Bedrock quality maps
SGU’s bedrock quality maps are primarily used to assess the best uses for different rocks, for example as aggregates for road and railway construction or concrete production; in the design of infrastructure, tunnel and rock chamber projects; and as an aid to local authorities, county administrative boards, companies and others responsible for planning sustainable use of natural resources.
At present, bedrock quality maps are available for parts of the Stockholm, Uppsala, Västerås, Eskilstuna, Örebro, Dalarna, Gävle–Hofors, Östergötland–Vimmerby and Göteborg regions. Surveys are under way in Sundsvall, Jönköping and parts of Skåne and southern Halland. These maps can be seen as a complement to SGU’s 1:50 000 scale bedrock maps.
Maps show technical properties of bedrock
Our bedrock quality maps show the technical properties of bedrock from the point of view of its use as aggregate or in civil engineering projects. Rocks are assigned to one of three quality classes: (1) good, (2) less good or (3) poor. In addition, deformation zones etc. are shown. For specific locations, the maps also provide more detailed information on technical properties of the bedrock and its natural gamma radiation, expressed in terms of a radium index and an activity index.
The information is available as a plotted map with an accompanying description, and in database form.
How the maps are produced
SGU’s bedrock quality maps are based on field examination of the larger rock units in an area, involving sampling for technical analysis, measurements of fractures and an assessment of fracture density. Based on the analyses performed, an areal interpretation of rock quality is undertaken. Thin sections of the samples are produced for petrographic analysis, and studies are made of grain size, grain size variation, grain boundaries and microfractures.
To assess a rock’s suitability as an aggregate for concrete, a study is made of its potential alkali-silica reactivity. SGU’s airborne geophysical maps, which show the magnetic field and bedrock electrical conductivity (VLF), are used together with elevation data to interpret zones of weakness in the bedrock.
Gamma radiation measurements of outcrops are carried out to identify areas with a risk of elevated radon levels. A radium index, reflecting the radium content of a material, is calculated; for building materials, this index should be below 1.0. According to recommendations from the Nordic countries’ radiation protection authorities, building materials should have an activity index of less than 2.
These various studies form the basis for an assessment of the suitability of the sampled rocks as aggregates for concrete, railways or roads.
All the data on bedrock quality, analysis results etc. are held in our bedrock quality database. Information on bedrock geology is entered into a bedrock database that comprises several components, including an outcrop database.
Enquiries and orders
For further information and orders, please contact Customer services:
SGU, Customer services, Box 670, SE-751 28 Uppsala
Tel: +46 18-17 90 00
Fax: +46 18-50 10 20
International Association for Engineering Geology and the Environment (IAEG), which has established an international Commission on Aggregates.