is-2000-163_geoscientific information for environmental issues, with special emphasis on applied...

7/28/2019 Is-2000-163_Geoscientific Information for Environmental Issues, With Special Emphasis on Applied Bedrock Geolog

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GEOSCIENTIFIC INFORMATION FOR ENVIRONMENTAL

ISSUES, WITH SPECIAL EMPHASIS ON APPLIED BEDROCK

GEOLOGY IN SWEDEN

Lars Persson1

ABSTRACT

For society at large, geoscientific information is of vital importance. In particular this concerns mapsshowing natural resources such as ores, minerals, rock, groundwater, gravel, sand and clay, intended for usewhen planning, prospecting, exploiting, mining, and excavating. When the information is detailed andaccurate, right decisions can be taken which are crucial regarding environmental issues.

There is a growing demand in applied geology for thematic and environmental geological maps. The

Geological Survey of Sweden, SGU, has initiated projects to satisfy some of the above-mentioned needs.SGU therefore intends to produce geoscientific information concerning the most densely populated areas ofSweden. From this year (2000) investigations have been started in the Lake Mlaren area, including thecapital Stockholm, in the Gothenburg area on the west coast, and the MalmHelsingborg area in southwestSweden, opposite Denmark.

Bedrock quality aspects have been under development by SGU as a programme for about 5 years. Theinformation presented is continuously discussed with the users, consequently leading to better products.Bedrock quality implies the presentation of bedrock and its properties for the construction industry, both forthe use as construction material and for instance when planning tunnelling and other underground works.The latter has prompted the the development of 3D bedrock presentations providing geological andengineering geological information for underground works e.g. tunnels and caverns, especially in the

Stockholm metropolitan region. Bedrock Quality Maps are being produced; so far an area of 3,750 km

2

hasbeen investigated and during this year another 3,125 km2 are to be added. So far, mapping has been coveredin the Lake MlarenStockholm region and the Gothenburg municipality. These maps show how bedrockcan be used as aggregates for roads, railway trackbed and in concrete production.

The use of sand and gravel in Sweden is restricted in law for environmental reasons. The use of crushedbedrock, on the other hand, is increasing and at present amounts to about half of all aggregate materialproduced. Recycling of materials has also increased but is as yet of minor importance, as stocks of materialsare good. Inventories of bedrock are in great demand, not least for the optimal siting of quarries. The openingof new quarries should raise questions such as the uses for which the materials are intended, since the qualityrequirements for top standard roads, railway trackbed and concrete materials differ quite widely.Consideration of these aspects is of great environmental importance. The immediate classification of bedrockwhen the intended use of the extracted material is already known, renders reloading unnecessary and this too

is of considerable economical importance.

INTRODUCTION

Environmental geology concerns the intersection between geology, i.e. bedrock, Quaternary deposits,groundwater, and also human activity. Geology is influenced by natural processes like volcanism,earthquakes, flooding, landslides, etc., and extensive human impact (cf. Selinus, 1996; National Atlas ofSweden, 1994). There is an increasing demand for environmental approaches in society at large and a greatneed for the presentation of applied geology in particular. This has also led to interactionandcollaborationbetween geology, engineering geology, geotechnics and civil engineering. As examples ofthematic maps produced by SGU can be mentioned: maps for municipal planning including protection ofgroundwater (vulnerability), permeability, vulnerability to acidification, conflicting requirements (gravel

1 Lars Persson, Geological Survey of Sweden, SGU, Box 670, SE-751 28 Uppsala, SWEDEN. [email protected]


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deposits, nature conservation, groundwater), radon prognosis, erosion risk (landslide), soil geochemistry,heavy metals in drainage and sewerage systems (biogeochemistry), and bedrock quality (cf. Selinus, 1996).Integration of these information sheets is highly desirable, as this would lead to increased knowledge. 3Dtreatment of all these data stored in databases is inevitable. Large-scale infrastructure schemes (includingunderground works) in densely populated, urban areas increase the need for and importance of suchinvestigations even more. This makes the interaction between geology and engineering geology substantial,especially regarding the excavation of tunnels and caverns, i.e. underground planning in a wider sense (cf.Morfeldt, 1993; Morfeldt and Persson, 1997; Persson, 1998d).

PROJECTSIN THE DENSELY POPULATED PARTS OF SWEDEN

Originally 15- later 12- densely populated areas wereselected by SGU to be covered by geoscientificinvestigation. Densely populated areas correspond to regionshaving within a radius of 30 km, or a municipality (kommun)with at least 100,000 inhabitants. The main areas of activityare: bedrock geology, bedrock quality, the geology of

Quaternary deposits, groundwater geology, geophysics,geochemistry and marine geology. The scale used in theseprojects is 1:50,000. From the outset (A.D. 2000),investigations are being concentrated on Swedens threemain populated areas: Lake Mlaren including Stockholm,the Gothenburg area on the west coast, and the resund areaincluding Malm and Helsingborg (facing Denmark, Figure1). The projects achievements will vary, due to the fact thatthe geological conditions are so different. An important wayforward is to integrate information in order to create otherthematic maps. These will be important tools for the plannersto use, all for the ultimate benefit of the population.

Figure 1: Map of Scandinavia and Finland and the locationsof Stockholm, Gothenburg and Malmoe.

Lake Mlaren project

This SGU project, commencing this year, involves major the towns Vsters, Eskilstuna, Enkping,Uppsala, Sdertlje, Strngns and Stockholm. Inititally five municipalities are being investigated in thewestern part of the Lake Mlaren region, viz., Vsters, Eskilstuna, Hallstahammar, Kping and Kungsr.

Here, investigations of bedrock, bedrock quality, groundwater, geochemistry, radon and marine geology arebeing performed. Cooperation with the users of the information is already established. Aerial geophysics andthe investigation of Quaternary deposits are already completed and are to be compiled. Geophysicalmeasurements of gamma radiation are being performed on site when the aerial results show anomalousvalues. Marine geology involves environmental geochemical sampling, investigations of sub-aquatic glacialdeposits (contiguous with subterranean deposits), of areas of sedimentation and erosion, and also of the baseof fine and coarse sediments and rocky outcrops. Urban geochemistry is performed to determineconcentrations of metals in relation to the natural geological background. Biogeochemical investigations arealso urgently needed to show how elements in the environment are used and discharged by organisms. Forinstance, roots of aquatic plants are being analysed (cf. Selinus, 1996; National Atlas of Sweden, 1994).

Stockholm

SWEDEN

FINLAND

DENMARK

NORWAY


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APPLIED BEDROCK GEOLOGY

Bedrock geology and bedrock quality

A new series of thematic maps, the bedrock quality maps, complementary to the regular bedrock maps ona scale of 1:50,000, is being produced by SGU (cf. Persson, 1998a; b; c; Persson et al., 1998a; b; c). Themethodology of this work has been elablorated in cooperation with the Swedish National Testing andResearch Institute, SP (cf. Persson and Schouenborg, 1995; 1996). The main purpose of the maps is tofacilitate the evaluation of the best use of different rock types as, for example, aggregates for roadconstruction (pavement) and railway trackbed and for the production of concrete. They will also beinvaluable for the planning of aggregate resources and for infractructural works, also underground(tunnelling, etc.). These maps will shortly cover the Stockholm and Lake Mlaren region and themunicipality of Gothenburg, followed by other densely populated areas. The reason for these investments iscurrent infrastructural work (cf. Persson, 1998e; Underground Construction, 1999).

A field check of the main rock units is made, usually in at least 50 localities per map-sheet (625 km2).Thin sections and petrographic analyses are produced from each locality. The orientation of joints and sets of

joints is measured, and jointing is estimated (number of joints per metre). An interpretation of lineaments ismade, for which the height database on the scale of 1:50,000 is used. Lineaments are also interpreted from

anomalies in the magnetic and electromagnetic (VLF) surveys. The VLF map shows electrically conductivehorizons in bedrock, e.g. water- or graphite-bearing zones. These are weakness zones in bedrock. Electricalconductive minerals such as graphite should not be used for railway trackbed. The bedrock quality mapsshow structural trends of schistosities and also potential weakness zones in bedrock along which the rockfalls apart when extracted. Radiation is measured in each locality and on different rock types. Ascintillometer and a spectrometer are used to measure U, Th and K and the overall gamma radiation inoutcrops. From this information the radium index is calculated; it is recommended not to exceed a value of 1(kerblom et al., 1990; BFS, 1990).

Rock material is taken from quarries and blasted road-cuts, and if possible from tunnel construction sites.Going as one proceeds downwards in bedrock, the quality of the rock material usually improves. Thematerial is crushed, first in a rotary crusher and then in a laboratory jaw crusher. This multicrushing makesthe material more cubic. Nordic tests for studded tyres are performed. The analysed fraction is 11.216 mm.

This is a mainly abrasive test, comparable to the Microdeval method. Los Angeles (LA) tests are also made.The rock is crushed and screened to obtain a comparable particle shape with a flakiness index (Swedish) inthe range of 1.30 and 1.40. Then the LA values are determined, using an analysed fraction of 1014 mm,according to the European standard, EN 1097-2. Point load indexes have in some cases been performed. Thinsections of all rock types have been studied regarding aspects of alkali silica reactivity, ASR (cf. Lagerbladand Trgrdh, 1992; West 1996). Grain size and grain boundaries are studied in detail. It is also important tostudy the decay of minerals. Owing to their high sulphide content, some rock materials should be tested

before being used for concrete. Sulphides tend to discolour the concrete and also cause pop-outs. For thefuture, the use of analytical methods such as Polished Stone values (PSV), Uniaxial Compressive Strength(UCS) and ultrasonic tests is being discussed. The differences that can arise concerning strength when rocksare tested under different conditions are demonstrated by Hawkins (1998).

Rock samples have been classified for three purposes: roads construction (mainly wearing courses),

railway trackbed construction, and concrete (cf. Persson and Schouenborg, 1995; 1996). The classification ofthe rock material for roads (pavements) is based on the requirements of the Swedish National RoadAdministration. Here the classification into three classes is based mainly on the studded tyre test (abrasion),

petrographic analysis, and brittleness (LA values). The use of aggregate as railway ballast is restricted to twogeneral classes, good and poor. Relevant parameters are petrographic composition, mainly the quartz andmica content, water absorption and the LA value. The requirements are laid down by the Swedish NationalRailway Administration. Quality for concrete classification is in three grades: petrographic analysis, mineralcomposition, grain size, grain boundaries, structure, porosity, the degree of weathering and the presence ofsulphides and alkali-silica reactive material, here mainly highly deformed quartz. Radiation measurementsare performed and the radium index is calculated. Areas designated class 1 (good), class 2 (average) andclass 3 (less suitable) are shown on the maps. The results of the other technical analyses have been evaluatedand integrated, as also is geophysical information. It should be emphasized that detailed investigations(prospecting and planning) must be performed before the excavation of rock material may be started (cf.Primel, 1977).


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Presentation of information

The symbols used for presentation are national. Although it would be desirable to apply a European oruniversal system, this is difficult owing to varying geological conditions. Nevertheless, it is important thatuseful, consistent symbols are used which can be readily understood by the users of such information. Thesymbols dealing with underground works follow the classification system compiled by the Swedish Societyof Engineering Geology and Swedish Society of Geotechnics. A standard key is established at GeologicalSurvey of Sweden (SGU), for all computer-based maps.

Several different scales may be used, depending on the purpose of an investigation. Investigatorsdependent on their activities, e.g. state governmental authorities, private enterpreneurs, and researchers, usedifferent scales. Regional investigations use such scales as 1:25,000, 1:50,000 and 1:100,000. Prospectingrequires scales like 1:5,000 and 1:10,000, while site investigations must be even more detailed. Nowadaysmost information is stored in digital form (cf. Bobrowsky et al., 1995; Edwards, 1996) and can be plottedeasily. The way of presenting information on maps is crucial for their users. In this way, the development ofthematic maps and presentations has expanded (cf. Jnawali and Tuladhar, 1999). Different ways of doing thishave evolved. Presentation of the information in 3D and 4D form is very effective, thanks to computertechnology (cf. Morfeldt and Persson, 1997; Persson, 1998d). 3D presentations of geological and engineering

geological information for underground sites have been developed at SGU (M. Strng, SGU, pers.comm).Such models are also effective in the prospecting phase or later, during excavation. Using subsurfaceoccurrences, rock can be classified with regard to quality during excavation in order to avoid reloading.Different types of investigations are usually performed to identify the aggregate resources. These inventorieshave been made to assess the prospects of using the resources in the best possible way and what qualities andresources exist (cf. Lindn, 1990; Neeb, 1992; Smith and Collis, 1993; Baker, 1996; Bobrowsky, 1996).

Experiences of bedrock quality investigations

The investigations have now been proceeding in Sweden for some years. So far a surface of 3,750 km2

has been covered and during this year (2000) another 3,125 km2 will be added. There is a growing interestand demand for these maps and databases. When an entire region, such as Lake Mlaren has been completed,the use of rock resources and the opening of quarries is greatly facilitated.

So far, analysis of about 500 samples has given us a considerable knowledge of the different rock types,their properties, and the variations among them (cf. Persson 1998,e). The Lake Mlaren region comprisescrystalline Precambrian rocks, 1.9 to 1.7 Ga old. Sedimentary veined gneisses predominate and vary incomposition, especially regarding mica content. Amphibolites are intercalated. Gneissic granitoids arecommon, varying compositionally from granite to granodiorite and tonalite. Greenstones (amphibolites andgabbros) and younger granites are present. The veined gneisses vary widely in quality, due mostly to theirmica content but also to grain-size. Even so, some rock types have low studded tyre test values, especiallyquartz and feldspar-rich varieties, the so-called greywackes. The occurrence of sulphides and graphite inthese rock types must be considered. The gneissic granitoids also vary in quality, concerning both LA valuesand studded tyre test values. The dark minerals of the tonalites, such as the basic rocks, make them less

brittle, compared with granites. It is also known that polished stone values (PSV) of basic rocks may be goodin spite of high studded tyre test values (Hbeda, 1999). This is important as the use of studded tyres during

the long winters in Sweden has increased the usage of hard, fine-grained, quartz-rich rock. The change-overto friction tyres and light-weight studs has reduced the wear on road surfaces, giving an increased polish asresult. Thus the effect of polishing is nowadays clearly evident (cf. Hbeda, 1999). The younger granites,

previously used as building stone, show very good (low) studded tyre test values, especially when fine-grained, but are generally rather brittle. The minerals can be more or less transformed. The problem ofweathering is usually not very great in Sweden, though sufficiently important to warrant consideration (cf.Carroll, 1970; Tugrul and Gurpinar, 1997).

It is really very important to know the planned use of stone before excavation is started, as the propertiesof rock vary widely. It is not possible to open quarries in rock types very good for all purposes. Moreover, a

particular rock type can have different properties in different regions, owing to geological evolution, such aslarge-scale deformation and metamorphism. That is why it is necessary to investigate bedrock as early as

possible and definitively before the prospecting and exploitation of rock starts. All stockpiling and reloadingof material should be avoided. The commercial demand for high quality aggregates and consideration of theenvironment require thorough bedrock investigations.


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ACKNOWLEDGEMENTS

The author thanks Mattias Gransson and Olle Selinus, SGU, for constructive criticism, and Max Brandt,Uppsala for reviewing the English text.

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