3D geoscience techniques improve understanding of what lies beneath
18 October 2016
Geoscience deals with the geology and subsurface of the earth and involves thinking in 3D. Geological maps are 2D efforts to convey 3D renditions of the subsurface that have tended towards cartoon-like conceptual sketches. Insufficient data and inherent complexity is frequently the cause of such poor understanding and representations. However, modern data collection techniques, coupled with powerful computer generated imagery, have greatly improved our ability to convey and better understand what lies beneath our feet.
Early geological maps were based on direct observation of rock and soil formations, usually as surface exposures in mountains, rivers, quarries and with limited underground exposures in road cuttings, caves, tunnels and mines. Ireland’s early geological mapping was carried out on a systematic scale from the mid-19th century, primarily driven by the search for coal and minerals.
The Geological Survey of Ireland (GSI) systematically mapped the entire island with field sheets on a scale of 1:10.560 (six inches to one mile), used to produce one inch to one mile maps. These maps and field sheets (now scanned and online) can still be accessed and are incredibly detailed and accurate.
Among the best examples of early mapping are the field sheets of George Victor Du Noyer (1817-1869) who often illustrated the rear and blank spaces of the sheets with beautiful sketches of the detailed geology or scenery.
The limited nature of surface exposure requires geologists to extrapolate and interpret to imagine and project what conditions exist at depth. Geoscientists now have, at their disposal, a vast amount of additional data to supplement visual observation. Geochemistry provides information of the chemical composition of soils and rocks. Samples can be taken from the surface, and with the help of drills from the subsurface, often to considerable depths. Geophysical data on magnetic, radiometric and density factors of the earth can be collected remotely by aircraft and satellite.
Satellite imagery has added greatly to our understanding of the earth and its processes, particularly for large scale structures or mapping in remote regions. An example of integrated data collection in Ireland is the Tellus project currently being carried out by GSI across Ireland. This involves the collection of airborne geophysical data using low flying aircraft and ground based geochemistry gathering stream and soil samples on a systematic basis.
Another example of data sets is the mapping of groundwater resources which supply approximately a third of Ireland’s water. The vulnerability of groundwater to pollution is determined by the amount of cover over the water bearing horizon (known as aquifers). Understanding the role of groundwater in flooding and flood management is central to GSI’s service to local authorities and the OPW.
The tsunami of new data available to geoscientists demands methodologies to manage the data so as to derive the maximum value from the information which has a wide range of uses. Geographic Informatuion Sysytems (GIS) or digital mapping capability enables 2D images for individual data sets can be overlain and easily manipulated as to scale and orientation
The advent of integrated Building Information Modelling (BIM) software has provided the ability to correlate spatial data related to building design in 3D; the adoption of similar techniques for subsurface data is a crucial step forward for geoscience.
3D modelling work at GSI is at the leading edge for presenting data on the subsurface and groundwater, generally at a large scale. Smaller scale 3D modelling for specific sites is provided by geodetic and geophysical surveyors. Analysis of 3D geological data allows geologists to answer specific questions about shape, orientation and volume of rock types in the subsurface, which in turn can help planners and policy makers make informed decisions. Visualisation can also be a powerful tool for education, as well as a means of producing eye catching material for public communication.
The GSI Land Mapping Unit is working on the creation of 3D geological models of the bedrock and Quaternary geology of Ireland. These models allow new insights into the nature and distribution of the geological units in the country. These models vary from a large scale model of the deep geology of Ireland, with cross sections linking across the Irish Sea to Britain, down to detailed subsurface models of Dublin and Cork (Fig 1, right), based on painstaking digital entry of over a thousand boreholes from the National Geotechnical Database.
Engineers are one of the leading users of 3D data, particularly in BIM which provide the modern blueprints for complex construction and development. GSI data can feed into these complex and detailed models, which are often of vital use for engineers and construction companies. GSI data is also shared with the scientific community and the general public using free viewers and 3D pdf files.
In this way, the user can interact with the geological model; view it in any orientation and scale, or if interested in more scientific information, create a synthetic borehole or draw a synthetic cross section. Models created for all of Ireland’s major towns are available to download for free from the GSI web site.
The GSI Groundwater programme has found that through a combination of 3D geological modelling and groundwater investigations, it is possible to develop complex 3D models showing how water flows through permeable rock underground (Fig 2, right). These ‘aquifer’ models reflect the hydrogeological properties of the bedrock and allow for the delineation of groundwater flow pathways in three dimensions.
GSI marine programme, which along with the Marine Institute delivers Ireland’s national seabed mapping programme, INFOMAR, has utilised 3D primarily to visualise and promote awareness of their Bathymetric (seafloor) data while the cartography unit have worked with geological mapping teams in adopting 3D technology for geology with all-Ireland geological visualisations and animations to be displayed at geoheritage sites such as the UNESCO Copper Coast Geopark in Waterford.
Correlating data can lead to a better understanding of:
- how and where mineral deposits are formed;
- how and where groundwater is in danger;
- how agricultural outputs and human health are effected by soil and rock composition;
- what areas are problematic for development e.g. susceptible to landslides and or soft ground conditions; and,
- how turloughs may respond to flood conditions.
About Geoscience Ireland
Geoscience Ireland comprises 28 member companies (including the GSI), provides geodetic, geophysical, geotechnical and geochemical datasets , assisting clients across a wide range of infrastructure developments. Since its inception four years ago, Geoscience Ireland companies now employ over 1,550 persons and in 2015 turned over €311 million. Formed in response to the crisis in Irish construction, Geoscience Ireland assists its members in wining work in international markets, assisted by GSI and Enterprise Ireland. Over 400 net new jobs have been created by Geoscience Ireland members up to July 2016.
Geoscience Ireland is delighted to again sponsor the Geoscience Award for the Engineers Ireland Excellence Awards 2016. The winner will be announced at the Excellence Awards dinner on Friday, November 4.http://www.engineersjournal.ie/2016/10/18/geoscience-ireland-excellence-awards/http://www.engineersjournal.ie/wp-content/uploads/2016/10/Geological-mapping-FEAT.jpghttp://www.engineersjournal.ie/wp-content/uploads/2016/10/Geological-mapping-FEAT-300x300.jpgCivil3D,BIM,geoscience,Geoscience Ireland,Ireland,OPW