NV NORDISK VINDKRAFT AB Östersund 23-06-2011, rev 06-07-2012
Geotechnical Deskstudy for Proposed Windfarm Date 23-06-2011, rev 06-07-2012 Project number 61811144691000 JONSSON EVA TAJANI KRISTINA TAJANI DAVID GALBRAITH Project Director Project Engineer Reviewer Ramböll Sweden AB Färjemansgatan 22 831 41 Östersund Telephone +46 (0)10-615 60 00 Fax +46 (0)63-13 39 40 www.ramboll.se Project no 61811144691000 VAT registration no 556133-0506
Table of Contents 1. Introduction... 1 2. Bedrock... 2 3. Quaternary Deposits... 2 4. Groundwater Conditions... 2 5. Climate Statistics... 2 6. Geotechnical Conclusions and Recommendations... 4 6.1 Summary... 4 6.2 Proposal for Field Investigations... 4 6.3 Foundation... 5 Appendices 1. Bedrock map 2. Map of quaternary deposits 3. Wind farm map 4. Map of archaeological sites and monuments 5. Map of magnetic anomaly 6. Gamma radiation map 7. Areas of national interest 8. Satellite view 9. List of references Project no 61811144691000 Date:23-06-2011,
, 1. Introduction Ramböll Sweden AB has performed a general deskstudy of the geological conditions for the construction of a new windfarm at in Lycksele community, county of Västerbotten. The work has been carried out under commission of NV Nordisk Vindkraft. The planned farm is divided in four parts with a total footprint area of about 600 square kilometers, or 6000 hectares. is situated between Åsele and Lycksele. The purpose of this investigation is to assess the suitability of the ground for the construction of wind turbine bases and access roads. The desk study is based on information from topological and geological maps showing quaternary deposits and bedrock, as well as information from geological literature, internet, meteorological and hydrological information. A search of historical information has also been carried out on the internet. According to the Swedish National Heritage Board and its database for archaeological sites and monuments (Fornsök) there are no areas of archaeological interest within the proposed windfarm site. See Appendix 4. The geological maps show quaternary deposits at the surface but are generally more accurate and representative at depths below one metre below the surface. Limited and/or narrow areas with a certain deposit or bedrock are not shown on the geological maps. Information was obtained from the Geological Survey of Sweden (SGU) and the Swedish Meteorological and Hydrological Institute (SMHI). The available maps have not included the presence of underground cavities, surface water, seismic activity, electrical resistivity and contamination. Within the area of interest there is an area of national interest for nature conservation, namely Järnesberget, which is a part of Stöttingfjället (NRO24061) according to the County Administration Board of Västerbotten. See Appendix 7. There have not been any military, mine or industrial activities in the area A satellite view is shown in Appendix 8. 1 of 5
2. Bedrock The bedrock map at is presented in Appendix 1. The bedrock in the area of consists mainly of granite and granodiorite. Within the central and western sections of the site of interest occurs sedimentary bedrock in the form of sandstone, greywacke and shale. Diabase dikes could occur in the western section. Basic igneous rock could occur in the central part. There are no indications of high radium content locally in the bedrock. The gamma radiation map (see Appendix 6) shows that the uranium content in the upper part of the bedrock or soil layer are between 0.5 and 4 ppm eu. 3. Quaternary Deposits The quaternary deposits in the area consist mainly of till and peat. Exposed bedrock are is also common. The soil layer is very thin in several areas. The magnetic anomaly map, shown in Appendix 5, shows values of between -557 to 65 nt. The western part of the area with sedimentary bedrock the values are mostly -43 to 58 nt. The resistivity in till is in the range of 100-20000 Ωm according to resistivity tables. Quaternary deposits are presented in Appendix 2. No information about content of acid or alkali in the soil has been obtained. 4. Groundwater Conditions According to the Swedish Geological Survey the groundwater capacity of the bedrock is estimated between 600-2000 l/h The depth to groundwater from the surface is estimated to be more than 5 metres on top of the hills and less than 5 metres at lower levels. In areas with peat the depth to groundwater level could be less than one metre. 5. Climate Statistics The nearest station for weather observations is located at Kroksjö, 5 kilometers northeast of. An additional weather station is located at Lycksele, which is situated 38 km east of the proposed windfarm site. 2 of 5
Winter days Spring days Summer days Autum days Kroksjö 22 Oct 182 22 Apr 48 9 June 74 22 Aug 61 Sources: 1-2, Swedish Meteorological and Hydrological Institute (SMHI) The average temperature and precipitation data from the period of 1961 to 1990 are presented in the table below. 1961-1990 Month Average Temperature Kroksjö C Average Maximum Temperature Kroksjö C Average Minimum Temperature Kroksjö C Statistics of the number of days per season are presented for the period 1961-1990 in the table below. Precipitation, Kroksjö mm Days with temperature below zero, days Lycksele Jan -10,1-7,0-13,3 39 31 Feb -9,0-5,9-12,2 28 28 Mar -5,9-2,2-9,4 34 30 Apr -1,1 2,6-4,8 37 25 May 5,4 9,8 1,3 44 12,8 Jun 10,8 15,7 6,2 60 1,3 Jul 12,4 17,0 8,3 100 0,0 Aug 10,6 14,9 6,8 83 1,4 Sep 5,9 9,5 2,8 71 8,4 Oct 1,0 3,7-1,6 58 19 Nov -5,1-2,6-7,7 55 27 Dec -8,3-5,4-11,4 41 30 Total: 641 214 Sources: 1-2, Swedish Meteorological and Hydrological Institute (SMHI) The average temperature and rainfall has had a rising trend according to current climate change data. The precipitation is stated to be 5% higher in the year 2000 than during the period 1961-1990. The average temperature is 0,8 higher during 1991-2000 than during the period 1961-1990. The local climate in is probably much similar to that experiended at the nearest weather measurement stations at Kroksjö and Lycksele. Although the higher altitude could result in more windy weather and less snow and therefore also lower temperatures and larger proportions of frozen ground, which could lead to problems with frost heave for example. Sunlight can also affect the climate during the period of late autumn to early spring (between October and March) since the sun casts light on the peaks for a longer duration of time compared to lower altitudes. 3 of 5
6. Geotechnical Conclusions and Recommendations 6.1 Summary The geological conditions described above indicate a preliminary overview of probable foundation conditions at the site. However, further site-specific geotechnical field investigations are necessary in order to explore each site s specific condition and to enable foundation design. We recommend site visits (to each windfarm area) by an experienced geotechnical engineer, prior to any field investigations with drill rigs. Thereafter, final locations and methods of soundings/testing can be decided. 6.2 Proposal for Field Investigations All geotechnical field planning, field sampling, testing, analysis and reports should be in accordance with Euro code 7, SS-EN 1997, for geotechnical design together with the national appendices. Method of sounding, sampling and number of boreholes can be decided after the site visit, but as a general suggestion: 2 to 5 boreholes per wind turbine will be necessary. Soil Investigations Soil investigations shall be done in accordance with SGF standards. If the foundation of the turbine shall be founded in soil, both sounding and soil sampling will be necessary. The investigation shall include 1-2 holes of soil sampling where depth to soil sample and depth to assumed bedrock are measured. Every soil sample shall be analysed with respect to type of soil and frost susceptibility characteristics. A few representative samples shall be sent to an accredited laboratory for further analysis to confirm additional characteristics of the soil. Sounding in 2 to 5 boreholes shall be done in order to evaluate soil parameters. Bedrock Investigations Bedrock investigations shall be done in accordance with SGF standards. If the foundation of the turbine shall be founded in bedrock, soil/rock probing with a diamond drill bit in 2-5 holes is necessary. The number of probings depends on the degree of discontinuity in the bedrock. The Swedish Jb2 or Jb3 probing is recommended to investigate the discontinuities in the bedrock. Core rock drilling is recommended to obtain samples of bedrock for laboratory analysis. The rockcharacteristics are needed for the design of anchors and foundations. At least four core samples are recommended. Investigation of Hydrological Conditions: Groundwater level shall be measured in 7-10 boreholes in the area of the windfarm, if possible. Investigations for Access Roads: Geotechnical exploration with drill rigs are needed along planned access roads. Depending on the soil and/or bedrock levels it is recommended: approximately 4 of 5
one borehole per 100 to 300 metres. If the top layers comprise peat, simple stick sounding can be performed to estimate the depth of peat in the areas for new roads. Stick sounding stop level shall be controlled in a few points with sounding or sampling. Investigation of Resistivity: The resistivity in soil shall be measured at a few locations per windfarm. Relevant water content for the soil is necessary for proper evaluation of resistivity. Investigation of Radium Emanation: No measurement data are available concerning the site of interest. It could be of interest to perform an investigation of radium emanation. 6.3 Foundation The alternatives for foundations are either a soil covered gravity foundation or a gravity foundation that is anchored in soil or in bedrock. Gravity foundations without anchoring require a heavy foundation and most probably down to a significant depth in order to achieve stability due to wind forces. Geological maps shows limited soil depths in the actual areas. Generally, a gravity foundation anchored in bedrock is probably a more stable and economical solution in the area. A foundation in an area with fractured and/or jointed bedrock is not recommended. In that case, it would probably be better to move the wind turbine to a spot with more favourable geotechnical conditions. If an anchored structure is used, pre-stressed anchors are preferable. The anchors should be tested according to DIN 4125 (SS-EN 1537). The soil in is frost susceptible, and a minimum foundation depth of 2.3 metres is recommended. 5 of 5