Strength and Deformation Properties of Volcanic Rocks in Iceland

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Strength and deformation properties of volcanic rocks in Iceland

Foged, Niels Nielsen; Andreassen, Katrine Alling

Published in: Proceedings of the 17th Nordic Geotechnical Meeting

Publication date: 2016

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Citation (APA): Foged, N. N., & Andreassen, K. A. (2016). Strength and deformation properties of volcanic rocks in Iceland. In Proceedings of the 17th Nordic Geotechnical Meeting

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Volcanic rocks ‒ Strength and deformation properties of volcanic rocks in Iceland

Strength and deformation properties of volcanic rocks in Iceland

N. N. Foged Department of Civil Engineering, Technical University of Denmark, [email protected]

K. A. Andreassen Department of Civil Engineering, Technical University of Denmark, [email protected]

ABSTRACT Tunnelling work and preinvestigations for road traces require knowledge of the strength and deformation properties of the rock material involved. This paper presents results related to tunnelling for Icelandic water power plants and road tunnels from a number of regions in Iceland. The volcanic rock from Iceland has been the topic for rock mechanical studies carried out by Ice- landic guest students at the Department of Civil Engineering at the Technical University of Den- mark over a number of years in cooperation with University of Iceland, Vegagerðin (The Icelandic Road Directorate) and Landsvirkjun (The National Power Company of Iceland). These projects involve engineering geological properties of volcanic rock in Iceland, rock mechanical testing and parameter evaluation. Upscaling to rock mass properties and modelling using Q- or GSI-methods have been studied by the students and are available in their MSc-theses, but will not be covered here. The present contribution gives a short engineering geological overview of the volcanic rock formations in Iceland. Furthermore, the results of a number of unconfined, Brazilian, and a limited number of triaxial compression tests are presented and evaluated. The results are grouped according to engineering geological classification and classification properties such as bulk density. Correlations between the bulk density and the logarithm to the elasticity modulus and strength parameters are established and discussed.

Keywords: Volcanic rocks, Iceland, UCS test, Brazilian test, elasticity modulus.

these to rock mass parameters which then 1. INTRODUCTION have been used for numerical analysis using international methods like GSI, RMR and Q- This paper presents extracts from a number methods for stability, stand-up time and nec- of MSc-theses in Rock Mechanics carried out essary support, i.e. shotcrete thickness and by Icelandic students at the Technical Uni- rock bolt spacing. These evaluations are not versity of Denmark (DTU) in cooperation covered in any detail in this contribution but with University of Iceland, Icelandic Engi- can be retrieved from DTU. neering Companies and Vegagerðin and During the projects valuable support and data Landsvirkjun representing the Icelandic Road from the engineering investigations have Directorate and Power Administration. been provided from our cooperation partners, Most of these studies have been related to and the student reports are in full handed ongoing tunneling projects and include engi- over to these authorities when the MSc- neering geology, description of selected cores theses have been defended. This paper pre- from representative boreholes, laboratory sents selected results of the rock mechanical classification, and strength and deformation testing and gives an overview on basic classi- tests. Based on this the students have evalu- fication properties covering different Iceland- ated element properties of the actual volcanic ic rock types. The studied projects cover sites rock types and established an upscaling of from several regions of Iceland.

1 Volcanic rocks ‒ Strength and deformation properties of volcanic rocks in Iceland

2. SHORT GEOLOGICAL OVERVIEW ternary period (The Grey Basalt Formation and the Móberg formation). Iceland is situated on the Mid-Atlantic ridge Figure 1 is extracted from the monograph by on the rifting plate boundary between the Thorleifur Einarsson: “Geology of Iceland. Eurasian and North American plates. When Rocks and Landscape” (Figure 24-2; Page the plates drift apart, the gap between them 233) and edited to include the localization of fills constantly with extrusive and intrusive the different tunnel sites discussed. The Ice- igneous rock. The active zone of rifting and landic bedrock consist of primary numerous, volcanism is found across the country from extensive but relatively thin basaltic lava the southwest Reykjanes peninsula to the flows, lying on top of each other, interbedded northeast where it connects with the Iceland- with subordinate acidic rock and relatively Jan Mayen ridge. Iceland is geologically very thin sedimentary beds. The bedrock’s overall young and all bedrock was formed within the composition is as follows: past 25 million years. The stratigraphical • 80–85% basalt lava flows, succession of Iceland covers two geological • 10% acidic and intermediate rocks, periods, the Tertiary and the Quaternary. The • 5–10% sedimentary interbeds originating oldest rocks observed at the surface are about from both erosion and transport of vol- 15 million years old, and are from late Ter- canic rocks. Mainly consolidated tuff and tiary time. They are found in the Northwest eolian soil and to some extent sandstones and Eastern coast of Iceland. The rock closer and conglomerates. to the rifting plate boundary is younger. Each lava flow may be divided into three The surface of Iceland has changed radically parts as follows: with time. The rocks are weathered by the • The top scoria, often 10–25 % of the lava frequent change of the frost and thaw, and the flow thickness, wind, seas and glaciers erode down the land. • The dense crystalline middle part, often

60–85 % of the lava flow thickness, • The bottom scoria, often 5–10 % of the lava flow thickness. The top scoria is to the uppermost portion of a lava flow, characterized by rapid cooling and expansion of gas. The matrix of scoria is highly vesicular and glassy. The structure is chaotic, with large voids of any size, some up to several meters. When the subsequent dep- osition of sediment occurred, these voids were infiltrated and filled with sand and silt. Palagonitisation later cemented the sediment into a sandstone or siltstone and gives the Figure 1 Extent of the Islandic geological for- rock mass a relatively compact aspect. In mations. Bedrock: 1) Tertiary Basalt Formation; cores the top scoria often has character of a 2) Grey Basalt Formation, Late Pliocene and matrix supported breccia with scoria frag- Early Pleistocene; 3) Móberg (eng. Hyaloclas- ments. The vesicles in the scoriaceous frag- tite) Formation, Late Pleistocene. Site locations: ments are also often filled with secondary Olafsfjörður (O), Núpur and Þórsá (T), zeolites or calcite. The scoria can be recog- Kárahnjúkar (K), Fáskrúðsfjörður (F) and Búðarhálsvirkjun (B). Based on Map from nized from its specific structure and because Einarsson (1994). of its red, orange and green colour, which contrast the grey colour of the basalts. The studied sites are placed in regions being The crystalline middle lava consists of hard, representative for the Tertiary Basalt For- dense basalt of light to dark grey colour. The mation and volcanic features from the Qua- rock is usually affected by subvertical columnar jointing, resulting from the cooling of the lava. The frequency of the joints is low 2 Volcanic rocks ‒ Strength and deformation properties of volcanic rocks in Iceland for these large columnar jointed basalts with Table 1 Icelandic basalt classified according to spacing between 1–2 m. Correspondingly the rock engineering properties, Jónsson (1996). frequency is high for small columnar jointed Field Proposed geo- Structural and mechanical basalts and between 0.1– 0.3 m, showing a mapping technical field properties sugarcube structure. The joint surfaces are of Iceland- mapping of Scoria Common Common ic basalts1 basalt content thichness UCS usually smooth to slightly rough, undulating (%) of lava strength2 with gauge absent or only with thin clayey unit (m) (MPa) coatings or calcites. Tholeiite Tholeiite, thin >200 The bottom scoria is commonly observed to basalt layered (from 25–35 3–8 central volcanoes) (150‒300) be thin, well consolidated, sometimes con- Tholeiite, thick, >200 taining sandstone fillings, originating from 15–20 10–20 regional (150‒300) underlying sediments. Porphyritic Porphyritic basalt basalt esp. massive. 200 The basalt is classified according to Walker’s 1–5 10–20 Phenocrysts>10% (100‒300) classification system based on petrology and by volume texture of the rock and is divided into the Porphyritic basalt. following three different petrographic types Phenocrysts < 10% by volume 200 5–15 10–20 (Walker, 1959): (150‒300) • Olivine Olivine basalt Tholeiite basalt, tholeiite • Olivine basalt, Compound lavas, • from lava shield 0–5 20–80 100 Porphyritic basalt. (80‒140) Table 1 gives a number of rock engineering volcanoes 1According to Walker (1959) properties of which UCS for fresh basalts 2 Fresh basalt show relatively high strengths (Jónsson, 1996).

3. ROCK MECHANICAL TESTS AND EVALUATION

All test specimens were cut from the available cores (or recored) to the wanted dimen- sions H and D measured by a caliper. The cutting was done using a water-cooled dia- mond saw. Afterwards the test specimens were water saturated under vacuum in order to determine the water-saturated bulk density in surface dry condition. This property was used as abscissa in the preceding figures A B showing the obtained strength parameters σt and σc and elasticity moduli E as ordinates on logarithmic scale. When performing rock mechanical surveys the traditional tests are unconfined uniaxial compression tests (UCS) and Brazilian tests. The Brazilian tests are performed according to the ISRM standard for determining indirect tensile strength of rock materials (Bieniawski & Hawkes, 1978), and the setup is as seen in Figure 2 (C). The C purpose of the uniaxial compressive tests is to measure the uniaxial compressive strength Figure 2 Test setup overview with specimens and to determine stress-strain curves for equipped for strain measurements. (A) Triax- Young’s modulus E and Poisson’s ratio υ. ial test. (B) UCS test. (C) Brazilian test.

3 Volcanic rocks ‒ Strength and deformation properties of volcanic rocks in Iceland

Figure 2 (A) and (B) illustrate the different (MPa) is the Brazilian strength. This proce- deformation measuring methods: Strain clips dure requires that the material is isotropic and and strain belts, LVDT’s and strain gauges that both the extensional and compressional glued upon the test specimen cylindrical sur- failure can be described by the Mohr- face. Most of the E-moduli have been deter- Coulomb failure criteria, which is not always mined as E* using LDVT’s which include the case (Ramsay & Chester, 2004; Labuz & bedding effects at end platens in the com- Zang, 2015). pression machine and we have found the ratio E/E* = 1.80±0.57 in comparison to strain 4. ROCK MECHANICAL PROPERTIES gauges measurements. EXTRACTED FROM MSC-THESES The uniaxial compressive tests are performed according to the ISRM standard for determin- 4.1 Gudmundur Nikulasson (1987): “Tun- ing the uniaxial compressive strength neler i vulkanske bjergarter i Island” (Bieniawski et al., 1979). More advanced test This MSc-thesis was carried out based on schemes have comprised triaxial tests in the project investigations in cooperation with DTU MTS-815 rock testing facility accord- Vegagerðin Rikisins – the Icelandic Road ing to the ISRM standard for determining the Directorate – for a road tunnel at Olafsfjör- strength of rock materials in triaxial com- ður Muli in Northern Iceland established pression (ISRM 1983). The triaxial tests are 1988–1990. performed for obtaining the strength at higher Rock samples from the Tertiary Basalt For- confining pressures to determine the friction mation were selected from boreholes OM1-4 angle, φ (°), and the cohesion, c. under guidance of Hrein Haraldsson and In the cases where triaxial tests are not per- Gunner Bjarnason from. Five different basalt formed it is possible to use the procedure types were selected (Porphyritic B1, Olivin described by Madland et al. (2002) to com- B2, Olivinporphyritic B3, Tholeiite B4 and bine UCS and Brazilian test results and de- Tholeiiteporphyritic B5) together with Scoria termine the friction angle by: and sedimentary samples, all from the Ter-

/ tiary Basalt Formation. sin = = / , (1) The rock mechanical testing by the student at 𝜎𝜎𝑐𝑐−4𝜎𝜎𝑡𝑡 𝜎𝜎𝑐𝑐 𝜎𝜎𝑡𝑡−4 the Rock Mechanical Laboratory at the Dan- 𝜑𝜑 𝜎𝜎𝑐𝑐−2𝜎𝜎𝑡𝑡 𝜎𝜎𝑐𝑐 𝜎𝜎𝑡𝑡−2 where (MPa) is the UCS strength and ish Geotechnical Institute involved classifica-

𝑐𝑐 𝑡𝑡 100000𝜎𝜎 𝜎𝜎 = 14 . 2 6𝑥𝑥 10000 𝑦𝑦 𝑒𝑒

1000

= 0.045 . 100 2 6𝑥𝑥 𝑦𝑦 𝑒𝑒 (MPa)

. , E = 0.0045 c 10

σ 2 6𝑥𝑥 , t 𝑦𝑦 𝑒𝑒 σ

0,1 1,25 1,50 1,75 2,00 2,25 2,50 2,75 3,00 Bulk density (g/cm3)

Figure 3 Rock mechanical test results from Olafsfjörður Muli (Nikulasson, 1987).

4 Volcanic rocks ‒ Strength and deformation properties of volcanic rocks in Iceland tion tests, 86 point load tests, 51 Brazilian around the mountain Núpur and the river tests (for σt) and 41 unconfined compression Þórsá is various and complicated including tests (for σc). the 8700 years old Þórsá lava being the most In the later 10 tests were performed used significant rock layer in the area. It overlies strain gauge techniques for Young’s E- sedimentary layers, e.g. silt-and sandstone, modulus and Poisson’s ratio ν and the rest volcanic sand and conglomerate being 1.64 using external LDVT’s for determination of million years old. only E*. The index * indicates bedding effect For the present project 12 different volcanic included at end platens and a ratio E/E* = and sedimentary rock types were selected 1.80±0.57 was found. from 12 boreholes in the area which contrib- Figure 2 shows the main results of the uted to 48 test specimens used for 82 Brazili- strength and deformation properties correlat- an tests, 46 unconfined compression tests and ed with the bulk density determined on water 5 triaxial tests. The results in form of σt, σc saturated surface dry test specimens. and E with different signatures for the studied rock types are plotted as function of the bulk 4.2 Karen Kristjana Ernstdottir (2003): density in water saturated surface dry condi- “Rock mechanical studies for a hydroe- tion being saturated as part of the preparation lectric power station–Near Núpur and of the test specimens. Figure 3 shows the Þórsá, Iceland” main results grouped in selected rock types This MSc-study was carried out in coopera- together with a regression analysis of the tion with Landsvirkjun and Almenna Con- trendlines for the 3 set of results with great sulting Ltd. with Björn Stefánsson and Jón variation depending on bulk density and low- Skulason as contacts. The project investiga- est values for the Móberg formations. The 5 tions related to preliminary plans for a hydro- triaxial tests confirm the high level of friction electric powerstation at Núpur and included angle and cohesion for Tillite, Porphyritic 12 km headrace tunnels. The main subject of Basalt, and Hyaloclastic as evaluated in Sec- this project was to obtain rock parameters for tion 5. the different rocks in the region based on laboratory tests on rock samples from drilling cores made available. The geology in the area

100000 = 26 . 2 6𝑥𝑥 𝑦𝑦 𝑒𝑒 10000

1000

= 0.052 .

(MPa) 100 2 6𝑥𝑥 𝑦𝑦 𝑒𝑒 , E c σ . ,

t = 0.0052 10 σ 2 6𝑥𝑥 𝑦𝑦 𝑒𝑒

0,1 1,25 1,50 1,75 2,00 2,25 2,50 2,75 3,00 Bulk Density (g/cm3) Figure 4 Rock mechanical properties from volcanic rock types in the Núpur – Þórsá region (Ernstdottir, 2003).

5 Volcanic rocks ‒ Strength and deformation properties of volcanic rocks in Iceland

4.3 Hlif Isaksdottir (2004): “Rock mechanical equipment at DTU showed in combina- cal studies of volcanic tephra for a hy- tion with the Brazil tests for ρbulk = 2.02 droelectric power station–Near Núpur g/cm3 high friction angle of φ = 55.4o and c = and Þórsá, Iceland” 1.35 MPa for the cemented sandstone. This MSc project was carried out on one of the largest tephra layers found below the 4.3 Gunnar Arnar Gunnarsson (2008): Þórsá Lava with varying thickness from a “Rock Mass Characterisation and Rein- few to about 30 m and properties ranging forcement Strategies for Tunnels in Ice- from slightly cemented sand to sandstone. land, Fáskrúðsfjörður Tunnel.” The layer is a result of a sub-glacial volcanic This MSc-thesis was worked out in coopera- activity 10300 years ago followed by an out- tion with the University of Iceland, Faculty burst flood. From this tephra layer three dif- of Civil and Environmental Engineering ferent types of samples were available: Two (Sigurður Erlingsson) and GeoTek Ltd. block samples of variably cemented sand and (Oddur Sigurðsson) and Vegagerðin – the a sandstone core from borehole NK-28. Gen- Islandic Road Administration. Hallgrimur erally, RQD and Q-index are very low (0–3% Örn Arngrimsson (a fellow student) partici- and 0 respectively with exemption of the core pated at GEO (The Danish Geotechnical In- from NK-28 having RQD = 88 and Q = 3– stitute) and DTU in the rock cores classifica- 46). The tephra particles have a vesicular tion and preparation of test specimens and the nature with air trapped inside the grains, actual laboratory testing. weathering may change density due to when The project investigation for this site being volcanic glass alters to palagonite. Four and established 2003‒2005 was used and twelve two subsamples from the two buckets of rock cores were collected for supplementary tephra showed low saturated bulk density of testing mainly of scoria and sediments. A 3 3 1.74 g/cm to 1.79 g/cm and wsat from 43% large laboratory test dataset from the head- to 39% compared to natural water contents race tunnel in the Kárahnjúkar hydroelectric wnat from 13% to 12.5%. Deformation prop- project was analysed for comparison of erties in consolidation test on the tephra strength properties for the Fáskrúðsfjörður showed very low Eoed-moduli and conse- tunnel having a geological age of about 6.5 quently the material may be vulnerable to and 10 mill years, respectively. Consequent- creep and to additional settlements under ly, focus has been on scoria or porous basalts dynamic loads. The tephra sands in Bucket 1 and sediments in the present case. Gunnar and 2 were very friable and could not be or- used a comparison method applied on lime- derly used for Brazilian tests in saturated stone from the construction of the Citytunnel condition. However, at natural water content in Malmö (Foged et al., 2004) based on the the partially saturated test specimens showed semilogarithmic plot of tensile strength, un- σt ≈ 0.28 MPa and 0.025 MPa, respectively. confined compression strength and Young’s Properly conducted tensile strength tests on modulus versus bulk density for the different six cemented subsamples from the cores from rock types. The comparison is available in NK-28 with saturated bulk density of ρbulk = Figure 5 and Figure 6 and the reduced rock 3 2.01 g/cm showed a mean value of σt = 0.69 mechanical properties at Fáskrúðsfjörður MPa. Four triaxial tests and one unconfined compared to Kárahnjúkar is discussed to be compression test on test specimens from NK- due to different age, weathering and high 28 carried out in the MTS 815 rock mechani- stress conditions.

6 Volcanic rocks ‒ Strength and deformation properties of volcanic rocks in Iceland

100000 = 10 . 2 6𝑥𝑥 10000 𝑦𝑦 𝑒𝑒

1000

100 . (MPa) = 0.020

, E 2 6𝑥𝑥 c

σ 𝑦𝑦 𝑒𝑒

, 10 t . σ = 0.0020 2 6𝑥𝑥 𝑦𝑦 𝑒𝑒 1

0,1 1,25 1,50 1,75 2,00 2,25 2,50 2,75 3,00 Bulk density (g/cm3) Figure 5 Rock mechanical properties for the Fáskrúðsfjörður region (Gunnarsson, 2008).

1000000

100000 = 14 . 2 6𝑥𝑥 10000 𝑦𝑦 𝑒𝑒

1000

= 0.075 . 100 2 6𝑥𝑥 𝑦𝑦 𝑒𝑒 (MPa) .

, E = 0.0075 c 2 6𝑥𝑥

σ 10

, t 𝑦𝑦 𝑒𝑒 σ

0,1 1,25 1,50 1,75 2,00 2,25 2,50 2,75 3,00

Bulk density (g/cm3) Figure 6 Rock mechanical properties for the Kárahnjúkar region (Gunnarsson, 2008). Data received from the Kárahnjúkar hydroelectric project.

(Matthias Loftsson and Jón H. Steingrims- son) and was in part funded by the Icelandic 4.4 Hallgrimur Ôrn Arngrímsson & Þorri Road Administration (Vegagerðin). The fo- Björn Gunnarsson (2009): “Tunneling in cus of this thesis is tunnelling in soft rock acidic, altered and sedimentary rock in formations like acidic, altered and sedimen- Iceland, Búdarhálsvirkjun” tary rock. The top part of Búðarháls for- This MSc project was performed in coopera- mation is pillow lava generated by subglacial tion with the University of Iceland, Faculty eruption during the last glacial period (hyalo- of Civil and Environmental Engineering clastic rock approx. 0.7 million years old). (Sigurður Erlingsson) and Landsvirkjun 7 Volcanic rocks ‒ Strength and deformation properties of volcanic rocks in Iceland

100000 = 16 . 2 6𝑥𝑥 10000 𝑦𝑦 𝑒𝑒

1000

y=0.055e2.6x 100

2.6x E (MPa) 10 y=0.0055e , c σ , t σ 1

0,1 1,25 1,50 1,75 2,00 2,25 2,50 2,75 3,00

Bulk density (g/cm3)

Figure 7 Rock mechanical properties for the Búðarháls region (Arngrímsson & Gunnarsson, 2009).

A/B = 10 gives a first order estimate for the It is underlain by multiple basaltic lava flows friction angle mechanical testing. Core samples were col- / lected on eight different rock types which = sin = sin (0.75) = 49 / , (2) were used for Brazilian, unconfined com- −1 𝜎𝜎𝑐𝑐 𝜎𝜎𝑡𝑡−4 −1 ∘ pression and triaxial compression tests per- 𝜑𝜑 �𝜎𝜎𝑐𝑐 𝜎𝜎𝑡𝑡−2� for most volcanic rock types. formed at Geo and DTU. The Geological

Strength Index GSI was used to estimate rock Table 2 Parameter evaluation for the five sites mass properties analysed in three different presented in Section 3 taking into account that tunnel cross-sections using the finite element the exponential factor in the regression equations 2 program Phase and the designed rock sup- is equal as listed here: σc = A exp(2.6 ρb), σt = B port classes recommended in the contract exp(2.6 ρb) and E = C exp(2.6 ρb). documents (Arngrímsson et al., 2010). Coefficients for: 5. EVALUATION AND CONCLUSION σc σt E Locality Type A B C A/B C/A Olafsfjör- Tertiary 0.045 0.0045 14 10 311 The trends established for compression ður Basalt strength, tensional strength and elasticity Early Pleisto- Nupur modulus must be taken with some caution. cene/ 0.052 0.0052 26 10 500 Þórsá The different rock types included and the Þórsá Lava local variability should be included in an Early Kárahn- Pleisto- overall evaluation. 0.075 0.0075 14 10 187 júkar * cene However, the main finding that an exponen- Moberg tial factor of 2.6 in the regression equations Fáskrúðs- Tertiary 0.020 0.0020 10 10 500 fit all the different plots from sites in differ- fjörður Basalt Early ent geological type formations seem to be Pleisto- Búðarháls cene/ well defined. Consequently, using the 0.055 0.0055 16 10 290 virkjun Móberg Madland method discussed in Section 4 for and the unconfined compression strength and the Rhyolite in-direct tensile strength, the ratio for σ /σ = * C/A influenced by low density or porous rock types. c t

8 Volcanic rocks ‒ Strength and deformation properties of volcanic rocks in Iceland

A lower bound value may be A/B ≈ 8, i.e. 6. ACKNOWLEDGEMENTS = 41°. As the friction angle φ is difficult and costly to determine using triaxial tests on We thank the six Icelandic guest students at such𝜑𝜑 rock formations this makes evaluations the Department of Civil Engineering, Tech- of strength parameters simpler taking into nical University of Denmark for their dedi- account that the internal cohesion c may be cated work during the period of 1987‒2009. estimated from (Madland et al., 2002); The cooperation with and support from Uni- versity of Iceland, Vegagerðin and Lands- = 3 . (3) virkjun, and from Icelandic Engineering Companies are highly appreciated. Further- 𝑡𝑡 more, the Rock Mechanical Laboratory at The design𝑐𝑐 √ value𝜎𝜎 of σt should be carefully estimated as a lower bound value related to Geo, Denmark, has kindly provided facilities the actual rock types and their classification for sample preparation and testing. properties in form of saturated surface dry bulk density. Using the constants A, B and C summarized 7. REFERENCES in Table 2 the differences between sites are evident related to the different volcanic rock Arngrímsson, H.Ö. & Gunnarsson, T.B. (2009). Tunneling in acidic, altered and sedimentary rock in types like scoria and sand- and siltstone de- Iceland – Búdarhálsvirkjun. MSc-thesis at Department rived from tephra. Beside the influence of of Civil Engineering, Technical University of Den- porosity and variable mineralogy there seems mark. to be an effect of weathering and age of the Arngrímsson, H.Ô., Gunnarsson, T.B., Foged, volcanic formations. The Tertiary Basalt sites N.N. & Erlingsson, S. (2010). Numerical Analysis of Rock Support Strategy for the Búdarháls Tunnel. Con- show lower strength parameters than the ference on Rock Mechanics in the Nordic Countries, Þórsá Lava and especially all formations pro- Kongsberg, Norway. ne to weathering like scoria sedimentary in- Bieniawski, Z.T., Franklin, J.A., Bernede, M.J., terbeds of acidic tuffs show very variable Duffaut, P., Rummel, F., Horibe, T., Broch, E., Ro- strength and deformation properties depen- drigues, E., van Heerden, W.L., Vogler, U.W., Han- sagi, I., Szlavin, J., Brady, B.T., Deere, D.U., Hawkes, ding on their position in the basaltic succes- I. and Milovanovic, D. (1979). Suggested Methods for sions. Determining the Uniaxial Compressive Strength and Most of the determination of elasticity modu- Deformability of Rock Materials. International Journal li has been done with LVDT’s measuring the of Rock Mechanics and Mining Sciences & Geome- total deformation between end platens in the chanics Abstracts, Vol. 16, No. 2, pp. 135-140. Bieniawski, Z.T. & Hawkes, I. (1978). Suggested compression machine. As this include bed- Methods for Determining Tensile Strength of Rock ding effects the E-modulus may be underes- Materials. International Journal of Rock Mechanics timated which may explain the relative low and Mining Sciences & Geomechanics Abstracts, Vol. E/σc=187 to 500 where values of 500 to 1000 15, No.3, pp. 99-103. were expected. Einarsson, T. (1994). Geology of Iceland. Rocks and Landscape. Published by Mál og menning, Rey- In conclusion the present analysis of test re- kjavík. sults from MSc theses on well-defined for- Ernstdottir, K.K. (2003). Rock mechanical studies mations (Einarsson, 1994; Jónsson, 1996) for a hydroelectric power station – Near Núpur and including provided data from Kárahnjúkar Þórsá, Iceland. MSc-thesis at Department of Civil gives a frame for comparison with future Engineering, Technical University of Denmark. Foged, N., Hartlén, J., Jackson, P.G. & Steenfelt, rock mechanics test results. The evaluation J.S. (2004). Evaluation of Bryozoan limestone proper- principles may guide the use of established ties based on in-situ and laboratory element tests. parameters towards an upscale to field pa- Proceedings of International Conference on Site Char- rameters. acterisation ISC inPorto, Portugal 2004. Gunnarsson, G.A. (2008). Rock Mass Characteri- sation and Reinforcement Strategies for Tunnels in Iceland – Fáskrúðsfjörður Tunnel. MSc-thesis at De- partment of Civil Engineering, Technical University of Denmark.

9 Volcanic rocks ‒ Strength and deformation properties of volcanic rocks in Iceland

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