrastructure. The model was developed based on the interpretation of nearly 60 years of ground engineering data including a vast amount of boreholes, laboratory test and cone penetration test data. Carbonate-rich sediments dominate the shallow geology of Abu Dhabi offshore region. The main lithological units of Miocene to Pleistocene age comprise weak carbonate rocks, calcarenite and calcisiltite, with frequent lenses and pockets of gypsum. These units are overlain by recent carbonate marine deposits. The geological models for the region were developed using the software package GSI3D™. Geostatistical methods were applied in the treatment of geological uncertainty in the model, and the analysis of the associated geotechnical design recommendations. The model also includes a detailed review of local and regional natural hazards, including seismic and submarine geohazards, with the potential to affect existing and proposed offshore infrastructure. Interrogation of the model enables effective decision-making on oil and gas development issues related to offshore ground investigation for the siting of new developments. This model can allow these works to be optimized at the advanced stages of planning, saving on time, cost and significantly reducing health, safety and environmental risks.