Sweden has more than 190 large hydropower dams, of which about 50 are pure embankment dams and over 100 are concrete/embankment dams. This paper presents results from conceptual analyses of the response of typical Swedish rock mass to the construction of a hydropower embankment dam and its first stages of operation. The aim is to identify locations and magnitudes of displacements that are occurring in the rock foundation and grout curtain after construction of the dam, the first filling of its water reservoir, and after one seasonal variation of the water table. Coupled hydro-mechanical analysis was conducted using the two-dimensional distinct element program UDEC. Series of the simulations have been performed and the results show that the first filling of the reservoir and variation of water table induce largest magnitudes of displacement, with the greatest values obtained from the two models with high differential horizontal stresses and smallest spacing of sub-vertical fractures. These results may help identifying the condition of the dam foundation and contribute to the development of proper maintenance measures, which guarantee the safety and functionality of the dam. Additionally, newly developed dams may use these results for the estimation of the possible response of the rock foundation to the construction

In Sweden there are about 190 large hydropower dams of varying age. According to the definition by the International Commission of Large Dams (ICOLD), if the height of the dam exceeds 15 m it is referred as large. Majority of these dams are of embankment type. The peak of the dam construction in Sweden was between 1950 and 1980, hence, the major part of the dams are between 30 and 60 years old. It is well known that the strength of dam body and foundation rock deteriorates with time. For this reason there are ongoing concerns for the hydropower industry regarding the production and safety of the dams. Currently, the majority of research efforts are concentrated on degradation of hydropower dams whereas less attention is paid to the bedrock under the dam, which is a critical factor for construction integrity and functionality.This work is focused on:1. Better understanding of the rock mass response to the loads caused by construction and exploitation of a hydropower dam, i.e. the loads from the weight of the dam and the water in the reservoir;2. Validation of the developed conceptual model on the case study; 3. Investigation of how static and cyclic loads of the hydropower dam effect the fracture erosion and rock mass stability and grout curtain based on case study (in long-term perspective). An extensive literature review of this field is performed. Based on it a series of factors are selected which are important in terms of opening and shearing along geological structures under dams and reservoirs. Developed conceptual model together with numerical code UDEC (2D) helped to identify the most significant (stress conditions, structural geology and properties of discontinuities) conditions of the rock. The construction of a dam on rock foundation (with its water reservoir) causes redistribution of the stress field, and affects the state of mechanical and hydro-geological properties of the rock mass beneath the dam. The combination of sub-horizontal discontinuities (bankning discontinuities) with sub-vertical discontinuities, which are perpendicular to the river valley, give rise to a water leakage under the dam. This behavior depends on the direction of the dip angle of the sub-horizontal discontinuities, either downstream or upstream. The adverse effect is caused by downstream direction. Magnitude and direction of the in-situ stress field, density of discontinuities, and friction angle of joints are also major factors which affect the behavior of the rock mass considerably. All these findings are in good agreement with the results of other authors. As the developed numerical model showed good agreement with previous research it was adopted for a case study. Håckren dam (Sweden) had been selected for this purpose. A series of field (mapping, RMR, Q, GSI) and laboratory tests (Bulk density, Porosity, Water content, Point Load Strength index) were applied. Results of numerical models showed a good agreement with monitored leakage into the inspection gallery. The deformations within the foundation rock mass has not been monitored therefore numerical results has been evaluated based on the literature review. Results from the numerical models in terms of shear and normal deformations (openings) in the bedrock did not show significant deformations (around 1 mm for shear deformation and less than 0.1 mm in case of opening). Cyclic loading of the water in the reservoir results in accumulation of the deformations within the rock mass. Such processes may create favorable conditions for development of erosion within the bedrock. Numerical results showed an increase of accumulated shear deformations within the rock mass within the first years but then it stabilized. These deformations are occurring along subhorizontal discontinuities in downstream side of the dam and along intermediate joints on the upstream side. The magnitude of opening of the discontinuities is staying low, less than 0.3mm. The inflow into the inspection tunnel increased only during the first years, and then stabilized. However the flow velocity around the inspection tunnel showed a small increase along several simulated years. Numerical simulations showed the stability of the foundation rock of the Håckren dam after construction and within 10 idealized years of the exploitation of the dam. The used approached showed its validity and applicability for preliminary evaluation of the foundation rock of the embankment dams, based on the Håckren dam case.

Det finns över 190 kraftverks- och regleringsdammar i Sverige. De flesta dammarna färdigställdes från år 1950 – 1980 och de har nu varit i drift mellan 30 och 60 år. Tid har en dokumenterat negativ effekt på en damms prestanda. Varierande belastningar från vattenreservoaren under drift kan orsaka små förskjutningar av berggrundens sprickzoner. Dessa rörelser bidrar till nedbrytning av dammen och dess reservoar. Ett ökat vattenläckage och en förändrad portrycksfördelning kan leda till initiering av sprickerosion i berggrunden.Det är viktigt att öka förståelsen om berggrundens stabilitet, dess hydrogeologiska egenskaper och respons på belastningar från dammen ur olika tidsperspektiv. Ett angeläget arbete för svensk vattenkraftindustri är att säkerställa de åldrande dammarnas funktion och säkerhet. För att uppdatera och säkerställa det stora antalet dammar enligt nya beräknings- och bedömningsmodeller samt ändrade förutsättningar kommer många dammar att behöva uppdateras, och åtgärdas för att öka dess säkerhet, varför kraftindustrin framöver kommer att göra mycket stora investeringar.Syftet med denna doktorsavhandling är att studera vilka konsekvenser varierande belastningar från damm och reservoar har på berggrundens stabilitet och dess sprickerosion. Jag använder den kopplade hydromekaniska distinkt-element metoden UDEC [Itasca, 2005]. Små förskjutningar längs berggrundens sprickor har studerats över lång tid tillsammans med portrycksfördelning, vattenläckage och vattenflödeshastighet. De numeriska modellerna har en verklig damm som förebild med platsspecifika indata, nämligen Håckren fyllningsdamm i centrala Sverige.Två vinkelräta konceptuella modeller i 2D har utvecklats [Bondarchuk, 2008]. Berggrundens normal- och skjuvförskjutningar analyserades. Resultaten visar att sub-horisontella och subvertikala strukturer kan samverka och ge upphov till vattenläckage under dammen. Beteendet beror på bankningsplanens stupningsriktning. Sprickfrekvensen och de primära spänningarnas storlek och riktning är andra viktiga faktorer för berggrundens beteende.De två konceptuella modellerna har anpassats till en verklig dam genom att använda så mycket platsspecifik data som möjligt. Ny data samlades in med hjälp av vanlig förekommande ingenjörsgeologiska metoder. En god överensstämmelse mellan modellresultat och övervakningsdata indikerar att angreppsättet är robust och kostnadseffektivt även om vissa förbättringar kan genomföras inom givna budgetramar. Små förskjutningar längs berggrundens sprickor har studerats över en period som motsvarar 10 driftår tillsammans med portrycksfördelning, vattenläckage och vattenflödeshastighet. Resultaten visar att berggrunden till största delen är stabil men att små förskjutningar sker och att dessa påverkar distributionen av öppna porer som i sin tur leder till mycket oregelbundna flödesmönster som kan orsaka sprickerosion längs sprickytor och sprickfyllnadsmaterial. I förlängningen kan detta påverka injekteringsskärmens beständighet och därmed berggrundens täthet under dammen.

Numeriska analyser av bergmassans beteende under fyllningsdammar för vattenkraftproduktion.

Bridges are an important element of the infrastructure today. The technical competence has reached high levels in most countries and the limits given to a bridge designer are set by economic restrictions rather than technical skill. The ever lasting chase for more economic solutions and procedures includes both a wish for cheaper constructions as well as for a decrease in the following maintenance costs. The roller bearings used in conventional bridges are known to generate high costs both during construction and due to maintenance, and the possibility to remove these bearings and accompanying expansion joints are therefore investigated since several years. In Sweden, the absence of bridges built with integral abutments has made it difficult to test and evaluate this solution. In 2005, an international project called Intab was launched with the explicit aim to look at different solutions possible to use if joints and bearings are excluded. One of the most common discussed problems concerning bridges built without expansion joints is the accommodation of longitudinal elongation due to temperature variations. A bridge built with integral abutments is often supported by piles made of steel or concrete. The longitudinal elongation of the superstructure induces a displacement and a moment in these piles, which in time may cause a fatigue failure. Therefore it is of big interest to look at the amplitude of these strains. Within the Intab project, a pilot object was built in Nordmaling, ~50 km south of Umeå. It is a 40 meter long and 5 meter wide composite bridge with two steel girders and a concrete deck. The steel piles in this bridge is equipped with strain gauges who are used both for longterm and shortterm measurements. The sampled data from longterm measurement is collected on a computer on site, and then downloaded through a traditional modem. The data from the shortterm measurement is sampled and collected immediately during the test. The shortterm test is performed during both summer and winter conditions, and consists of a lorry passing the bridge while different measurements are done. The result from the measurement is also compared to calculations and a 2-D FE-model. It seems that short-term measurements performed during warmer months, May and October, show better agreement with the FE-simulations than the tests performed during the winter. The used FE-model is based on restrictions from Bro 2004. Regarding the long-term measurements, the obtained strain values are not in a range where fatigue can be considered as a severe problem.