A Documentation of the Eastern Suorva Dam Core Field Investigations and Thermal Modeling with Regard to Frost Action

2005:076 CIV MASTER’S THESIS

A documentation of the Eastern Suorva dam core Field investigations and thermal modeling with regard to frost action

Isabel Jantzer

MASTER OF SCIENCE PROGRAM

Luleå University of Technology Department of Civil and Environmental Engineering Division of Soil Mechanics

2005:076 CIV • ISSN: 1402 - 1617 • ISRN: LTU - EX - - 05/076 - - SE

A documentation of the Eastern Suorva dam core

Field investigations and thermal modeling with regard to frost action

Isabel Jantzer

Department of Civil and Environmental Engineering Division of Soil Mechanics Luleå University of Technology

FÖRORD

Föreliggande examensarbete är ett obligatoriskt och avslutande moment inom civilingenjörsprogrammet väg- och vattenbyggnadsteknik vid Luleå tekniska universitetet. Inom den svenska utbildningen representerar arbetet 20 poäng och omfattar 20 veckor av högskolestudier. För den tyska utbildningen, omfattar rapporten ungefär 2-3 månaders fördjupande och programavslutande studier. Examensarbetet har utförts vid avdelningen för Geoteknik på Luleå tekniska universitetet och behandlar stenfyllningsdammen i Suorva. Det innehåller en praktisk undersökning av tätkärnan i Suorva-dammen samt en teoretisk analys om hur klimat påverkar materialet i tätkärnan. Detta examensarbete har varit väldigt speciellt för mig, såväl inom studierna som personligt. Många personer har varit involverade som jag gärna skulle vilja nämna och tacka. Först och främst vill jag nämna Peter Viklander på SwedPower/Vattenfall och Sven Knutsson på avdelningen för Geoteknik på institutionen för Samhällsbyggnad, som initierade examensarbetet. Jag är glad för att ha fått möjligheten att göra detta ovanliga och spännande examensarbete och tackar för hjälpen, stödet och rådgivning som jag har fått under tiden. Ett särskild personligt tack riktas till Sven Knutsson, som förmedlade examensarbetet och alltid hade tid för frågor och diskussioner. Ett stort tack riktas till Vattenfall AB för finansering. Under sommaren jag var i Suorva träffade jag många människor som var inblandade i själva byggprocessen. Jag skulle gärna vilja rikta ett stort tack till alla som var där och hjälpte mig på många olika och varierande sätt. Det innebär allt från beskrivningar av dammen till olika moment av byggandet, praktiska saker som t.ex. att bära runt mina provlådor, diskussioner om vandringsleder i fjällen samt funderingar om samhället och själva livet. Jag lärde mig mycket där ute i vildmarken tillsammans med mycket trevlig folk. Ett personligt tack riktas först och främst till Curt, Ove och Ola. Det finns många fler att tacka, men listan skulle bli lång. Åter på Luleå tekniska universitetet analyserade jag informationen som jag hade samlat i Suorva. Under denna mörka vintertid på universitetet fick jag mycket hjälp och stöd från olika håll. Speciellt hjälpsamma var de på avdelningen för Geoteknik där jag fick många möjligheter att berätta, diskutera, och fundera. Som tidigare riktas ett speciellt tack till Bo Westerberg för stöd i alla de olika situationer som uppstod, inte bara inom geoteknik. Många har varit inblandade i detta projekt och allt där omkring. Sist men inte minst riktas ett stort tack till alla som på ett eller annat sätt bidrog längs vägen.

Luleå i februari 2005 Isabel Jantzer

i PREFACE

This master thesis is the result of a compulsory and completing element of the civil engineering program. Within the Swedish program the thesis represent 20 points which comprises 20 weeks of studies. Within the German civil engineering program, the master thesis is a report which covers 2 to 3 months of profound final studies.

This thesis was carried out at the Division of Soil Mechanics at Luleå University of Technology and deals with the embankment dam in Sourva. It contains a practical part of field studies of the core of the dam, as well as a theoretical analysis about how climate influences the material in the core.

This thesis has been very special for me, both regarding studies and personal. Many have been involved whom I would like to name and to thank.

First of all I would like to thank Peter Viklander at SwedPower/Vattenfall and Sven Knutsson at the division of Soil Mechanics who initiated this thesis. I am happy to have had the chance to work with this unusual and exciting master thesis, and I would like to express my gratitude for all help, support and advice during this work. I have to address a very special personal thank you to Professor Sven Knutsson for arranging these studies abroad and for always having time for questions and discussions. I would also like to thank Vattenfall AB for financing this thesis.

I met a lot of people who were involved in the construction process during the time I spent in Suorva. To all who have been there and for all help and support I got in so many different ways- I would like to include everything, from explanations about the embankment dam or different elements in the construction process, to practical details such as helping me carry heavy boxes containing soil samples, as well as discussions about hiking paths, about society, life, future plans. Thank you! I learned a lot during this time out there together with very special people. Thanks to Curt, Ove, Ola, and all others. I would like to write down everybody’s name, but the list would become long.

Back at the university I analysed the information I had collected in Sourva. During this dark winter time I received help from different directions and in different ways. There where many possibilities for talking, discussing, and sharing thoughts with all at the division of soil mechanics. Thanks! Once again I particularly have to name Bo Westerberg, who was always there to help in all different situations.

Many have been involved in this work and everything in connection. Last but not least thanks to all of you who contributed this thesis in one way or another!

Luleå, february 2005 Isabel Jantzer

ii SAMMANFATTNING

Detta examensarbete genomfördes för att studera om Suorvadammens tätkärna påverkas av tjälningsprocesser. Stenfyllningsdammen, som stod klar 1972, ligger norr om polcirkeln i en fjällregion som är känd för kalla vintrar och mycket blåsigt väder. Dessutom är platsen utsatt för relativt stora temperaturskillnader med förhållandevis låg årsmedeltemperatur. Efter en tidsperiod på ungefär 30 år efter färdigställandet av dammen finns misstankar om att effekten av frysning och tiningscyckler kan ha betydelse för tätkärnans funktion. Temperaturer under fryspunkten leder till frysning av jorden. När vatten fryser till is bildas islinser vinkelrätt mot värmeflödet vilket leder till tjällyftning. Is har den fysikaliska egenskapen att suga ofruset vatten mot frysfronten så att tillskottsvatten höjer vattenkvoten under tjälningsprocessen. Dessutom kan stenar lyftas upp på grund av trycket under isbildningen, och kornfördelningen i jorden kan sorteras om när jorden tinar. Resultat av cykliska tjälningprocesser kan vara att strukturen i jorden, porositeten och permeabiliteten förändras, så att vattenflödet genom dammen ökar. Funktionen av tätkärnan som hydrauliskt hinder skulle således försämras. Under de genomförda fältstudierna grävdes provgropar för att utföra undersökningnar och observationer av tätkärnan. Prov från provgroparna togs för att jämföra vattenkvoten, kornstorlekfördelning och temperaturen på olika djup i marken. Fyra provgropar i olika tvärsektioner undersöktes. I två provgropar observerades att moränen hade låg temperatur jämfört med lufttemperaturen. Särskilt en provgrop visade temperaturer som låg nära fryspunkten samt att vattenkvoten var förhållandevis hög och andelen av finkorn visades sig att vara högre än i andra delar av tätkärnan. I detta speciella fall var det tydligt att materialet hade varit fruset; eftersom en tydlig skiktning av moränen kunde observeras var tjälnivån markant. Resultaten från provtagningen visade dock inte förändringar i kornstorleksfördelning som hade förväntats och gick inte att använda som information för att kunna bedöma om och hur tätkärnan påverkats av tjälningsprocessen. På grund av informationsbrist om packningsgraden, permeabilitet samt porositeten från materialet under byggnationen saknas en utgångspunkt för jämförelse och bedömning. Skillnaden inom kornstorlekfördelningen som antagits vara markant, eftersom kornen kan ha varit utsatta för omfördelning under tiningsprocessen, kunde inte påvisas. Istället påvisades att kornstorlekfördelningen hade en stor varians i jämförelse med tidigare observationer från den nya möräntäkten och gamla anteckningar från arkivet. Termiska analyser gjorda med programmet Temp/W, som bygger på finita element metoden, visar möjliga temperaturfördelningar i dammkroppen. Analysen betraktar temperaturer och vatten-nivåer under 2002 till 2004. Baserad på en inledande beräkning av temperaturfördelningen i dammen då den utsats för en årsmedeltemperatur baserat på ett 30 års medelvärde, tillämpades och beräknades två olika situationer med olika finita element nät. De två rutnäten representerar två olika byggnadsfaser av dammens krön som förekom under fältundersökningen; dels

iii hade dammen ett vanligt damkrön och dels hade krönet tagits bort på grund av reparationer och var inte helt återställd. Samtliga beräkningar visar att frysfronten ligger på ett ansenligt djup inne i tätkärnan, med en minsta nivå just vid tätkärnans krön och en maximal nivå på ett djup av 5 m i tätkärnan. Resultaten från fältundersökningarna visade i sin tur att tjälen låg på ett djup på 0.8 m. Beräkningarna ger bara en ungefärlig bild om tjälningsprocesserna som förekommer i dammen. Vindförhållanden, till exempel, försummades helt – likaså vattennivåer, vattenströmning och snö. Dessa faktorer anses dock vara betydelsefulla för tjälningsprocessen. Det kan även vara möjligt att frysfronten är längre ner i dammkroppen så att inte bara funktionen av tätkärnan, utan också att funktionen av filtren kan ha påverkats och försämrats.

iv ABSTRACT

This MSc thesis contains a study of the core of the embankment dam in Suorva which was carried out to examine if and how the material was influenced by freezing and thawing processes. The embankment dam, which was completed in 1972 and is located north of the polar circle in a mountain region known for cold winters and severe wind conditions, is exposed to a relatively wide temperature range and a comparatively low annual mean temperature. After the time period of approximately 30 years from construction, thus, it has been presumed that freeze and thaw cycles occurred and that their effects was significant for the core, which consists of a fine- grained frost susceptible moraine. Temperatures below zero lead to frost action in soils. When water in soil changes phase to ice, ice lenses form perpendicular to the heat flow and lift the soil up. As ice imposes suction to the unfrozen water, water is moving towards the freezing front, so that the water content during freezing and thawing is increased. In addition, stones can be lifted up due to ice forces and particles are redistributed when thawing takes place. Cyclic freezing and thawing can lead to changes in soil structure, void ratio and permeability, thus increasing seepage flow. Consequently, the function of the central core as hydraulic barrier inside the embankment dam may be reduced. During field investigations test pits were excavated and visually inspected. Samples from the core of the embankment dam were collected; water content, grain-size distribution and temperature in the soil were measured. Each of the four test pits was examined at different levels of depth, and it was found in two test pits that the moraine had relatively low temperatures compared to air temperatures. Especially in one test pit the temperatures were found to be close to the freezing point, the water content was extremely high and the content of fine-grained material was increased. In this special case it was obvious that the soil had been exposed to freezing, and the frost depth level was clearly visible since the soil resembled a layered structure. However, the field studies did not provide the intended basis for further conclusions about how freezing and thawing had influenced the core. The lack of information about compaction, permeability or void ratio of the construction material in its original state made a comparison and evaluation impossible. The expected difference in grain-size distribution because of redistribution of particles upon thawing could not be pointed out. Instead, it was found that the grain-size distributions of material in the core showed a large variation, when comparing diagrams from samples from the moraine pit and archive records. A thermal analysis with the program Temp/W shows possible temperature distributions inside the body of the embankment dam. The analysis takes actual temperatures and water tables during the years 2002 to 2004 into account. On basis of an initial condition, where annual mean temperatures measured during a 30-year period were applied, two different situations with a varying finite element mesh were computed. These two situations resemble the different set-ups of dam crest found in

v field investigation; parts of the dam had a complete dam crest, other parts were subjected to repair work and the removed crest was not completely restored. It was found in all calculations that the frost front advanced considerably to lower levels in the core, with a minimum level for the freezing plane right on top of the core and a maximum level at a depth of about 5 m inside the core. In comparison, visual studies at site showed clearly that the material had been frozen at a depth of 0,8 m. These calculations therefore only give a rough picture of freezing actions. Wind conditions as well as water table, seepage and snow were not included in the calculations. Yet, they are considered to influence the freezing and thawing process significantly. It may even be possible that the freezing plane advances even further down into the body of the dam, thereby seriously affecting and reducing functions of the core as well as those of the filter zones.

vi ZUSAMMENFASSUNG

In der vorliegenden Diplomarbeit handelt es sich um eine Studie des Dichtungskerns des Staudammes in Suorva, welcher hinsichtlich Einwirkungen von Frost- und Tauvorgängen untersucht wurde. Der Staudamm, der 1972 fertiggestellt wurde liegt nördlich des Polarkreises in einer Bergregion, die für kalte Winter und strenge Windverhältnisse bekannt ist. Er ist einer breiten Temperaturspanne und niedrigen Jahresmitteltemperaturen ausgesetzt. Nach ungefähr 30 Jahren seit seiner Erbauung liegt die Annahme nahe, daß Frost- und Tauzyklen im Material des Dichtungskern stattgefunden haben und deren Auswirkungen auf den Dichtungskern, welcher aus einem feinkörningen frostempfindlichen Moränenkies besteht, erheblich sein können. Temperaturen unter null führen zu ‚Frost-Aktionen’ im Boden. Sobald im Boden ein Phasenübergang von Wasser zu Eis stattfindet, bilden sich Eislinsen rechtwinklig zur Richtung des Wärmeflusses. Eis hat die Eigenschaft einer Saugkraft gegenüber ungefrorenem Wasser im Boden, so daß Wasser zur Frostfront wandert, dort gefriert und beim Tauvorgang den ursprünglichen Wassergehalt des Bodens erhöht. Zusätzlich können durch den Eisdruck Steine angehoben werden, was beim Tauen dazu führt, daß die Struktur des Bodens, dessen Porenanteil und Durchlässigkeit, und damit die Durchsickerung erhöht werden kann. Die Funktion des Dichtungskerns als hydraulische Barriere im Innern des Staudammes könnte herabgesetzt werden. Während Felduntersuchungen wurden Schürfgruben gegraben, die zunächst visuell betrachtet wurden. Proben des Dichtungskerns wurden genommen, Wassergehalt, Kornverteilung und Temperaturen gemessen. Jede der vier Schürfgruben wurde in unterschiedlichen Tiefen untersucht, und in zwei Gruben konnte festgestellt werden, daß die Bodentemperatur vergleichsweise niedrig war zu den herrschenden Lufttemperaturen. Speziell in einem Fall lagen die Temperaturen nahe dem Gefrierpunkt, sowohl der Wassergehalt als auch der Feinkornanteil war erhöht. In diesem Fall war es deutlich sichtbar, daß der Boden gefroren war; die Frosttiefe war aufgrund der Schichtung im Boden klar erkennbar. Die Felduntersuchungen lieferten jedoch nicht die erhoffte Basis für weitere Folgerungen bezüglich des Einflusses von Gefrier- und Tauprozessen im Dichtungskern. Fehlende Informationen über Verdichtung, Durchlässigkeit und Porenanteil im ursprünglichen Zustand lassen keinen Vergleich und damit keine weiteren Aussagen zu. Die erwarteten Unterschiede in den Kornverteilungskurven aufgrund von Umlagerungen der Partikel nach Tauvorgängen konnten nicht aufgezeigt werden. Vielmehr wurde eine große Varianz in den Kornverteilungskurven von neuem Material, Proben und Archivaufzeichnungen gefunden. Eine thermische Analyse mit Hilfe des Finite – Elemente Programms Temp/W zeigt mögliche Temperaturverteilungen im Inneren des Staudammes. Die Analyse berücksichtigt die tatsächlichen Temperaturverhältnisse und Wasserstände während der Jahre 2002 bis 2004. Auf der Basis einer Eingangsberechnung unter Verwendung von Jahresmitteltemperaturen, die über einen Zeitraum von 30 Jahren

vii berechnet wurden, wurden zwei unterschiedliche Zustände betrachtet und berechnet. Diese beiden Simulationen spiegeln die tatsächlichen Verhältnisse wider; eine erste Berechnung wurde mit einem kompletten Aufbau der Dammkrone durchgeführt. In weiteren Berechnungen wurde das Netz der finiten Elemente angepaßt. Dieses Netz entspricht dem Teil des Staudammes, der Instandsetzungsarbeiten ausgesetzt war. In diesem Fall fehlt ein Teil der Krone, welche nach den Arbeiten nicht wieder voll hergestellt wurde. In allen Berechnungen konnte festgestellt werden, daß sich die Frostlinie dem Dichtungskerns mindestens nähert und bis zu dessen oberen Kante, maximal aber bis zu einer Tiefe von ungefähr 5 m in den Dichtungskern vordringt. Dagegen zeigten Felduntersuchungen, daß der Kern in einer Tiefe von 0,8 m deutlich sichtbar geschichtet und gefroren war. Diese Berechnungen zeigen also nur einen groben Überblick über solche Vorgänge. Windverhältnisse wurden vernachlässigt; ebenso Wasserniveau, Durchsickerung und Schnee. Es wird allerdings angenommen, daß diese Faktoren bedeutende Auswirkungen auf Frier- und Tauvorgänge darstellen und sich die Frostgrenze in einer größeren Tiefe befindet. Die Funktion des Dichtungskerns sowie die der Filter könnte damit wesentlich beeinflußt und herabgesetzt werden.

viii Table of contents

FÖRORD i PREFACE ii SAMMANFATTNING iii ABSTRACT v ZUSAMMENFASSUNG vii

TABLE OF CONTENTS ix

1. INTRODUCTION...... 1

1.1. BACKGROUND ...... 1 1.2. OBJECTIVE...... 1 1.3. METHOD ...... 2 2. EMBANKMENT DAMS...... 3

2.1. ABOUT DAMS IN GENERAL ...... 3 2.2. DIFFERENT TYPES OF EMBANKMENT DAMS ...... 3 2.3. ZONE DESCRIPTION AND CONSTRUCTION MATERIALS...... 5 2.3.1. Core ...... 5 2.3.2. Filter, transition zones and drainage ...... 6 2.3.3. Supporting fill ...... 7 2.3.4. Rip-rap ...... 7 2.4. DAM FAILURE...... 8 2.5. RIDAS ...... 8 2.6. THE EMBANKMENT DAM IN SUORVA ...... 9 2.6.1. Introduction ...... 9 2.6.2. Historical background...... 10 3. ASPECTS ABOUT CLIMATE AND GROUND THERMAL REGIME...... 11

3.1. PERMAFROST, SEASONALLY FROZEN GROUND AND COLD REGIONS ...... 11 3.2. GROUND SURFACE TEMPERATURES AND ENERGY BALANCE ...... 11 3.2.1. n – Factor...... 12 3.3. ANNUAL MEAN TEMPERATURES ...... 13 3.4. SPECIAL CLIMATIC ASPECTS ASSOCIATED WITH EMBANKMENT DAMS ...... 15 3.4.1. Influence of elevation and snow ...... 15 3.4.2. Influence from reservoir water...... 15 3.4.3. Special features of wind climate at Suorva ...... 15 4. FROST ACTION ...... 17

4.1. IN GENERAL...... 17 4.2. FREEZING AND HEAVING PROCESS...... 17 4.3. THAW WEAKENING AND SETTLEMENT ...... 19 4.4. CYCLIC FREEZING AND THAWING ...... 20 4.5. STONE HEAVE AND SORTING OF PARTICLES...... 21

A documentation of the Eastern Suorva dam core ix Table of contents

5. DOCUMENTATION OF FIELD INVESTIGATION ...... 22

5.1. DESCRIPTION OF PRACTICAL WORK ...... 22 5.1.1. Sampling ...... 22 5.1.2. Documentation...... 23 5.1.3. Field laboratory ...... 23 5.2. RESULTS OF FIELD INVESTIGATIONS...... 23 5.2.1. PG ÖD 650 – Eastern Dam Section 650...... 24 5.2.2. PG ÖD 700 – Eastern Dam Section 700...... 26 5.2.3. PG ÖD 750 – Eastern Dam Section 750...... 28 5.2.4. PG ÖD 200 – Eastern Dam Section 200...... 33 5.3. COMPARISON AND EVALUATION...... 36 5.3.1. Comparison of particle-size distribution ...... 36 5.3.2. Evaluation of samples and their grain-size distribution ...... 38 5.3.3. Limitations in sampling and discussion ...... 39 6. THERMAL ANALYSIS...... 40

6.1. INTRODUCTION ...... 40 6.2. DEFINITION OF THE PROBLEM...... 41 6.2.1. Drawing the problem ...... 41 6.2.2. Specification of functions and analysis type...... 43 6.3. MATERIAL PROPERTIES ...... 44 6.3.1. In general ...... 44 6.3.2. Heat transfer processes ...... 45 6.3.2.1. Conduction and convection...... 45 6.3.3. Thermal properties of soils...... 45 6.3.3.1. Latent heat...... 46 6.3.3.2. Specific heat capacity ...... 46 6.3.3.3. Thermal conductivity ...... 47 6.3.4. Material data for computation...... 49 6.3.5. Temperature function ...... 50 6.4. SOLVING THE PROBLEM ...... 51 6.5. STEADY-STATE ANALYSIS AN BOUNDARY CONDITIONS ...... 52 6.6. RESULTS OF THE THERMAL ANALYSIS ...... 53 6.6.1. Results for a construction with complete dam crest ...... 53 6.6.2. Results for a construction without dam crest...... 56 6.7. SUMMARY AND DISCUSSION ...... 59 7. CONCLUSIONS...... 60 8. REFERENCES...... 61

A documentation of the Eastern Suorva dam core x 1. Introduction

1. Introduction

1.1. Background

The embankment dam in Suorva is located in northern Sweden and was built during the years 1966 – 1972. It regulates one of Sweden’s most important hydro power sources with a capacity of the reservoir up to 5.900 million m³ water. The mountain valley above the polar circle in the upper reaches of the Lule River belongs to cold regions with deep seasonally frozen ground. The annual mean temperature ranges from -1°C to -0,4 °C and severe wind conditions lead to the assumption that the core of the embankment dam may be affected by repeated freezing and thawing. During construction works at the dam, where the dam crest was removed and the moraine core was raised, the original material in the core was analyzed to ensure the quality of the material. In combination with these works, the possibility of further investigations regarding freezing and thawing cycles was given. Cyclic freezing and thawing influences the structure in soil; studies on fine-grained soils reported changes in volume and structure as well as significant increases in permeability. Such changes can have an impact on seepage flow; thereby reducing the function of the core is significantly. Temperature and climate in this northern region provide conditions for such repeated freezing and thawing actions. A practical part, including a field study of the earth fill in the central core was carried out in order to find out if and in which way effects of freeze/thaw cycles influenced the characteristics of the material as hydraulic barrier. In addition, a theoretical part was supposed to simulate the possible influence of temperature and climate with the help of the finite element method, Temp/W.

1.2. Objective

This MSc thesis was carried out in order to analyze if the moraine core of the rock fill dam in Suorva was influenced by freezing and thawing. Several sections are included in this comprehensive aim. A first step was to conduct field studies and to obtain samples from test pits at the Suorva dam for analysis of the material in the laboratory. Further, it was intended to collect information about temperatures and climate to give an insight of possible actions in the hydraulic barrier of the dam. Effects of temperatures below the freezing point and freeze/thaw cycles on soil are presented. A thermal analysis with the finite element program Temp/W showed how far the results from field studies can be compared to theoretical calculations of frost depth inside of the dam, and to which extend the moraine in the core as well as filter zones are affected by freezing conditions. The objective was to demonstrate that such freezing conditions influence the embankment dam and that frost has to be taken into account in such constructions in cold regions.

A documentation of the Eastern Suorva dam core 1 1. Introduction

1.3. Method

On basis of general information the two major parts of this MSc thesis are presented, a practical part of field work and a theoretical part that consists of a thermal analysis using the finite element method. An introduction about embankment dams in general, different types and different materials which can be used for construction, as well as basic rules for construction and causes for dam failure and dam safety guidelines are explained. A short historical outline presents the embankment dam in Sourva and its background for construction. Aspects of climate and ground thermal regime explain the classification of permafrost and seasonally frozen ground and the interrelation between air and ground temperatures. The temperature profile in the ground is dependent on several factors; the energy balance at ground surface has to be regarded. For calculations, the annual mean temperature has to be taken into account. A next step considers the effects of climate on soils in general. Thermal processes in the ground such as freezing and thawing lead to frost action. This term includes frost heave, thaw weakening and settlement. Altered structures in fine-grained soils have been found. Cyclic freezing and thawing affects the structure in soil; changes in volume and permeability have been reported. The phenomenon of stone heave and redistribution of grains is explained. With this basic information, the practical part of field work is presented. The method of investigation, sampling and analysis in the field laboratory is explained. Results from samples from different test pits are described and illustrated with pictures and diagrams. A discussion at the end of this chapter includes a summary of the visual inspections and the results from laboratory work, as well as an evaluation and some thoughts about limitations in field works. Finally, a thermal analysis with the help of the finite element program Temp/W is carried out in order to calculate the temperature distribution inside a rockfill dam. This method is chosen for comparison of practical and theoretical results. Because of the inexistence of knowledge about such calculations in connection with embankment dams, thermal properties and the choice of values for indata are explained in detail. Temperature data was obtained from the Swedish Meteorological Institute SMHI, and five-day mean values for the seasons winter 2002/2003, summer 2003 and winter 2003/2004 were used for calculation, so that the result can be compared to the situation during field investigations in summer 2004. The results of the computation are presented and discussed, and a comparison to practical results completes this thesis.

A documentation of the Eastern Suorva dam core 2 2. Embankment dams

2. Embankment dams

2.1. About dams in general

A dam is a barrier to hold back water, it is man-made and usually either constructed of concrete or natural material such as soil or rock. It can have several purposes: water supply, production of hydropower, flood control, irrigation, navigation or recreation. There are different types of dams, such as arch dams, buttress dams, embankment dams and gravity dams. A main factor for the choice of structure and material is the local situation, i.e. the possibility for foundation and the shape of a valley. An arch dam is made out of concrete which is curved and has the shape of an arch pointing back down into the water reservoir. It has a strong set-up to counteract forces from the water behind the dam and is usually built in narrow and steep valleys. A buttress dam has a water-tight lining on the upstream side which is supported by triangular walls which are called buttresses. It can be made out of concrete or masonry. Gravity dams, also made of concrete or masonry, have a mainly triangular shape in cross section, and are quite massive, so that gravity is the main force to hold back water. Contrary to these constructions, embankment dams are made of natural materials. They can be built on hard rock or soft soils, as well as in wide valleys, since they do not impose too much pressure on the foundation in contrast to the previous types. The different types of embankment dams will be explained in the following section. Sweden has 190 hydropower dams which are classified as high dams according to ICOLD, the International Commission on Large Dams. A common definition of a high dam is height of more than 15 m from the foundation level to the dam crest. For comparison, the number of dams in Sweden corresponds to 21,5 dams per 1,000,000 inhabitants. 50 % of them are earth- and rock fill dams, 37% are rock fill dams. In Germany 311 dams are classified as high dams, an average of 3,8 dams per 1,000,000 inhabitants.

2.2. Different types of embankment dams

There are several types of embankment dams, and the designs depend on the topography, the foundation conditions, the planned height of the dam, and on the availability of construction materials. Embankment dams are divided into earth fill and rock fill dams, and in homogeneous or zoned dams. A rock fill dam is defined as an embankment dam which mainly consists of natural stones and boulders, or fill material from quarries or rock excavation sites, whereas an earth fill dam primarily is made up of clay, silt, sand, or gravel.

A documentation of the Eastern Suorva dam core 3 2. Embankment dams

A basic and simple construction is a homogeneous earth fill dam made up of clay, silt, sand or gravel-sand-clay soils. The fine-grained soil is supposed to provide an overall low permeability which is approximately equal in both horizontal and vertical direction. It is suggested to use this type of dam for less than 5 m height, since seepage or erosion control is missing [Fell, 1992]. A homogeneous earth fill dam may have a toe drain with permeable rock or gravel to attract water, thereby lowering the seepage line. Such a construction may be used for higher dams. A recommendation is a level of 10 m height, see Figure 2.1 a. Zoned embankment dams comprise diverse construction materials with different permeability rates with regard to the section of the dam. The hydraulic barrier is often made up of earth fill material such as clay or fine-grained till. It may also consist of concrete, asphalt or bitumen. These materials can be embedded in the supporting fill as central core, but also be placed on the upstream slope surface, see Figure 2.1 b, c and d [Kjærnsli, 1992].

a)

b)

c)

d)

Figure 2.1: Different types of embankment dams [Kjærnsli, 1992]

A documentation of the Eastern Suorva dam core 4 2. Embankment dams

A common construction is a rock fill dam with a central earth fill core. The cross- section is composed of an impervious core, filter zones, transition zones and supporting and stabilizing fill material, see Figure 2.2. Different sections meet different requirements in the structure; as the core (section 1 in Figure 2.2) controls seepage, the filter (section 2 and 3 in Figure 2.2) controls internal erosion and drainage and rockfill material (section 4 in Figure 2.2) stabilizes the whole structure. Fine-grained earth fill material with low permeability is used for the core, which is flanked by filter zones upstream and downstream. Such zones are made of coarse- grained material and act as filter. They can consist of sandy gravel, but can also be made of sharp-edged crushed rock. The grain-size distribution and permeability varies according to their placement. A general rule is that the material becomes coarser and more permeable towards the outside, thereby lowering the seepage level and assuring proper drainage. Embankment dams with a central impervious element are suitable for large constructions and the side slopes can be steeper than the side slopes of an earth fill dam. The core of the dam may be central or sloping towards the upstream reservoir.

Figure 2.2: Explanation of terms for a typical embankment dam with symmetrical cross-section and central core [Kjærnsli, 1992]

2.3. Zone description and construction materials

2.3.1. Core

The core of the dam, also referred to as the impervious element, is made up of earth fill material. It limits the seepage through the dam and is supposed to ensure a reasonable low permeability. In Sweden, the use of moraine, a glacial till with a complex grain-size distribution ranging from fine-grained material such as clay and silt up to gravel, stones and boulder, is most common. Such hydraulic barriers are

A documentation of the Eastern Suorva dam core 5 2. Embankment dams predominant since large deposits in mountain areas in economic hauling distance can be found. According to Vattenfall (1988), the requirements for the core are following: • The fine-grain content < 0,06 mm ranges from 15-40 % of material < 20 mm. • The content of fines is less than 40 % of material < 20 mm. • A minimum amount of 70 % of grains passing 64 mm is < 20 mm. • A maximum amount of 85 % of grains passing 64 mm is > 2 mm. • A permeability of 3 x 10 –7m/s to 3 x 10 –9m/s. • Large boulders may occur, but a maximum size of two thirds of the placement layer thickness may not be exceeded. A maximum diameter is 300 – 400 mm.

The content of fines is restricted and should not be excessively high. A high amount of fines in the core in turn requires a higher amount of fines in the filter and transition zones. [Kjærnsli, 1992]

2.3.2. Filter, transition zones and drainage

The filter can be divided into different filter zones, such as fine filter and coarse filter; according to the zone it is placed. The fine filter, next to the impervious element downstream, prevents the core from inner erosion by seepage water and reduces the water pressure. It is regarded as the most important part of the dam, since internal erosion and leakage is one of the major reasons for damage. The coarse filter, or transition zone, protects the fine filter from erosion, i.e. suffusion and piping, so that a stable layer around the core is created. Thus, strict particle-size criteria have to be met to assure filter stability. The filter has to be cohesion less, with a linear particle-size distribution, and it has to resist compaction during working processes so that the particle-size distribution is not affected. In addition, the size of stones is restricted in order to avoid separation of the material.

The following Table 2.1 summarizes the rules of filter criteria in relation to different base materials:

Table 2.1: Rules for filter criteria [RIDAS, 2004] Base material Base material Content of fines < 30 % Content of fines 30 – 80 %

4 < D15/ d15 < 40 4 < D15/d85 D15/d85 < 4 D15 < 0,7 mm

D50/d50 < 25 D50/d50 < 25

The letters D and d represent the grain-size of filter and base material, respectively.

A documentation of the Eastern Suorva dam core 6 2. Embankment dams

Corresponding to these rules, the grain-size in fine and coarse filter may be defined by the following limits for different fractions:

Table 2.2: Example of fractions for filters for the Eastern Suorva dam

Fine filter Coarse filter

D15 = 0,3 – 0,7 mm D15 = 8 - 20 mm D50 = 1,2 – 8,0 mm D85 = 20 – 60 mm D85 = 5,0 – 20 mm Dmax = 75 mm Dmax = 25 mm

In general, the filter material has to be suitable in comparison with the base material of the adjacent zone, so that acceptable particle-size distributions vary with the range of the grain-size distribution of the core. If the core consists of a well-graded material such as moraine, the limits for the filter criteria are narrow. In contrast, the limits may vary more as the core material is less variable [Kjærnsli, 1992]. Coarse filter and transition zones provide proper filter stability in adjacent zones and are responsible for further drainage. The coarser filter must fulfil the same rules as in Table 2.1. [RIDAS, 2004]

2.3.3. Supporting fill

Fill material such as stones, boulders, and rock are responsible for support and stability of the construction. Shape, size distribution and strength of individual stones and rock are responsible for overall strength, slope stability and compressibility of the rock fill. Stones are placed into a slope and hold in place by the natural slope angle which equals more or less the angle of friction [Kjærnsli, 1992]. Seepage and drainage influence the pore pressure in the core and the filter and can reduce the stability of the dam. The supporting fill must not be subjected deformation and erosion, as this may lead to displacement and damage in the core.

2.3.4. Rip-rap

Especially the upstream slope is exposed to wave action or ice forces and has to be prevented from erosion. This outer layer of rock fill called rip-rap protects the slopes from climatic impacts such as rain. The rock pieces have to have a sufficient size and weight and must be placed in a way that waves and ice do not affect stability.

A documentation of the Eastern Suorva dam core 7 2. Embankment dams

2.4. Dam failure

General causes of dam incidents are overtopping, embankment leakage or piping, foundation leakage or piping, flow erosion, slope protection damage, and deformation. According to ICOLD, the International Commission on Large Dams, the most common causes of failure of earth and rock fill dams is overtopping, internal erosion of the body of the dam, and failure of the foundation [Fell, 1992]. This survey was carried out in 1973 and showed the following distribution of causes for dam failure from 1900 to 1975, see Figure 2.3.

Dam failures 1900 - 1975 (over 15 m height)

Others, 6%

Overtopping, 35% Piping and seepage, 38%

Foundation leakage, 21%

Figure 2.3: Causes for dam failure [Fell, 1992]

2.5. RIDAS

The Swedish dam safety guidelines, named RIDAS, contain general rules which are not enforced by law, but by the individual dam owner. Review of these rules is a formal task of the Water Rights Court. The dam owner is responsible for the design, construction, operation and maintenance of a dam, so that risks or serious consequences are eliminated or reduced as far as possible. In addition, action plans have to be provided in case of an incident, and a long term perspective for dam safety has to be considered. These guidelines were called RIDAS. They were presented in 1997, and a revised version came out in 2002 [Mill, 2001]. According to RIDAS, dams are categorized in classes 1, 2 and 3, depending on the consequences in case of dam failure. These classes are defined according to the risk of loss or damage of human life, and loss or damage of social, environmental and economic values. Class 1, for example, represents the circumstance of high hazard, where severe consequences of failure are regarded. For a high hazard dam, the dimensioning is based on a flood appearing once every 10.000 years. It includes a clear risk for loss or damage of human life, or a possibility for that which must not be disregarded. A low hazard dam the design flood is appearing once every 100 years [RIDAS, 2004].

A documentation of the Eastern Suorva dam core 8 2. Embankment dams

2.6. The embankment dam in Suorva

2.6.1. Introduction

The embankment dam at Suorva is located in the region of a mountain valley north of the Arctic Circle in the upper reaches of Lule River. The river is Sweden’s most important hydro power source. The reservoir regulated by the Suorva dam is about a 60 km long area of originally five lakes. Suorvajaure, as the reservoir is called is Sweden’s second largest with a capacity of 5.900 million m³ water, see Figure 2.4.

Figure 2.4: Location of the embankment dam in Suorva

The Suorva dams are three different dams, East Suorva dam, Sågvik dam, and West Suorva dam. The rock fill dams were constructed during the years 1966 until 1972. The total length of the crest is 1370 m; the length of the Eastern dam which is subject to this thesis is 780 m. All three dams have an impervious central core of moraine. They are all founded on rock with a grout curtain beneath the central core. A schematic cross-section of the East Suorva dam is shown in Figure 2.5, where the different zones are numbered: 1 rock fill, 2 moraine core, and 3 filter zone. In the figure, the original concrete dam is included, which was built in 1919 and extended and raised in two following construction stages.

A documentation of the Eastern Suorva dam core 9 2. Embankment dams

Figure 2.5: Cross-section of the Eastern Suorva dam, including the first construction of concrete and the rock fill dam constructed later. Note the different sections: 1: Rock fill, 2: Moraine core, 3: Filter zone.

2.6.2. Historical background

Due to the industrialization at the beginning of the 19th century, the mining of iron ore and the increased need for transportation by railway, the possibility to make use of Lule River’s waterpower was examined as early as 1908. Iron ore was an important economic factor, electric locomotives had a much better capacity, and import of coal was expensive. Industry and society needed inexpensive energy supply, which should be independent from coal. The company Statens Vattenfallsverk, which today is Vattenfall AB, had been established in 1909, originally to make use of energy from waterfalls and to explore the Swedish governments’ rights for exploitation. It was Vattenfall that started construction works in Suorva in 1919, even though the decision for the regulation of Lule River and the construction of the embankment dam was taken by Swedish authorities in 1921. The demand for hydro power obviously had been urgent. During the first construction in 1919 - 1923 a concrete valve dam was built. Its regulation level was raised twice, until the old concrete dam finally was replaced by a rock fill dam located on the downstream side of the original dam in 1966 - 1972. The different stages in construction history at Suorva are summarized in the following Table 2.3. Table 2.3: Construction stages of the Suorva dam Construction Stage 1 2 3 4

Construction Period 1919-1923 1937-1941 1942-1944 1966-1972 Maximum water level 428,9 435,7 438,8 453,0 Minimum water level 420,4 420,4 420,4 423,0 Regulation height [m] 8,8 15,3 18,4 30,0 Height of dam [m] 67 m Reservoir Vol. [million m³] 1020 2190 2750 5900

A documentation of the Eastern Suorva dam core 10 3. Aspects about climate and ground thermal regime

3. Aspects about climate and ground thermal regime

3.1. Permafrost, seasonally frozen ground and cold regions

Frozen ground is generally defined as soil or rock with a temperature below 0 °C. This definition is completely dependent on temperature and gives no information about the content of water or ice. If the temperature in the ground remains below the freezing point throughout two subsequent winters and the intermediate summer, the term permafrost is applied. If the ground is only frozen during the winter period it is referred to as seasonally frozen ground. With respect to air temperatures, depth of ground freezing, snow depth, or ice cover on lakes, cold regions are characterized. Such areas are assumed to have a minimum frost penetration to a depth of 0,3 m which occurs at least once in 10 years. This frost depth is specified by an approximate freezing index of 55 °C days, i.e. a summation of the mean daily temperatures below zero. For example, a freezing index of 55 °C days implies that e.g. 11 days had a mean daily temperature of -5 °C. Cold regions are divided into permafrost or seasonally frozen ground. Continuous and discontinuous permafrost regions may be found in Polar Regions, such as Alaska, Canada, or Siberia. Scandinavia, despite high latitude, belongs mainly to countries with seasonally frozen ground, together with parts of the United States and Asia. Nevertheless, there are some areas found in Scandinavia which belong to the category of discontinuous permafrost.

3.2. Ground surface temperatures and energy balance

Temperatures in the ground are determined by air temperatures, heat flow from the inner earth, and thermal properties of the soil. Yet, the heat flow penetrating the soil from ground surface is not the same as air temperature, but depends on climatic factors. Such factors include solar radiation, wind and cloud conditions, or snow cover. Furthermore, vegetation cover, evaporation of moisture, colour, latitude, season and time during the day influence the temperature transfer from the air to the ground. Solar radiation, wind and air temperatures are essential climate factors for the temperature at ground surface [Hermansson, 2002]. Together with solar radiation, convective heat flow and evaporation (or condensations) are involved when considering energy balance. Solar radiation is short wave, and is influenced by latitude, cloud cover and atmospheric conditions. Radiation does not completely reach the surface, but can be directly or diffusely scattered, i.e. parts are reflected from the surface and parts are reflected by clouds. Radiation reflected from surface to space is long wave radiation. Convective heat flow is due to wind velocity, air turbulence and relative air and ground temperatures. The schematic description in Figure 3.1 summarizes the heat balance between air and surface.

A documentation of the Eastern Suorva dam core 11 3. Aspects about climate and ground thermal regime

Figure 3.1: Different climatic effects on ground surface [Hermansson, 2002]

3.2.1. n – Factor

The temperatures at ground surface are not equal to air temperatures, and some of the different influences which contribute to this discrepancy have been discussed in the previous section. An attempt to take the character of the ground surface into account is the consideration of the n-factor. The n-factor is defined as the ratio between the air and ground surface temperatures. This factor is used for calculating a value for the ground surface temperature [Phukan, 1985]. It is dependent on vegetation and surface colour and supposed to account for effects of wind and solar radiation, see Figure 3.2.

Surface Thawing factor nt Freezing factor nf Snow - 1,0 Pavement free of snow and ice - 0,9 Sand and gravel 1,0 – 2,0 0,9 Turf 1,0 0,5 Spruce 0,35 – 0,53 0,55 – 0,9 Spruce trees, brush 0,37 – 0,41 0,28 Willows 0,82 - Weeds 0,86 - Gravel fill slope 1,38 0,7 Gravel road 1,99 - Concrete road 2,03 0,8 Asphalt road 0,96 – 1,25 0,8 White paint surface 0,98 – 1,25 - Figure 3.2: Different n-factors used for estimation of the surface temperature [Phukan, 1985]

A documentation of the Eastern Suorva dam core 12 3. Aspects about climate and ground thermal regime

3.3. Annual mean temperatures

Temperature measurements in Sweden are carried out by the Swedish Meteorological and Hydrological Institute SMHI, which has published measured annual mean temperatures for time periods of 30 years. The records show that the annual mean temperatures in Sweden ranges from -2 °C to 8 °C. This value represents the 30-year average for the years 1931 – 1960. In Luleå, the mean annual temperature during this time period was 2,5 °C, while the temperatures further up north in the mountain region around Suorva was approximately -1 °C, see Figure 3.3 [Taesler, 1972].

Luleå

Figure 3.3: Mean annual temperatures in Sweden 1931 – 1960 (SMHI, 1991)

A documentation of the Eastern Suorva dam core 13 3. Aspects about climate and ground thermal regime

A temperature change has been noticed during the following 30-year period from 1961 – 1990; the mean annual difference between temperatures observed during the latest 30-year-period and the previous has been noted to be up to 0,6 °C. This difference is shown in Figure 3.4. One has to consider that the negative value on the map represents an increase in the annual mean temperature, i.e. the 30-year average annual mean temperature for Suorva, during 1961 – 1990, is -0,4 °C [Alexandersson, 1991].

Figure 3.4: Difference between the average mean annual temperatures measured during time periods 1931 – 1960 and 1961 – 1990 (SMHI, 1991)

A documentation of the Eastern Suorva dam core 14 3. Aspects about climate and ground thermal regime

3.4. Special climatic aspects associated with embankment dams

3.4.1. Influence of elevation and snow

Influence of elevation and cold air sinking during night time can have a significant effect on temperature. During winter, one has to take snow cover into account. Since snow has a low thermal conductivity, it acts as an insulation layer. It also reflects solar radiation, which results in a higher freezing index. Strong winds are mentioned in connection with snow, forcing it to accumulate in certain areas and increasing the water content when melting. However, such features may be neglected as it has been observed that winds in the mountain valley, where Suorva is located, are quite strong and only a small amount of snow covers the Suorva dam during winter time.

3.4.2. Influence from reservoir water

The temperatures in an embankment dam depend on air temperatures and water temperatures in the upstream reservoir [Johansson, 1997]. These temperatures vary seasonally. In Johanssons investigations, the seasonal variation of the air temperatures are found to be neglectable at a depth of 10 m from the crest of the dam; it is assumed that the influence becomes less than 1 °C at this depth. The internal temperature below the water line in the body of the dam is mainly controlled by seepage and therefore dependent on water temperatures.

3.4.3. Special features of wind climate at Suorva

The valley at Suorva is known for severe wind conditions with an annual average mean wind speed of 7,85 m/s measured on a 35 m high tower situated between the Eastern dam and Sågviks dam. This number is considered remarkably high for an inland location. For comparison, average wind speeds at coastal sites were measured with 6,9 to 7,0 m/s. A study about the wind climate in the valley conducted in connection with a wind power station showed that the mountain valley with its main direction from northwest to southeast has channelling effects on wind. The mountains on both sides of the valley have a height of about 1200 m to 2000 m. It was found that winds passing through the valley meet mountain tops and are forced to pass along the valley, thereby increasing the wind speed. This channelling force is supported by a low pressure gradient along the northwest to southeast axis created by winds passing in perpendicular direction. The lower air pressure along the valley additionally supports the airflow and its acceleration in direction of this axis. An additional factor for the high mean wind speed may be the bending of the valley at Suorva, thus possibly increasing the channelling effect.

A documentation of the Eastern Suorva dam core 15 3. Aspects about climate and ground thermal regime

Measurements of wind speed at Suorva at 10 m height show an annual mean value of 7,0 m/s in 1998, 6,9 m/s in 1999, and 7,3 m/s in 2000. A mean value for the period from 1995 until 2001 is 6,9 m/s. The term wind chill is generally not suitable in context as it is particularly related to the loss of body heat. However, a comparison may give an idea of how these wind velocities probably may influence the temperature conditions. Wind chill is the cooling effect on skin; it is related to wind velocity and air temperature. Already at a wind speed of 4 – 6 m/s can a temperature of +5 °C be experienced as temperature below the freezing point, see Figure 3.5. For higher velocities and lower air temperatures is this effect even more extreme. The following Figure 3.5 shows comparative temperatures felt at different air temperatures under varying wind conditions. It has to be noted that this does not apply to the actual problem regarding the Suorva dam; it may only be used to give an impression of wind effects.

Figure 3.5: Cooling effect of wind. Comparative temperatures felt at different wind velocities [Hassi et al., 2002]

A documentation of the Eastern Suorva dam core 16 4. Frost action

4. Frost action

4.1. In general

The term frost action refers in general to three features: frost heave, thaw weakening and thaw settlement. Apart from the fact that soil in its frozen state may introduce positive properties such as strength, increased bearing capacity and impermeability, does the process of frost action also involve negative effects to engineering constructions. Frost action occurs in frost-susceptible soils, when temperatures are sufficiently low and water for freezing and ice lens formation is available. Frost heave results from freezing of the soil. Water in the ground undergoes a phase change from fluid to solid state, thereby increasing its volume. Yet, it is not only water freezing in situ in the voids that is responsible for the expansion, but also unfrozen water migrating and turning to ice at the freezing front. The accumulation of ice results in increased water content when the soil thaws. Consequently, the bearing capacity is reduced. Effects of frost action are changes in volume and water content, as well as loss of shear strength and bearing capacity. Cyclic freezing and thawing influences the structure and permeability. Both may have significance for fill material in the core of an embankment dam. In order to explain the aim of field investigations and to provide a basis for a following discussion, possible impacts by frost on soil will be discussed in this section.

4.2. Freezing and heaving process

Temperatures below the freezing point create a temperature gradient in the soil with a 0 °C isotherm proceeding down in the ground at a rate according to temperature, climate, and the soils thermal properties. The frost front moves downward into the ground, creating ice lenses parallel to this freezing plane and lifting the soil vertically in direction of heat flow. To describe the freezing process and ice lens formation, a volume of soil exposed to negative temperatures is considered, containing a frozen part where ice lens formation already have taken place. The continuing movement of the frost front down in the ground results in further freezing. At 0 °C, water can exist in frozen or liquid state. In this zone, pores may partly be filled with ice, which impedes the undisturbed flow of water. Ice creates a suction potential and is responsible for water flow to the frost front from lower regions. The amount of water migration is dependent on soil properties, mainly grain-size and hydraulic permeability. Water reaches the frost front from lower levels and accumulates in the region of the active ice lens. Progressive freezing results in a new ice layer. The soil skeleton is lifted up when the pressure of the ice formation is greater than that of overburden, and uplifting of soil

A documentation of the Eastern Suorva dam core 17 4. Frost action particles creates new space for the ice lens. Figure 4.1 shows the principle mechanism of ice lens formation and frost heave.

Figure 4.1: Mechanism of frost heave [Andersland/Ladanyi, 1996]

When water freezes, its volume expands by 9 % of the original value. Assuming normal values for void ratio and water content in soil, e.g. unsaturated soil, such an increase would result in 2-3 % total extension upon soil freezing. The volume increase can be compensated by unfilled voids, presuming that the pore water is not pressed out of the voids. Water may be pressed out in coarse-grained soils, where the permeability is larger than in fine-grained soils. However, frost heave is due to the additional process of water migration to the frozen fringe. The frozen fringe is the area below the frozen soil and the active ice lens, where unfrozen water is transported to. At this level, pores are partly filled with ice and the permeability is reduced. The soil is therefore lifted up to a greater extend than what would be expected to occur in volume change by plain freezing of in situ pore water. Factors influencing the thickness of an ice lens and the spacing in between ice lenses are soil type, the homogeneity of the material, the availability of water and uniformity of its supply. Finally, the temperature gradient is essential. If the water supply is sufficient and equals the rate of latent heat extraction, ice lens growth proceeds. In case of an exceeding heat-removal rate and lesser water migration, the temperature decreases and the freezing plane advances to a new location where moisture is provided. Hence, thicker ice lenses develop at a smaller temperature gradient, and thinner ice lenses at larger temperature gradient. [Andersland/Anderson, 1978]

A documentation of the Eastern Suorva dam core 18 4. Frost action

4.3. Thaw weakening and settlement

Thawing starts at the surface and advances deeper down in the ground. The problem with this process is the blocked drainage because of a border of soil below which is still frozen. The rate of thawing, i.e. the rate of water liberation, controls the impact on shear strength. If ice lens thawing occurs at a fast rate, excess pore water pressure because of blocked drainage will considerably reduce the shear strength and the bearing capacity. Thaw weakening affects mostly fine-grained soils, since the possibility for drainage is lower than in coarse-grained soils. Sand and gravel are regarded as being stable under thawing conditions, while fine-grained soils such as silt and clay suffer from their low permeability. Pore water produced during thawing may be able to migrate if the thawing rate is considerably slow. The soils stability is not affected in this case, and settlement occurs close to the same rate.

Settlement because of thaw consists of two parts. The inverse phase change from ice to water decreases the volume to its initial state. Besides that, a further settlement is observed when drainage of the thawed soil takes place. Especially in fine-grained soils, where ice segregation occurs and the water content is higher after thaw than before freezing, drainage results in additional consolidation.

Figure 4.2 shows that settlements occur already when the soil is frozen and load is applied. However, these settlements are small in comparison to settlements during thawing, where a significant reduction in volume is observed. The descending line in unfrozen state shows the following process of consolidation, where excess pore water is expelled.

Figure 4.2: Thaw-settlement behaviour [Viklander, 1997]

A documentation of the Eastern Suorva dam core 19 4. Frost action

4.4. Cyclic freezing and thawing

In general, the process of freezing causes water to migrate, freeze, increase the volume of the soil, and finally the soil skeleton to move. Pressure created by ice breaks up bonds between particles and lifts them up. In contrast to that, thawing generates melting water which is pressed out. Thaw settlement and consolidation, causing movement of particles and rearrangement in the skeleton, are the result. It has been observed that fine-grained soils exposed to freezing and thawing undergo structural changes. These changes are not similar for fine-grained and coarse-grained soils, but differ because of cohesion, specific surface of particles and the amount of bound water, which normally gives higher water content. A clayey soil may show different regions: cracks filled with ice and shrinkage because of negative pore pressure close to the frost front. Cracks, ice lenses or fissures are alternating bands with varying thickness. Such spaces will not be completely closed in fine-grained soils during thawing because of cohesive forces. Water filled cracks create new paths for water to flow through the soil. A coarse-grained soil, on the other hand, has a self-healing capacity because of the lack of cohesion. Effects on permeability and volume depend on the initial void ratio and the degree of compaction. An originally loose soil with a small degree of compaction shows a volume increase during freezing and after that an extended decrease of volume upon thawing. In this case, the void ratio and the permeability finally will be decreased, since particles move closer together after each cycle. After a number of repeated freeze/thaw, a residual void ratio is reached and the permeability has a lower value than at the beginning. Tests with 10 cycles have been reported, and the permeability decrease was noted with up to 50 times. In contrast to that, a dense and more compacted soil showed a void ratio and permeability increase up to 11 times. Repeated freeze/thaw loosens the structure of the soil, and again, the void ration reaches a residual value [Viklander, 1997]. This effect is shown in Figure 4.3.

Figure 4.3: Void ratio after a number of freeze/thaw cycles [Viklander, 1997]

A documentation of the Eastern Suorva dam core 20 4. Frost action

4.5. Stone heave and sorting of particles

A further effect of freezing and thawing is the phenomenon of the migration of particles, movements of grains and stone heave. The separation of coarser and finer particles, i.e. stone heave, occurs in vertical direction, with a movement of coarser grains upwards towards the ground surface, where lower temperatures prevail. To explain the process of stone heave, a volume of soil is considered, containing a stone surrounded by some finer material. When the frost front advances down in the ground, the soil which covers the stone is lifted up during freezing. For the stone to follow this movement upwards, the frost front has to move further down, and the adfreezing force is increased. The stone is then lifted up, and by filling the space above the stone a new cavity is created underneath. The stone is not lifted up further when the freezing line has advanced deeper down below this space during this freezing process. Further uplifting may occur in following freeze/thaw cycles. In laboratory tests, stone heave was found to be largest after approximately six to nine cycles. [Viklander, 1997]

Particles are redistributed when the soil thaws. As the stone has a higher thermal conductivity than the surrounding soil and more thermal energy passes through the stone, the ice underneath melts. Fine particles move with water produced during this melting process and fill the space below the stone so that it cannot move back to its original position. The initial structure in the volume of soil is altered.

Figure 4.4: Principle of stone heave [Viklander, 1997]

A documentation of the Eastern Suorva dam core 21 5. Documentation of Field Investigation

5. Documentation of Field Investigation

5.1. Description of practical work

For field investigation, test pits with a side length of 2 – 4 m were excavated by the help of an excavator. Visual investigations as well as collection of samples from four different test pits were expected to give information if the core of the dam had been exposed to freezing and thawing cycles. It was also assumed to give information about in which way such potential frost action had influenced the fill material. If freezing occurred, the material is expected to be layered; giving differences in the grain-size distribution, the water content or varying dry density may be detected. Additionally, since parts of the Eastern Suorva dam were exposed to some repair work, the crest of the dam was not restored completely in 1983, but temporarily covered with an insulation layer, hold in place by boulders. Samples taken from parts covered with the original crest compared with samples from provisionally covered parts were thought to give valuable information for this project. The test pits were numbered according to the dam section, i.e. the distance from the northern starting point of the dam. In the context of the ongoing construction work the quality of the existing fill material had to be assured. Hence, samples from test pits were taken at 100 m distance where the original dam crest still existed, and at 50 m distances where the dam crest had not been fully re-established. Since the time period for sampling in terms of this thesis did not fully cover the construction works, four test pits were chosen for analysis and comparison.

5.1.1. Sampling

Disturbed samples were collected from test pits, at different levels; 0,0 m, 0,5 m, 1,0 m, 1,5 m, and 2,0 m. Date, location and depth was registered, so that the samples could be stored in plastic bags and containers for transportation and further laboratory testing. First, the rock fill and gravel as well as the insulation layer on top of the core had to be taken away. In order to obtain representative samples, a thin layer with a thickness of approximately 10 – 15 cm on top of the earth fill was scraped away. In addition, since the test pits were measuring approximately 3 x 3 m, parts of the soil were taken at different spots on the base of the actual layer. Pictures were taken during sampling to show the sides of the trenches where the possible presence of different layers or accumulation of water was visible. The test pits and samples where numbered according to the dam section, as mentioned before; and will be referred to PG ÖD 650, PG ÖD 700, PG ÖD 750 and PG ÖD 200. The numbers for the pits were taken over from the Swedish labelling, where PG stands for test pit, ÖD implies that samples come from the eastern dam, and the number defines the section of the eastern dam.

A documentation of the Eastern Suorva dam core 22 5. Documentation of Field Investigation

5.1.2. Documentation

For documentation of the condition of the moraine core, as well as how excavation and sampling work were carried out, photos where taken. A number of approximately 50 – 60 pictures was taken at each excavation site, depending on the structure of the core and on possibly exhibited special features concerning accumulation of stones or moisture. In addition, the temperatures were measured in two cases, PG ÖD 700 and PG ÖD 750, since the soil felt unusually cold during sampling.

5.1.3. Field laboratory

The analysis of the grain-size distribution and the water content of the samples were carried out in the field laboratory. To find out the water content, some of the samples were stored directly in plastic bags at investigation site and taken to the field lab. In the field lab an oven was available for drying according to standard rules.

5.2. Results of field investigations

Results of the field investigations with pictures and comments are presented in chronological order in this chapter. Each test pit will be described according to the date when sampling was carried out. During the month of June the temperatures were below 10 °C, whereas one month later, temperatures between 25 – 30 °C were noticed. As this was assumed to have an influence the soil samples condition, as well as heavy rainfalls complicating construction works, it appears to be suitable to discuss samples for each test pit in relation to date and climate. Conditions under which sampling took place, information about first impressions, and observations at different levels of depth including possible layers, varying water contents and temperatures as well as special features are presented. A comparison of the analysis carried out in the field laboratory and an evaluation will finally sum up the results of the field works. A number of additional pictures were chosen to show the practical work itself and can be found in Appendix A.

A documentation of the Eastern Suorva dam core 23 5. Documentation of Field Investigation

5.2.1. PG ÖD 650 – Eastern Dam Section 650

The first samples were taken June 29th, 2004. It was cloudy but did not rain during the time samples were taken, and the temperature was around 8 - 10 °C. A first layer of about 15 – 20 cm was scraped away in order to get a plain surface of the moraine core, which seemed to be loosely compacted at this level. This changed as the excavation proceeded downward; compaction appeared to become denser with depth. The first layer had a brown, i.e. oxide colour which changed to grey after the first 10 cm. Several stones at a size of about 30 – 40 cm were found in different places, but no accumulation of such boulders was noticed, see Figure 5.1.

Figure 5.1: PG 650: Surface of the moraine core with example of boulder and oxide coloured material

An overall impression was that the moraine core seemed to be homogeneous, see Figure 5.2.

Figure 5.2: PG 650: Homogeneous moraine core

A documentation of the Eastern Suorva dam core 24 5. Documentation of Field Investigation

No significant changes in colour or water content at different levels were noticed. As the temperature of the material was estimated to be close to the air temperature it was not measured. Sieving confirmed the overall impression of homogeneity. All grain – size distribution curves lie close to each other, see Figure 5.3. The content of fines < 0,06 mm ranges from 29 % to 35 %, the percentage of fraction < 2,00 mm from 75 % to 84 %. Only a slight change between curves from the upper layer between 0,0 m to 0,5 m compared with curves from 1,0 m to 2,0 m depth is noted. The water content ranged from a minimum value of 6,5 % at a depth of 0,5 m to a maximum value of 7,7 % at 2,0 m, the average value of all five samples was 7,0 %. The results of this analysis are summarized in Figure 5.3.

Clay & Silt Sand Gravel 100

90

80

70 0,00m 0,50m 60 1,00m 50 1,50m 2,00m 40 Watercontent: 30 0,00 m: 6,9 % 0,50 m: 6,5 % 20 1,00 m: 6,8 % 1,50 m: 7,3 % 10 2,00 m: 7,7 %

0 60 0,01 0,06 0,1 1 2 10 20 100

Figure 5.3: Analysis of grain-size distribution and water content of samples from PG 650 in field laboratory

A documentation of the Eastern Suorva dam core 25 5. Documentation of Field Investigation

5.2.2. PG ÖD 700 – Eastern Dam Section 700

Soil samples in section 700 on the Eastern Suorva dam were taken on July 1st, 2004. Sampling was planned to be carried out a day before but was delayed because of heavy rainfall. During investigation it was sunny and dry weather with a temperature of about +18 °C. The excavator bucket had been changed to one with teeth, which loosened and mixed the material while excavating. Consequently, the ground surface of the test pit was not plain, see Figure 5.4. Nevertheless, the sides were tolerably even so that visual examination concerning grain-size distribution, different layers or varying water content at different places were still possible to observe.

Figure 5.4: PG 700: Excavation at 1,0 m level. Note effect of the teeth of the excavation bucket. In general, the fill material seemed to have higher water content in comparison to the first examination, i.e. PG ÖD 650, and the ground resembled a slightly layered structure. Parts of the soil, i.e. golf-ball size pieces, were possible to be broken out by hand and kept together due to the water content. However, these pieces could be broken down into fine – grained material between fingers. The ground appeared to be quite cold and a temperature measurement showed a variation from 4,4 to 3,8 °C on surface of the core down to 1,9 °C at a depth of 1,5 m and 1,6 °C at 2,0 m. The analysis of water content strengthened the impression of a higher water content; it was 7,6 % in the upper layer, and was lowest at 1,0 m depth with a number of 6,9 % and highest at 1,5 m with 8,1 %, see Figure 5.6. The average water content was 7,9 %. Because of the hard rainfall the day before one might assume that the increased water content was due to weather conditions. However, as the temperature measurement showed a considerably lower value in comparison to the air temperature, it is believed that this increase is a result of freezing processes.

A documentation of the Eastern Suorva dam core 26 5. Documentation of Field Investigation

Figure 5.5: PG 700: Layered structure at level 1,50 – 2,00 m

The grain-size distribution in Figure 5.6 shows a slightly coarser composition than those taken from section 650. While the fraction of fines <0,06 mm is somewhat similar and ranges from 26 % to 35%, does the fraction of grains < 2,00 mm vary from 63 % to 75 %, which is 10 % less than in section 650.

Clay & Silt Sand Gravel 100

90

80 70 0,00m

60 0,50m 1,00m 50 1,50m 2,00m 40 Watercontent: 30 0,00 m: 7,6 % 20 0,50 m: 7,7 % 1,00 m: 6,9 % 10 1,50 m: 8,1 % 2,00 m: 7,2 % 0 0,06 0,01 0,1 1 2 10 20 60 100

Figure 5.6: Analysis of grain-size distribution and water content of samples from PG 700

A documentation of the Eastern Suorva dam core 27 5. Documentation of Field Investigation

5.2.3. PG ÖD 750 – Eastern Dam Section 750

Tests were taken on July 5th, 2004, on a sunny day with temperatures around 25 °C. In contrast to the test conditions before, it had been warm and dry for several days prior to excavation. The material on top of the core was removed right before excavation of the test pit, which included a layer of boulders and an insulation layer. The excavating bucket had been changed back again, thus a flat and even surface could be examined. Remains from measures against leakage were found, such as standpipes and bentonite which had been used for injection. The amount of stones and boulders found in the upper layer was larger in comparison with that of previous test sites, but may be due to the fact that removal of top layer had taken place right before and left-over material was not scraped away as accurately as it had been in earlier field works.

leftover standpipes

Figure 5.7: PG 750: The surface of the test pit. Note the left-over standpipes from injections as well as stones and boulders.

While the outer layer of fill material was dry and well-graded, it appeared to have an increased moisture content already at an excavation level of 0,4 – 0,5 m. The soil seemed to be completely saturated at this point and water was expelled when pressure was imposed by setting a foot on it, see Figure 5.8. The consistency varied from very soft to an almost liquid state. The water content was found to be extremely high in comparison to previous sampling, even though the weather conditions were much warmer and dryer. It ranged from 11,4 % at level 0,0 m to a maximum of 13,4 % at 0,5 m.

A documentation of the Eastern Suorva dam core 28 5. Documentation of Field Investigation

Figure 5.8: PG 750: Saturated moraine at level 0,4 – 0,5 m. Excess water around footprint.

At a depth of 1,0 m the moisture content changed drastically and was, compared with the earlier situation, quite low at 1,0 m sampling level: 8,4 %. In addition, during examination of the excavated sides of the pit, a 0,5 m long gap was left when a stone of about 20 cm length came out. The surrounding area was wet and appeared to have a low temperature, which was approved by the temperature measurement. The lower values of about 1,7 °C to 1,9 °C in comparison to 3,3 °C in the upper layer and 2,0 °C in the lower layer led to the assumption that the moraine core had been frozen at this level. In general, the moraine core in this section had clearly high water content and had a layered structure at a depth of about 40 – 70 cm, where large parts of soil were able to be taken out as whole blocks. The plastic consistency resulted in some kind of clayey behaviour. The following pictures in Figure 5.9, 5.10 and 5.11 show the situation before and after stones and gravel were removed. At first, horizontal crack is clearly visible, while the following picture shows an accumulation of moisture after the loose material was taken away. The temperature measurement is shown in Figure 5.11.

A documentation of the Eastern Suorva dam core 29 5. Documentation of Field Investigation

fracture

Figure 5.9: PG 750: Wet and layered moraine at level 0,4 – 0,5 m.

loose material

Figure 5.10: PG 750: Wet moraine at level 0,4 – 0,5 m

Figure 5.11: PG 750: Temperature measurement in area with moisture accumulation

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An overall view of the complete side of the test pit is given in Figure 5.12, where the separation in soil colour, water content and structure at level 0,3 – 0,8 m is obvious. The temperature measurement is marked. It may also be noted that the moraine core regarding structure, colour and density looks similar to PG 700 and PG 650 from 0,8 m level down.

temperature measurement ca. 0,3 - 0,8 m

Figure 5.12: Overall view of PG 750. Note the border between material properties at 1,0 m level. The picture was taken at 2,0 m level.

The variation of grain-size distribution in different levels is much larger than that found in other test pits, Figure 5.13. In general, the difference between the curves was found to range from 4 % to 12 %. However, the grain-size distribution of the sample taken at level 2,0 m was much coarser than the samples before; a variation of 16 % - 20 % was found when comparing all five samples of this test pit. It may also be noted that curves of level 0,0 m and 0,5 m are quite similar, as well as curves of 1,0 m and 1,5 m. Due to the fine-grained material, the water content and the low temperature it is assumed that ice lens formation had taken place at that level and that water was generated by thawing processes. The difference between curves from 1,5 m level and 2,0 m level show a similar feature with that of samples from PG 700: The largest fractions were taken from 2,0 m level and the smallest fraction from 1,5 m. One might expect that 0,0 m and 2,0 m samples represented envelopes, and that 1,5 m and 2,0 m correlate. The differences are associated with the comparatively

A documentation of the Eastern Suorva dam core 31 5. Documentation of Field Investigation high water content, thus implicating that fine-grained material is more frost susceptible, and that water is collected preferably in such locations.

Clay & silt Sand Gravel 100

90

80

70 0,00m 60 0,50m 1,00m 50 1,50m 2,00m 40

30 Watercontent:

20 0,00 m: 11,4 % 0,50 m: 13,9 % 10 1,00 m: 8,4 % 1,50 m: 10,4 % 0 20 60 2,00 m: 6,6 % 0,01 0,06 0,1 1 2 10 100

Figure 5.13: Analysis of grain-size distribution and water content of samples from PG 750 in field laboratory

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5.2.4. PG ÖD 200 – Eastern Dam Section 200

Surveying on PG 200 dam was carried out on august, 26th, 2004, almost a month later than the first test pit. Weather conditions were good; it was a dry day with temperatures around 20 °C. The crest was removed right before sampling proceeded in the afternoon. Again, the bucket of the excavator was changed to one with teeth, and the material was loosened and mixed as it was in PG 700. The content of boulder on the surface appeared to be relatively high, but was due to the removal of the upper layer right before. The soil was fine-grained, well-graded and well-distributed at deeper levels. The different curves of grain fractions do not show a special characteristics or variations. Furthermore, the water content did not differ significantly and the temperature did not feel considerably low. A general impression was that this situation was similar to the first examination in PG 650, where it was found that the fill material was homogeneous, see Figure 5.14.

0,30 m

1,00 m

Figure 5.14: Overall view of PG 200. Picture taken at 2,0 m level.

A documentation of the Eastern Suorva dam core 33 5. Documentation of Field Investigation

Only a slightly layered structure was visible at a depth of about 25 cm, see Figure 5.15. No accumulation of special grain-sizes, stones and boulder, or moisture was noticed. The water content was comparatively low in comparison with previous tests, the medium value was 6,92 %.

layered structure

Figure 5.15: PG 200: Layered structure at level 0,25 m.

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The variation of fractions at the different depths was relatively small. All curves in the following diagram are close to each other, and in comparison to the three previous diagrams, the range of particle size distributions is limited and close to original fill material from storage.

Clay & silt Sand Gravel 100

90

80

70 0,00m 0,50m 60 1,00m 50 1,50m 2,00m 40

30 Watercontent:

20 0,00 m: 6,5 % 0,50 m: 7,1 % 1,00 m: 6,8% 10 1,50 m: 7,6 % 2,00 m: 6,6 % 0 0,06 0,01 0,1 1 2 10 20 60 100

Figure 5.16: Analysis of grain-size distribution and water content of samples from PG 200 in field laboratory

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5.3. Comparison and evaluation

5.3.1. Comparison of particle-size distribution

The investigations and the samples taken from the four different test pits were supposed to show if the core of the dam had been exposed to freezing and thawing and if it had been influenced by frost action such as cyclic freezing and thawing. Originally, it was assumed that, in case the grain-size distribution varied significantly, the effect of frost action would be visible in the grain-size distribution when comparing the graphs of samples from the different depths at each site. Particle-size distributions from the archive, i.e. from one section of the Eastern Suorva dam, as well as a graph from the moraine coming from the same storage as currently used material, have been collected. In addition, information from sampling for ongoing construction works, i.e. grain-size distribution from new placement layers and from the moraine pit, was put together. These curves where analysed as to how much they vary, upper and lower limits of percentage were noted to find out a range or an envelope. These graphs can be found in appendix B. However, they will be described in detail in this chapter to provide a basis for comparison and evaluation. The particle-size distributions in Section 741+3,5 and 737 from the year 1983 are taken from records, when leakage was observed and field investigations were carried out. The leakage was considered to be due to internal erosion, which explains the low content of fines in some of the curves. The graphs vary to a large extent and are taken from different depths, so that it is not completely correct to compare the particle-size distributions. Nevertheless, it gives an impression of the material of the core and its variation, and is therefore included in the evaluation. Two graphs in Appendix B, MT 015 – 035, and MT 010 - 018 are taken from the material coming from the moraine pit during construction works in summer 2004. Samples have been taken daily and numbered starting with MT 001. Five samples were collected for each graph for comparison. The black envelope curves show the limits of particle-sizes from the original moraine pit taken from archive documents from 1969. There is no complete correspondence to the original moraine grain-size distribution, almost all graphs lie partly below the lower limit. For sand, the correlation is relatively high; i.e. the graphs are more or less in the range of the envelope. Yet, particles larger than 2 mm generally have a lesser percentage; the material is coarser than that of the archive. Up to this limit, the curves from the fill material from the pit, MT 015 – MT 035 and MT 010 – MT 018, coincide and are homogeneous. This applies also to the fill material which was placed during actual construction works. Layers at different depths, layer one, two and three from section 580 to 680, have a similar particle-size distribution. A placement layer has a thickness of approximately 0,7 m. It is striking that the fractions differ in the diagram for placement layers in sections 225 to 280, since the fill material was exactly the same as for section 580 to

A documentation of the Eastern Suorva dam core 36 5. Documentation of Field Investigation

680 and comes from the same storage. However, the curves show a higher content of gravel. Such an increased fraction of gravel, i.e. a lower percentage of grains < 1 mm to < 2 mm can be noted in samples from PG 650 and PG 200, as well as in PG 700. Particle-size distributions in the region from 0,063 mm to approximately 1 mm are close and show narrow upper and lower limits of percentage. These limits are somewhat extended for larger grain-sizes. Again, as for samples from placement layers, almost all graphs show a larger percentage of gravel than that of the diagram taken from the archive. Table 5.5: Comparison of upper and lower limits in grain-size distribution Test Pit PG ÖD PG ÖD PG ÖD PG ÖD 741 + 3,5 737 Moraine Pit 650 700 750 200 fraction [%] [%] [%] [%] [%] [%] [%] < 0,06 mm min 29,4 26,3 24,4 32,8 23 15 30 < 0,06 mm max 35,4 34,6 44,4 36,8 34 38 48 ∆ max - min 6,0 8,3 20,0 4,0 12 23 18 < 2,00 mm min 74,7 62,6 65,1 73,5 66 72 78 < 2,00 mm max 84,1 74,8 81,1 79,6 89 88 91 ∆ max - min 9,4 12,2 16,0 6,1 23 16 13 < 20,0 mm min 90 84 83 90 100 100 100 < 20,0 mm max 99 98 100 99 100 100 100 ∆ max - min 9,0 14,0 17,0 9,0 0 0 0

The general correlation between the envelope and the fractions of the samples is least in PG 650, where all curves are partly located outside of the envelope at a particle-size > 1 mm, and the 2,0 m curve is completely placed on the outer side. For PG 700, the same applies for three curves, and in PG 200 for all curves > 2 mm. Samples from PG 750 essentially show the largest fine-grain content and correspond to the given limits to a large extend. However, it is noticeable that soil taken from level 2,0 m is outside the lower boundary, which indicates that the fractions are much coarser in comparison to the other four tests. This is similar to PG 650, but the upper and lower boundaries for PG 750 are enlarged; i.e. the grain-sizes vary to a larger extend in different levels. Especially the high water content in PG 750 seems to be connected to the grain-size analysis. Parts of increased water content are associated to fine-grained soil, as the diagram shows for samples from level 0,0 m, 0,5 m, and 1,5 m. The comparatively low water content for 2,0 m matches the graph of coarser fill.

A documentation of the Eastern Suorva dam core 37 5. Documentation of Field Investigation

5.3.2. Evaluation of samples and their grain-size distribution

When comparing the grain-size distributions from sampling, actual construction work and from archive material, there is a relatively large variation. An evaluation of effects of cyclic freezing and thawing on basis of sieving analysis of the samples does not seem to give the expected information. One might expect that the range of grain- sizes shows a similar homogeneity when regarding moraine taken from the pit and moraine used for placement layers, since it is exactly the same material, excavated and transported to the embankment dam within a short time period of a few days, or maybe also a few weeks. Yet, even in the diagram showing placement layers from section 225 to section 280, curves are located mostly outside the given limits and showing some difference between upper and lower limits. This graph can be compared with samples from PG 650 and PG 700. The diagram for PG 200 demonstrates the homogeneity which was observed visually during sampling. Particle-size distributions from the archive taken from section 741 and section 737 vary to a large extend and underline that such diagrams probably are not suitable for a correct evaluation in terms of frost action and effects on the core of the embankment dam. In order to be able to draw a conclusion about frost action, visual inspection, pictures, as well as measurements of water content and temperature seem to be much more significant in comparison to the sieving analysis. As the water content was exceptionally high in some places, and the temperatures at the same time low compared to the air temperatures, it was likely that the soil had been frozen. A comparison of these values is given in Table 5.5. Table 5.6: Comparison of water content values and temperatures Test Pit PG ÖD 650 PG ÖD 700 PG ÖD 750 PG ÖD 200 Level w [%] w [%] Temp [°C] w [%] Temp [°C] w [%] 0,0 m 6,9 7,6 4,4 - 3,8 11,4 3,3 6,5 0,5 m 6,5 7,7 - 13,9 1,9 - 1,7 7,1 1,0 m 6,8 6,9 2,3 - 2,1 8,4 2,0 6,8 1,5 m 7,3 8,1 1,9 10,4 1,6 7,6 2,0 m 7,7 7,2 1,6 6,6 1,3 6,6 ∅ 7,04 7,50 10,14 6,92

Especially in PG 750, where the soil was saturated and the temperatures were about 1,7 °C to 3,3 °C, it is believed that ice lens formation had been taking place. Other observations such as a layered structure were made in almost all test pits, mostly at depths between approximately 0,3 m to 0,8 m. Nevertheless, evidence for effects of frost action, such as changes in structure, density, volume, permeability or particle movements is not given. Tests about the original density and permeability, as well as different graphs of varying nature in grain-size distribution are not available. Therefore, a sufficient basis for evaluation of the observations is missing.

A documentation of the Eastern Suorva dam core 38 5. Documentation of Field Investigation

5.3.3. Limitations in sampling and discussion

There are various factors influencing the collection of samples, thereby also affecting the outcome of the result. First of all, the short summer up in the mountains limits the period for construction works, so that the time for sampling is also restricted. In addition, hard rain during the month of July made it impossible to proceed with earthworks. Investigations in test pits could probably have been carried with more accuracy if the time pressure had been less. Another problem is that sampling did not occur under similar circumstances; changing weather conditions or different excavation buckets affect the quality of the soil samples. The removal of material which covered the core was done right before sampling the same day, or some days before, thereby exposing the fill material to the surrounding climate. While the first samples were taken in June, where temperatures in the air were below 10 °C, the last samples were taken in the end of August, which represents almost the end of the summer period in this region, and temperatures had temporarily risen up till 25 °C. Thus, warmer temperatures had been able to proceed downward into the ground. A comparison of soil temperatures of different test pits does not seem suitable and was therefore only carried out in PG 700 and PG 750 as sampling took place during a short time period under similar conditions.

A documentation of the Eastern Suorva dam core 39 6. Thermal analysis

6. Thermal analysis

6.1. Introduction

The question about whether or not temperatures below the freezing point affect the core of the embankment dam cannot be answered by the results of the field investigations and laboratory tests. Since effects such as volume changes, changes in void ratio, cracks, particle movements or redistribution of grains have been observed in similar soils exposed to freeze and thaw (Viklander 1997), it has to be considered that frost can penetrate into the dam, influencing or reducing the functions of different parts of the structure. The mentioned effects can decrease considerably the function of the core as hydraulic barrier, and freezing conditions in the filter zones possibly may lead to serious drainage problems. In order to get an impression of the temperature distribution in the construction, a thermal analysis was carried out. Modeling and calculation of thermal changes was carried out with the help of the finite element program Temp/W. The Swedish Meteorological Institute SMHI provided temperature records measured at the meteorological station in Stora Sjöfallet, 10 km east from the Suorva dam. To be able to compare the results of the thermal analysis with observations from field investigations, the temperatures during 2002, 2003 and 2004 where regarded as relevant for the outcome of the calculations. Detailed information about the temperature records can be found in Appendix C. Two different situations are regarded in the calculations. The first construction displays a complete dam crest, while the second construction presents the actual situation in the sections 650, 700, and 750, where the crest was not completely rebuilt after repair work due to internal erosion in 1983. The crest cap was missing a regular cover of rock fill or rip rap, and a layer of 5 cm thick insulation was placed on top of the core, which was kept in place by some rock fill material.

A documentation of the Eastern Suorva dam core 40 6. Thermal analysis

6.2. Definition of the problem

6.2.1. Drawing the problem

The problem is drawn and defined by the function Temp/W Define. This basic part of the program provides a CAD-similar function to sketch the problem, develop a mesh of finite elements and define material properties. One of the several different cross-sections of the embankment dam (which vary mainly in height because of the varying foundation levels) was chosen and information about water levels and air temperatures were collected. For the drawing of the embankment dam the cross-section of section 400 was used as basis. The original drawing from the archive is shown in Figure 6.1. In the basic drawing in Figure 6.2, the construction is 44 m high at this section and has a maximum width of 120 m. The core is sloped at water side and placed between filter zones.

Figure 6.1: Drawing from the archive used for sketching the problem

Since the water level is varying by time and the mesh cannot be changed during the computation of the problem, a medium water level was used. This is essential for the following definition of material properties in different zones and unsaturated and saturated condition, as the thermal properties are substantially dependent on the water content. A value of 440 m above sea level was calculated as average value of the maximum water levels during the years 2002 to 2004. The seepage level throughout the whole construction should have been calculated in order to get a more exact border line for material properties. However, as the actual seepage condition is only a presumption based on a medium value, and is mainly supposed to

A documentation of the Eastern Suorva dam core 41 6. Thermal analysis show the influence of the water temperature in general, seepage was simplified and approximated by straight lines.

Figure 6.2: Basic drawing of the problem

To generate finite elements, a mesh was drawn, consisting of 2214 elements and 2384 nodes. The elements have different side length, varying from 0,5 m in the upper zone up to + 446 m above sea level, 1,0 m between + 446 m to 443 m and 2,0 m down to the foundation. Since the area of the cross section of the embankment is quite large, the element size was increased at lower levels to avoid a too large number of nodes and mistakes in the verification and sorting of the elements. All elements are quadrilateral elements with four nodes and nine-point integration order. The parameters are defined in a toolbox shown in Figure 6.3.

Figure 6.3: Toolbox for drawing multiple elements

A documentation of the Eastern Suorva dam core 42 6. Thermal analysis

6.2.2. Specification of functions and analysis type

After sketching the problem, several functions, material properties as well as specifications of analysis type and convergence are needed to actually be able to calculate a temperature distribution. The different steps for input of data are explained in this section. The type of analysis can be changed from steady-state to transient analysis. For the computation of an initial condition, the steady-state function is chosen. The following analysis which is based on temperature functions requires time increments and temperature functions; therefore, transient has to be chosen after obtaining a suitable initial condition to base upon. Since the elements have a nine-point integration order, the convergence criteria toolbox ‘KeyIn Convergence’ is used to set a multiple of the number nine for the Gauss Region/Iteration, see Figure 6.4. The Gauss Region/Iteration (GRI) controls the rate at which a region of phase change is established. It is suggested to use a multiple of the integration order shown in Figure 6.3 to acquire a more uniform freeze/thaw interface. Values from 9 to 45 can be chosen. A high value usually is applied in problems which are expected to show a mainly vertical frost front movement as there is a large number of Gauss iteration regions at one level. This is not the case for the given problem, but the resulting temperature distributions were similar when using the minimum number of 9 and the maximum of 45. It was therefore decided to run all computations with the value of 45.

Figure 6.4: Toolboxes for analysis control and convergence criteria

A documentation of the Eastern Suorva dam core 43 6. Thermal analysis

6.3. Material properties

6.3.1. In general

When finite elements are drawn as multiple elements, the program asks for material properties for the elements. The volumetric heat capacities in frozen and unfrozen state as well as the volumetric water content are values which have to be set in the toolbox. Furthermore, links to temperature dependent functions of unfrozen water content and conductivity are defined. Information for the properties of moraine was taken from the soil samples. The water content is a medium value of all the test pit samples; yet, the samples from test pit 750 where left out since the water content in this case was increased to an extent which did not seem to be suitable for an average value. In the context of construction works, permeability tests on new soil samples where carried out at the university laboratory. It therefore was possible to obtain values for density of the material. The different zones in the embankment dam show varying thermal properties. Porosity, water content and saturation diverge. Since there where no samples from filter zones and rock fill analyzed, realistic and suitable values were chosen after personal communication. The values used for calculation are summarized in Table 6.1.

Table 6.1: Material properties used for calculation of thermal properties

Moraine Filter Supporting fill

unsaturated saturated unsaturated saturated unsaturated saturated (1) (2) (3) (4) (5) (6) Water w [%] 7.20 10.3 4.0 15.0 3.0 20.0 content ρ Dry density d 2.13 2.13 1.91 1.91 1.75 1.75 [t/m3] Bulk ρ 2.28 2.35 1.99 2.20 1.80 2.10 density [t/m3] Grain ρ s 2.73 2.73 2.70 2.70 2.70 2.70 density [t/m3] Porosity n [-] 0.22 0.22 0.29 0.29 0.35 0.35

Void ratio e [-] 0.28 0.28 0.41 0.41 0.54 0.54 Degree of S [%] 0.070 1.0 0.026 1.0 0.015 1.0 saturation r Volumetric Θ = water n * Sr 0.02 0.22 0.01 0.29 0.01 0.35 content [%]

A documentation of the Eastern Suorva dam core 44 6. Thermal analysis

6.3.2. Heat transfer processes

As explained in connection with climate and the grounds thermal regime, thermal energy can be transferred in different ways. The processes of conduction and convection are most important when regarding the heat transfer in soils. Since radiation depends on a number of factors as described in the section above, and therefore is hard to measure, it is usually not taken into account in engineering applications. However, tools are available for taking radiation into consideration. (Hermansson, 2002)

6.3.2.1. Conduction and convection

Energy passing from particle to particle is called conduction. This form of heat flow is independent of mass and it moves in direction from higher to lower temperatures. The heat flow transmitted by a material under a given temperature gradient is a characteristic property and is defined by the thermal conductivity. In materials with voids filled with water or ice, the predominant mechanism for the heat transfer is conduction. Heat transfer via convection is dependent on mass transfer, i.e. movement of heated molecules. Convection takes place in soil when pore water, air or gas is moving through interconnected pore spaces. Convection can also be connected to the transport of thermal energy during thawing progress. Liberated water is redistributed in upward direction because of the lower region which is still frozen. The magnitude of the thermal gradient and the temperature at ground surface is reduced by this process. [Andersland and Anderson, 1978] Above the ground surface, important convective energy losses are due to wind and its velocity. [Hermansson, 2002]

6.3.3. Thermal properties of soils

The thermal properties of soils describe the ability for heat transmittance. These properties have to be known in order to be able to calculate the frost or thaw depth. The decisive properties are heat capacity, thermal conductivity, and latent heat. They are not constant, but vary to some extent according to temperature, type of soil, water or ice content, saturation, and soil density. As these properties are needed for the following thermal analysis, an overview will be given in this section.

A documentation of the Eastern Suorva dam core 45 6. Thermal analysis

6.3.3.1. Latent heat

Upon freezing or thawing, water is transformed from liquid to solid state, or inverse from solid to liquid state. This phase change requires an amount of heat which has to be either removed or provided. Latent heat L is absorbed or liberated during phase change, but does not change the temperature. Water itself has a latent heat of 333 J/g. For soils, the latent heat has to be calculated, as it is composed of grains, water, and air. The energy needed for the process of freezing or thawing depends on the moisture content of the soil and the amount of water changing the phase. This energy amount is called effective latent heat.

The effective latent heat L’ can be calculated dependent on the soils dry density ρd and its water content w:

L'= ρ d ⋅ w ⋅ L [J/m³] (6.1)

6.3.3.2. Specific heat capacity

The required amount of heat to raise the temperature of 1 kg of a given material by 1 °C is called heat capacity. The specific heat capacity c is based on the unit weight and expressed in [kJ/kg*K]. The volumetric heat capacity C is based on the unit volume and expressed in [kJ/m³*K]. For a composite material such as soil, the different heat capacities of the constituents- solid, ice, water and air- can be added according to their respective weight fraction. For determination of frost depth the specific heat on volumetric basis is used and, for unfrozen soil, calculated by

C = ρ d ()cs + w⋅ cw [kJ/m³ * °C] (6.2)

where ρd stands for dry density, cs for specific heat capacity of the particles, cw for specific heat capacity of unfrozen water, and w for water content. If in a frozen soil all water is frozen, the equation has to be adjusted and a value for cw has to be exchanged by a value for cice. Values used for calculations are shown in Table 6.2.

Table 6.2: Values for the specific heat capacity c

Solid particles cs 0,75 [J/g* °C]

Water, liquid cw 4,2 [J/g* °C] Water, ice cice 2,0 [J/g* °C]

A documentation of the Eastern Suorva dam core 46 6. Thermal analysis

6.3.3.3. Thermal conductivity

The thermal conductivity λ characterizes a material in its ability to transmit thermal energy by conduction. It is defined as the amount of heat flow through a unit area under a unit time and a temperature gradient of 1 °C. The thermal conductivity is calculated by

Q λ = [W/m*K] (6.3) A⋅ ()T1 − T2 L

Q represents the heat flow, A the cross-section area, T1-T2 the temperature difference, and L the latent heat.

Soil particles, water, ice and air have different values of thermal conductivity. The overall conductivity of a volume of soil has to be calculated according to the presence of the different soil constituents. Ice can transmit four times more heat than water; consequently, frozen soil has a higher thermal conductivity than unfrozen soil. The density of grains, water content and the porosity, as well as the state of pore water determines the over-all thermal conductivity. For calculations of thermal conductivity of a soil, the porosity and the water content has to be known. With this value, λ for a soil containing n parts of water and (n-1) parts of solids can be determined by the equation

λ = (λsat − λdry )⋅ K + λdry [W/m*K] (6.4)

In order to find the value of λ from equation (6.4), the thermal conductivity of the saturated soil, λsat, and of the dry soil λdry has to be calculated separately. This can be carried out by taking the thermal conductivity of the particles, λparticle, of water, λwater, and of ice, λice, into consideration. Further, the porosity n has to be known.

(1−n) ()n λsat = λ particle ⋅ λwater [W/m*K] (6.5)

−2,1 λdry = 0,036 ⋅ n [W/m*K] (6.6)

A documentation of the Eastern Suorva dam core 47 6. Thermal analysis

Kerstens number, the factor K in equation (6.4) depends on the degree of saturation

Sr and the state of water. For all kinds of frozen soils, i.e. for soils having temperatures below 0 °C, K is determined by:

K = Sr (6.7)

For temperatures above zero, a distinction is made between coarse-grained and fine- grained soils:

K = ()0,7 ⋅ log Sr +1 (Coarse-grained) (6.8)

K = log Sr +1 (Fine-grained) (6.9)

Typical values for thermal conductivity used in following calculations are summarized in Table 6.3.

Table 6.3: Values for thermal conductivity λ

Solid particles λs 3,8 [W/m*K]

Water, unfrozen λuf 0,6 [W/m*K] Water, frozen λf 2,2 [W/m*K]

A documentation of the Eastern Suorva dam core 48 6. Thermal analysis

6.3.4. Material data for computation

In order to be able to assign thermal properties of the different layers of the embankment dam, several calculations have to be carried out. These calculations are based on the equations which are explained above. The results for the thermal conductivity λ of different materials are summed up in Table 6.4.

Table 6.4: Summary of the results of the thermal conductivity for different materials Moraine Filter Rock fill insulation unsaturated saturated unsaturated saturated unsaturated saturated

T < 0°C: λsat 3.37 3.37 3.24 3.24 3.14 3.14 /

T > 0°C: λsat 2.53 2.53 2.22 2.22 1.99 1.99 /

λdry 0.87 0.87 0.48 0.48 0.33 0.33 / T<0°C: K 0.068 1.0 0.026 1.0 0.015 1.0 / T>0°C: K -0.170 1.0 -0.110 1.0 -0.277 1.0 /

λice (T<0°C) 1.0357 3.3695 0.5562 3.2430 0.3686 3.1384 0.03

λuf (T>0°C) 0.5821 2.5318 0.2930 2.2249 0.0000 1.9916 0.03

∗λice (T<0°C) 89.48 291.12 48.05 280.20 31.85 271.16 2.59

∗λuf (T>0°C) 50.29 218.75 25.32 192.23 0.00 172.08 2.59 (*The grey marked values are used to run the program Temp/W. Since the time steps are calculated in days, the numbers have to be adjusted: they are multiplied by 3,6*24)

The volumetric heat capacity C is calculated according to Equation (6.2), using the values in table for the specific heat capacity in Table 6.2. The results used for analysis are shown in Table 6.5:

Table 6.5: Values for volumetric heat capacity Moraine Filter Rock fill insulation unsaturated saturated unsaturated saturated unsaturated saturated

Cice (T < 0°C) 1904.22 2036.28 1585.3 2005.5 1417.5 2012.5 160

Cw (T > 0°C) 2241.612 2518.938 1753.38 2635.8 1533.0 2782.5 160

A documentation of the Eastern Suorva dam core 49 6. Thermal analysis

These properties are necessary to define for each ‘material’. The program gives each material a number which is used by the program. The toolbox for defining the material properties is shown in the following Figure 6.5.

Figure 6.5: Input of thermal properties for the different materials

6.3.5. Temperature function

As mentioned in the introduction of the thermal analysis, temperature records from the Swedish Meteorological an Hydrological Institute SMHI where applied for the computation. Five-day mean temperatures where calculated for the time periods winter 2002/2003, summer 2003, and winter 2003/2004. These five-day mean temperatures provide a function for the transient analysis for each season, see Figure 6.6. A winter period includes the months of November until April, while a summer period runs from May until October. This results in 36 time steps or 36 five- day mean temperatures for winter and 37 steps for summer.

A documentation of the Eastern Suorva dam core 50 6. Thermal analysis

Figure 6.6: Example of an air temperature function used as boundary condition

6.4. Solving the problem

When the problem is drawn and the different material properties, boundary functions, time increments etc are defined, the problem can be calculated by using the function Temp/W Solve. For computation of the initial condition, the analysis type has to be set to steady-state. For the further analysis, the matching initial condition file based on the previous calculation has to be chosen in order to guarantee that the following computation is based on the right temperature distribution. When the problem is solved, the result can be viewed by the function Temp/W Contour which generates contour plots of the temperature distribution. The temperature distribution is easily visible and the line of the freeze-thaw interface is drawn. This function was used to present the results of the analysis in the following section.

A documentation of the Eastern Suorva dam core 51 6. Thermal analysis

6.5. Steady-state analysis an boundary conditions

The temperature which influences the whole construction most is that of the steady- state analysis. This temperature distribution is responsible for the following calculation as it governs the amount of heat energy stored in the body of the embankment dam. It was therefore chosen to base this initial calculation on the annual mean temperature, which, according to SMHIs records for a thirty-year mean value, is about -1,0 °C (see Figure 3.3). It has been observed that the annual mean temperature increased slightly during the last five years (ranging from -1,0 °C up to +2,5 °C) , and the last four winters have been exceptionally warm in comparison. Therefore, two different calculations have been carried out, one with an annual mean temperature of -1,0 °C, and one with an increased annual mean temperature of -0,4 °C.

The temperature distribution inside the body of the embankment dam is also dependent on the water table and the seepage through the construction. However, information about seepage and water temperatures is not available. With regard to the special property of water having its highest density at +4,0 °C, a boundary condition of +4,0 °C was used for the summer period, whereas a linear distribution from +1,0 °C to +4,0 °C from top to bottom was chosen for winter conditions.

A documentation of the Eastern Suorva dam core 52 6. Thermal analysis

6.6. Results of the thermal analysis

6.6.1. Results for a construction with complete dam crest

The calculation was carried out twice, based on the different mean annual temperatures measured over a thirty-year period. The boundary condition of an annual mean temperature of -1,0 °C applied for the computation of an initial condition resulted in the temperature distribution shown in Figure 6.7:

Figure 6.7: Initial condition based on a boundary condition of -1 °C.

The temperature distribution differs according to the applied boundary conditions. Temperatures below zero around the dam crest, the left side and the right side above water level are due to the air temperature of -1,0 °C. The right side below the water table is exposed to the water temperature which was assumed to be +4,0 °C. The arrows around the marked water table show the direction of heat flow. Based on this condition, temperature functions for the three following seasons, i.e. winter 2002/2003, summer 2003 and winter 2003/2004 where applied. It is noted that the line of the freeze-thaw intercept, which is drawn in blue colour, does not move significantly in comparison to the initial condition. Only the temperatures above, which depend mainly on the boundary function using five-day mean temperatures from the winter 2003/2004, become lower. Figure 6.8 presents the situation at the last time increment, i.e. at the end of April 2004. The grid displayed in the figure has a side-length of two meters, so that a frost depth of approximately 5 m can be estimated in the core of the embankment dam. In addition, the upper filter zones are influenced by these freezing conditions.

A documentation of the Eastern Suorva dam core 53 6. Thermal analysis

Figure 6.8: Final condition at the end of April 2004 based on an initial condition of an annual mean temperature of -1 °C.

When an annual mean temperature of -0,4 °C is applied, the temperature regime inside the body of the dam is displayed as in Figure 6.9. The frost front does not proceed as deep down towards the central core as it does in case of an annual mean temperature of -1,0 °C, but remains in the upper part of rock fill.

Figure 6.9: Initial condition based on a boundary condition of -0,4 °C.

A documentation of the Eastern Suorva dam core 54 6. Thermal analysis

The further calculation with an annual mean temperature of -0,4 °C as initial condition results in a temperature distribution shown in the figure displayed below. It is noted that the freezing front, indicated by the blue line, is located at about a depth of one meter inside the core. A difference of about four meters in frost depth inside of the core can be noted in comparison to the previous calculation based on -1,0 °C for mean annual temperature, but it has to be noted that the freezing font still moves down and affects the core and the filter zones, as Figure 6.10 shows.

Figure 6.10: Final condition at the end of April 2004 based on an initial condition of an annual mean temperature of -0,4 °C.

A documentation of the Eastern Suorva dam core 55 6. Thermal analysis

6.6.2. Results for a construction without dam crest

Since the crest of the dam was removed and not restored completely, the mesh for calculation was modified and a part of the rock fill cover was taken away. The layer on top of the core was estimated to be around 1 m thick, and a layer of insulation between rock fill and core was defined. Again, the calculation was first carried out using the initial condition in Figure 6.11 with a mean annual temperature of -1,0 °C

Figure 6.11: Initial condition based on a boundary condition of -1,0 °C.

After further application of five-day mean temperatures for the following time period, the computation showed a possible frost depth of about 6 m down in the hydraulic barrier of the embankment dam, see Figure 6.12. Important parts of the filter zones are located in the freezing area, which implies that fundamental functions of these parts in the dam may be affected and decreased.

A documentation of the Eastern Suorva dam core 56 6. Thermal analysis

Figure 6.12: Final condition at the end of April 2004 based on an initial condition of an annual mean temperature of -1 °C.

An annual mean temperature of -0,4 °C leads to an advance of the freezing front to the top of the impervious earth fill. Similar to the situation with a complete dam crest, the difference in frost depth is clearly visible, but it can still be noted that freezing temperatures have an impact on the core already in the initial condition, see Figure 6.13.

Figure 6.13: Initial condition based on a boundary condition of -0,4 °C.

A documentation of the Eastern Suorva dam core 57 6. Thermal analysis

After computing the situation with temperature functions from 2002 to 2004, the last time increment at the end of April, 2004 shows the following temperature distribution, Figure 6.14. With the help of the grid the frost depth can be estimated to a 3 - 4 m depth in the central core, i.e. upper parts of the hydraulic barrier as well as filter zones are influenced by freezing conditions.

Figure 6.14: Final condition at the end of April 2004 based on an initial condition of an annual mean temperature of -0,4 °C.

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6.7. Summary and discussion

The calculation of a temperature distribution inside of the embankment dam with the help of the finite element program Temp/W was performed in order to find out and present if and to which extend freezing conditions effect the earth fill in the central core. Two situations were analyzed, one with a complete dam crest, and one with a cover of insulation hold in place with some rock fill material after repair work. To be able to show and compute these two situations, the mesh of finite elements was modified. In addition, since it was observed that the values for the 30-year mean temperature for an annual value became slightly warmer, two different annual mean temperatures ( -1,0 °C and -0,4 °C) were used to find initial conditions as basis for further calculations. I was found that already in the initial condition, the central core was affected by temperatures below 0 °C. The frost line was located at a 4 m to 5 m depth in case of an annual mean temperature of -1,0 °C in both cases with and without dam crest. The frost front proceeded only to the middle of the rock fill above the core or right to the upper level of the core when a mean value of -0,4 °C was used as basis. Nevertheless, in all calculations, both with complete and provisional dam crest, as well as warmer and colder annual mean temperatures did the freezing plane advance to the hydraulic barrier. With regard to wind conditions, which have not been included in these calculations, it is assumed that the freezing plane advances even deeper down in the central core. The water table, which tends to be lower during winter time, reduces the possibility to warm up the inner part of the dam because of seepage, as water passing through the dam during winter has a comparatively warmer temperature than the air. Because of wind does snow usually not cover the embankment dam. Snow can act as insulation for ground in general. This factor can also increase the frost front advance. As can be seen from the calculations, it is not only the central core which is affected by freezing, but also the filter zones. If the freezing plane is located at a larger depth, this situation has to be considered and investigated further in order to assure that both the core and the filter zones meet their requirements.

A documentation of the Eastern Suorva dam core 59 7. Conclusions

7. Conclusions

This MSc thesis was carried out in order to analyze the effect of freezing and thawing in the moraine core of the Eastern Suorva dam. Two different methods are applied. A practical part includes field investigations. For this purpose, test pits were excavated and visually inspected. Samples collected during these investigations were analyzed. Grain-size distributions as well as water contents are compared. In addition, a theoretical part of a thermal analysis using the finite element method completes this thesis.

The field investigations showed that the core of the dam actually is exposed to freezing; layered structures, water content and temperatures of the moraine core give evidence for frost actions. The soil displayed different formations: it appeared partly to be homogeneous, well-graded and dry, while other tests showed that the water content was comparatively high and the soils temperature pointed at being close to the freezing point. A comparison of water content and temperatures gives evidence for freezing of the core.

However, it is not possible to draw conclusions about how these freezing actions affect the core. Detailed information about porosity, void ratio and permeability is needed in order to be able to compare the condition of the core today with the condition right after construction. A thorough analysis of these properties would be necessary.

Thermal modeling with the finite element program Temp/W gives additional evidence that the hydraulic barrier of the dam is exposed to freezing and thawing. It is shown in different calculations that the frost front advances considerably into the core. Freezing does even occur in filter zones. Again, these calculations show the fact that frost action has to be considered. Nevertheless, the question about how this influences the moraine core cannot be answered.

A documentation of the Eastern Suorva dam core 60 8. References

8. References

Alexandersson, Hans, Karlström, Carla, and Larsson-McCann, Sonja (1991) Temperaturen och nederbörden I Sverige 1961-90. Referensnormaler. SMHI Meteorologi Klimatsektionen. Nr. 81, 1991. ISSN:0283-7730 (In Swedish)

Andersland, Orlando B., and Landanyi, Branko (1996). An introduction to frozen ground engineering. London: Chapman & Hall. ISBN 0-412-98201-3

Andersland, Orlando B., and Anderson, Duwayne M. (1978). Geotechnical engineering for cold regions. USA: McGraw-Hill Inc. ISBN 0-07-001615-1

Fell, Robin, MacGregor, Patric, and Stapledon, David (1992) Geotechnical engineering of embankment dams. Rotterdam: A. A. Balkema. ISBN 90-5410-128-8

Hassi, Juhani, et al. (2002) Handbok för kallt arbete. Stockholm: Arbetslivinstitutet. ISBN 91-7045-626-7 (In Swedish)

Hermansson, Åke (2002). Modeling of frost heave and surface temperatures in roads. Department of Civil and Mining Engineering, Division of Soil Mechanics. Doctoral thesis 2002:13, Luleå University of Technology. ISSN 1402-1544

Johansson, Sam (1997) Seepage monitoring in embankment dams. Department of Civil and Environmental Engineering, Division of Hydraulic Engineering. Doctoral thesis 1997, Stockholm Royal Institute of Technology. ISBN 91-7170-792-1

Nilsson, Tore (1972). Fyra gånger Suorva. Stockholm: Statens Vattenfallsverk. ISBN 91-7186-006-1 (In Swedish)

Mill, Olle, and Brandesten, Claes-Olof (2001) Flying the flag for safer dams International Water Power & Dam Construction, June 2001, p.39

A documentation of the Eastern Suorva dam core 61 8. References

Kjærnsli, Björn, Vakstad, Tore and Hög, Kaare (1992) Rockfill dams. Design and construction. Norwegian Institute of Technology, Division of Hydraulic Engineering. Trondheim. Hydropower Development, Vol.10. ISBN 82-7598-014-3

Knutsson, Sven (1981) Tjälningsprocessen och beräkning av tjäldjup. Department of Civil and Mining Engineering, Division of Soil Mechanics. Compendium 99:03, Luleå University of Technology. (In Swedish)

Knutsson, Sven (2004) Personal communication. (December 2004)

Phukan, Arvind (1985) Frozen ground engineering Englewood Cliffs, New Jersey: Prentice Hall. ISBN 0-13-330705-0

RIDAS (2004) Kraftföretagens riktlinjer för damsäkerhet.

Vattenfall (1988) Jord- och Stenfyllningsdammar. Vattenfall, Stockholm. ISBN 91-7186-271-4 (In Swedish)

Viklander, Peter (1997) Compaction and thaw deformation of frozen soil. Permeability and structural effects due to freezing and thawing. Department of Civil and Mining Engineering, Division of Soil Mechanics. Doctoral thesis 1997:22, Luleå University of Technology. ISSN 1402-1544

Viklander, Peter, and Eigenbrod, Dieter (2000) Stone movements and permeability changes in till caused by freezing and thawing. Cold Regions Science and Technology, 31 (2000), pp. 151-162

Taesler, Roger (1972) Klimatdata för Sverige. Stockholm: K L Beckmans Tryckerier. ISBN 91-540-2012-3 (In Swedish)

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