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UPTEC F 16053

Examensarbete 30 hpOktober 2016

Stress and Sliding Stability Analysis of Songlin Rock-filled Concrete Gravity Dam

Max IvedalMax Sundström

Teknisk- naturvetenskaplig fakultet UTH-enheten Besöksadress: Ångströmlaboratoriet Lägerhyddsvägen 1 Hus 4, Plan 0 Postadress: Box 536 751 21 Uppsala Telefon: 018 – 471 30 03 Telefax: 018 – 471 30 00 Hemsida: http://www.teknat.uu.se/student

Abstract

Stress and Sliding Stability Analysis of SonglinRock-Filled Concrete Gravity Dam

Max Ivedal Max Sundström

The construction of Songlin rock-filled concrete gravity dam, located in the Yunnan province, China began in the end of 2015. In this master thesis the finite element method (FEM) based software Abaqus has been used to perform a computational analysis on tension stresses, compression stresses and sliding stability for static conditions. One overflow section and one non-overflow section of the dam have been analysed. The results of the analysis have been evaluated by comparing with Chinese standards for dam safety and is intended to help engineers with making decisions in the construction process of the dam. The measured compressive stress values of both the overflow and non-overflow section are not evaluated to be within safe levels, further evaluation is required to ensure the safety of the dam. The dam is considered to be safe from vertical tension in the analysed region, however an extended evaluation including the whole dam base is recommended. The analysed cross-sections for sliding stability can be considered safe, but further analysis is required to make a conclusion of the sliding stability of the full dam base.

ISSN: 1401-5757, UPTEC F 16053Examinator: Tomas NybergÄmnesgranskare: Per NorrlundHandledare: Jin Feng

Stress and Sliding Stability Analysis ofSonglin Rock-filled Concrete Gravity Dam

Max IvedalMax Sundstrom

Sammanfattning

Konstruktionen av Songlin gravitationsdamm av stenfylld betong, belagen i Yunnanprovinsen i Kina, borjade i slutet av 2015. I det har examensarbetet anvandes detFEM-baserade programmet Abaqus for att utfora en datorbaserad spanningsanalysoch glidstabilitetsanalys av dammen under olika forhallanden i dammens reservoar.Tva av dammens tio sektioner har analyserats, en non-overflow sektion och en over-flow sektion. Dammstrukturen har aven analyserats for stabilitet mot glidning iden har studien. Resultatet av analysen har utvarderas genom att jamfora medkinesiska standarder for dammsakerhet. Tryckspanningsvardena av bade overflowsektionen och non-overflow sektionen uppmattes vara hogre an tillatna varden for attgarantera sakerhet, vidare undersokning ar nodvandig for att garantera dammenssakerhet. Dammen anses vara saker mot vertikal spanning, daremot rekomenderasen fortsatt undersokning dar hela dammens bas inkluderas. De tvarsektioner somanalyserats for glidstabilitet anses sakra mot glidning, det behovs fortsatt analys avsamtliga tvarsektioner for att dra en slutsats for glidstabiliteten for hela dammen.

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Acknowledgments

The project reported in this Master degree thesis has been carried out at the Depart-ment of Hydraulic Engineering in Tsinghua University, Beijing, China from Februaryto June (2016).

We are gratefully indebted to our supervisor Professor Jin Feng for inviting us toTsinghua University, Beijing, and for the advices and interesting discussions. Wewould also like to devote our thanks to PhD student Yiyang Wang, for all the helpoffered to us during our stay.

We would like to thank James Yang from Vattenfall R & D and KTH for makingthe trip possible and for all necessary arrangements and to our subject reader PerNorrlund and our examiner Tomas Nyberg at Uppsala University for all the help.

The project is funded by Energiforsk AB within the frame of dam safety, with Ms.Sara Sandberg as program director, www.energiforsk.se. Aforsk AB have contributedfinancially to make it possible for us to go to China and perform this thesis work.

Uppsala, October 2016

Max Ivedal and Max Sundstrom

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Division of Responsibilities

The responsibilities of the study was divided in the following way: Max Ivedal isthe main author of Sections 1.3-1.5, 2.6-2.9, 3.1, 3.5, 4.4-4.6 and 5.2-5.3. and MaxSundstrom is the main author of Sections 1.1-1.2, 2.1-2.5, 3.2-3.4, 4.1-4.3 and 5.1.In the remaining sections the responsibility was shared.

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Contents

Sammanfattning i

Acknowledgments ii

Division of Responsibilities iii

Symbols, dictionary and abbreviations viiSymbols . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . viiDictionary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . viiAbbreviations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . viii

1 Introduction 11.1 Songlin Rock-filled concrete gravity dam station . . . . . . . . . . . . 11.2 Energy situation in China . . . . . . . . . . . . . . . . . . . . . . . . 4

1.2.1 Hydropower in Yunnan province . . . . . . . . . . . . . . . . . 51.3 Use of rock-filled concrete construction technique in dam building

projects in China . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61.4 Goal of the study . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71.5 Purpose of the study . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

2 General theory 82.1 Concrete gravity dams . . . . . . . . . . . . . . . . . . . . . . . . . . 8

2.1.1 Self-compacting concrete (SCC) . . . . . . . . . . . . . . . . . 82.2 Rock-filled concrete (RFC) . . . . . . . . . . . . . . . . . . . . . . . . 82.3 Compressive strength of RFC . . . . . . . . . . . . . . . . . . . . . . 102.4 Loads on a gravity dam . . . . . . . . . . . . . . . . . . . . . . . . . 10

2.4.1 Design considerations when using RFC technique . . . . . . . 122.5 Stress from hydrostatic pressure . . . . . . . . . . . . . . . . . . . . . 122.6 Uplift pressure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 122.7 Stability and control criteria . . . . . . . . . . . . . . . . . . . . . . . 13

2.7.1 Critical Areas of the dam . . . . . . . . . . . . . . . . . . . . 142.7.2 Compression stress analysis . . . . . . . . . . . . . . . . . . . 142.7.3 Tension stress control . . . . . . . . . . . . . . . . . . . . . . . 152.7.4 Sliding stability . . . . . . . . . . . . . . . . . . . . . . . . . . 15

2.8 Finite element method (FEM) . . . . . . . . . . . . . . . . . . . . . . 162.9 Software details . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

2.9.1 Abaqus software . . . . . . . . . . . . . . . . . . . . . . . . . 162.9.2 UltraEdit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

3 Background data 17

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3.1 Studied dam sections . . . . . . . . . . . . . . . . . . . . . . . . . . . 173.1.1 Overflow section, section 3 . . . . . . . . . . . . . . . . . . . . 193.1.2 Non-overflow section, section 5 . . . . . . . . . . . . . . . . . . 20

3.2 Material parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . 213.3 Estimated water levels . . . . . . . . . . . . . . . . . . . . . . . . . . 213.4 Load cases for stress and sliding stability analysis . . . . . . . . . . . 223.5 Uplift pressure model . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

4 Modeling 234.1 Meshing the model . . . . . . . . . . . . . . . . . . . . . . . . . . . . 264.2 Boundary conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . 274.3 Geostatic model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 294.4 Gravity: Adding the dam to the model . . . . . . . . . . . . . . . . . 304.5 Hydropressure model . . . . . . . . . . . . . . . . . . . . . . . . . . . 304.6 Sliding stability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

5 Results 325.1 Compression stress analysis . . . . . . . . . . . . . . . . . . . . . . . 32

5.1.1 Non-overflow section . . . . . . . . . . . . . . . . . . . . . . . 335.1.2 Overflow section . . . . . . . . . . . . . . . . . . . . . . . . . 35

5.2 Tension stress analysis . . . . . . . . . . . . . . . . . . . . . . . . . . 385.2.1 Vertical tension analysis . . . . . . . . . . . . . . . . . . . . . 42

5.3 Sliding stability analysis . . . . . . . . . . . . . . . . . . . . . . . . . 46

6 Conclusion 47

7 Future recommendations 487.1 Displacement analysis . . . . . . . . . . . . . . . . . . . . . . . . . . 487.2 Dynamic analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 487.3 Extend stress evaluation to dam interior . . . . . . . . . . . . . . . . 487.4 Extend and complete the sliding stability analysis . . . . . . . . . . . 487.5 Extend vertical tension stress evaluation . . . . . . . . . . . . . . . . 487.6 Extend maximum principal stress evalutaion . . . . . . . . . . . . . . 49

8 Discussion 498.1 Difference between section analysis and full dam analysis . . . . . . . 498.2 Mesh independency . . . . . . . . . . . . . . . . . . . . . . . . . . . . 508.3 Element selection for adding uplift pressure . . . . . . . . . . . . . . . 508.4 Element selection for sliding stability analysis . . . . . . . . . . . . . 50

9 References 51

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9.1 Main references . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 519.2 Other references . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52

Appendix xiProject preparations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xi

Background on rock-filled concrete method . . . . . . . . . . . . . . . xiLearning Abaqus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xiTranslation of technical descriptions . . . . . . . . . . . . . . . . . . . xi

Model design procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . xiDesigning in Abaqus . . . . . . . . . . . . . . . . . . . . . . . . . . . xiDesigning in UltraEdit . . . . . . . . . . . . . . . . . . . . . . . . . . xii

Model input-file for check flood load case . . . . . . . . . . . . . . . . . . . xiii

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Symbols, dictionary and abbreviations

Symbols

c = cohesive force [Pa]h = water depth at observed point [m]hb = full water depth [m]H1 = height between the headwater level and the rock foundation [m]H2 = height between the tailwater level and the rock foundation [m]H = the difference between the tailwater level and the headwater level multipliedwith α [m]g = gravitational acceleration [m/s2]K = safety factor for sliding stability evaluation [−]Kc = safety factor evaluating compression stress [−]L = length of the dam [m]X = distance from dam heel to the drainage gallery [m]α = strength reduction coefficient [−]γ = the gravity factor acting in direction opposite of gravity on the elements affectedby uplift pressure. [m/s2]ρc = concrete density [kg/m3]ρw = water density [kg/m3]σ = normal stress [Pa]σv = vertical force from hydropressure [Pa]]σo = orthogonal force from hydropressure onto dam surface [Pa]]τ = shear stress [Pa]]τF = shear strength [Pa]]d = maximum node distance in mesh element [m]φ = angle of internal friction [°]C = measured compression stress [°]Cc = compression strength of the concrete [°]a = maximum area allowed to be exterted to vertical tension stress [°]

Dictionary

C15: A concrete mix which 28 days after placement can withstand a compressionof 15 MPa (15 N/mm2 ).C20: A concrete mix which 28 days after placement can withstand a compressionof 20 MPa (20 N/mm2).

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Compressive stress: Stress on a material leading to compression and shortens thematerial.Dam heel: The part of the upstream side of the dam near the rock foundationDam toe: The part of the downstream side of the dam near the rock foundationNon-overflow: The section of a dam constructed to withstand flood flows.Overflow: A section of a dam designed to discharge flood flows.Poisson ratio: The ratio of transverse contraction strain to longitudinal extensionaxial stress resulting from uniformly distributed axial stress below the proportionallimit of the material.Spillway: The structure on the overflow section which the flood water will flow on.Young’s modulus: The ratio of stress along an axis to the strain along that axis,i.e the measure of stiffness in an elastic material.

Abbreviations

CC = conventional concreteFEM = finite element methodRFC = rock filled concreteSCC = self compacting concrete

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1 Introduction

In this master thesis a computational analysis on tension stresses, compressionstresses and sliding stability of the Songlin rock-filled concrete dam has been per-formed during static conditions. Simulations are done using the finite elementmethod-based software Abaqus. The dam structure will be analysed at differentpool water level conditions. The analysis is made for two different sections of thedam, one overflow section and one non-overflow section.

1.1 Songlin Rock-filled concrete gravity dam station

Songlin rock-filled concrete gravity dam is situated along Jinsha river near Zhaotongin the province of Yunnan in southwestern China , see Figures 1.1 and 1.2. Locatedat a maximum elevation of 1961.2 m above sea level, it stands at 90.0 m height anda has width of 230.0 m. The construction of the dam began in the end of 2015,when finished it will be one of the largest Rock-filled concrete (RFC) dams built inChina, see Figures 1.3-1.5.

Figure 1.1: Map of the provinces in China. The arrow indicates the location ofYunnan province. (www.d-maps.com)

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Figure 1.2: Map of the Yunnan province. The arrow indicates the location of Zhao-tong region. (www.d-maps.com)

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Figure 1.3: Drawing of Songlin dam and surroundings. (Image from Jin, F.)

Figure 1.4: Songlin dam construction site. (Image from Jin, F. Date: 24/5-2016)

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Figure 1.5: Songlin dam construction site. (Image from Jin, F. Date: 24/5-2016)

1.2 Energy situation in China

The Peoples Republic of China has in recent years gone through a massive, unpar-alleled economical development. This extensive economic and social progress hasresulted in a rapid increase in energy consumption, see Figure 1.6. A key issue is tosupply and generate enough energy to meet the increasing demand. (Hennig et al.2013)

Extensive effort is made to to modernize the grid and provide effective energy conver-sion and transport. The majority of energy demand comes from the large industrialand urbanized areas in the eastern and southern parts of the country. Electricity ismainly produced in the less populated northern and western parts of the country.(Hennig et al. 2013)

About two thirds of the installed capacity is from thermal power (coal, gas, petroleum)which remains the primary sources of producing electricity, but increased effort hasbeen made to utiliize more sustainable resources, see Table 1. (Liu. 2013)

China’s hydropower capacity is rapidly increasing and the aim is to have installed350 GW by 2020. Due to the large investments in hydropower China is the most

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active nation in the field of hydropower development. (Liu. 2013)

Figure 1.6: Energy consumption in China over time. SCE stands for standard coalequivalent. (Based on statistics from www.stats.gov.cn)

Table 1: The distribution of energy sources in China. Use of non-fossil resourceshas increased relative to fossil resources since 1990. (Based on statistic fromwww.stats.gov.cn)

Year Coal [%] Crude Oil [%] Natural Gas [%] Hydro-power, Nuclear Power, Wind Power[%]1990 76.2 16.6 2.1 5.12000 69.2 22.2 2.2 6.42005 70.8 19.8 2.6 6.82010 68.0 19.0 4.4 8.62013 66.0 18.4 5.8 9.8

1.2.1 Hydropower in Yunnan province

The Yunnan province holds one of the highest hydropower potentials of all theprovinces in China, exceeding 90 GW. Geographical conditions in the area are highlysuitable for hydropower installations. Major rivers such as Jinsha-, Mekong-, andNanpan rivers change their topography through a long transition here, flowing fromhigh altitudes to lowland areas. Recent developments in large projects along these

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major rivers has made the region a key provider of electric energy for the country.(Hennig, et al. 2013)

1.3 Use of rock-filled concrete construction technique indam building projects in China

RFC-technique has until now been applied successfully in more than 60 hydraulicengineering projects in China. (An, et al. 2014)

The first use of the RFC-technique in engineering projects was in 2005. Since thenit has been used successfully in more than 80 projects. The majority of the projectshas been small-and medium sized projects. Projects with the dam height of 30-50m stands for about 40.3 % and dams with the height of 50-70 m consists of about48.6 %. 84.4 % of the projects are regarding RFC gravity dams, where 71.8 % ofthe projects are to construct them and 12.6 % is to reinforce them. The remaining15.6 % are RFC arch dam projects, where 14 % of the projects are to reinforce themand 1.6 % is to build them. Figure 1.7 displays the amount of RFC used each yearand in Figure 1.8 the initiated RFC projects per year can be seen. (ICOLD, 2015)

Figure 1.7: Used RFC volume per year in China. (ICOLD, 2015)

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Figure 1.8: Initiated RFC construction projects per year in China. (ICOLD, 2015)

Apart from constructing new gravity dams and arch dams, RFC technique hasproved useful in repair and rehabilitation projects where old materials can be utilizedto replace necessary rock blocks in the RFC composition. (ICOLD, 2015)

1.4 Goal of the study

The goal of this thesis is to perform a computational stress and stability analysison the Songlin rock-filled concrete gravity dam, situated in the Yunnan Provincein China. The analysis will be performed using the FEM-based software Abaqus.The observed tension stresses, compression stresses and the sliding stability is to beevaluated using Chinese standards.

1.5 Purpose of the study

The purpose of the study is to study the properties of RFC, quality control in con-struction process and verification of design. Analysis will help construction engineersin making project decisions. Results will be studied comparing with the monitoringdata after the reservoir impound.

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2 General theory

This section will give the reader a brief introduction to concrete gravity dams, self-compacting concrete (SCC) and rock-filled concrete (RFC). The loads and stressesacting on a gravity dam are introduced, as well as the Chinese standards for analysingdam safety. Furthermore the finite element method (FEM) and the used computersoftware are explained.

2.1 Concrete gravity dams

A gravity dam use its own weight to withstand hydropressures from the reservoir.They are usually constructed on a straight axis, but it is possible to adapt theconstruction procedure to adapt to the conditions at the building site. A concretegravity dam consist of two types of sections: non-overflow sections and overflowsections. Conventional mass placed concrete and roller-compacted concrete are themethods that traditionally have been used to construct the concrete gravity dams.There are however methods like the rock-filled concrete technique which has beenused more frequently in dam construction in recent times. (USACE, 1995)

2.1.1 Self-compacting concrete (SCC)

The rock-filled concrete technique is based on the characteristics of self-compactingconcrete (SCC), a material that was invented in Japan in the 1980s. Compared tonormal concrete, SCC has higher fluidity and is more resistant to aggregate segrega-tion during placement. Thus, it can flow through and fill voids in an irregular formusing only its own weight. (An, et al. 2014)

SCC reduces the need for vibration compaction which in turn make it less laborexpensive. However, SCC has a higher cement content than conventional massconcrete, increasing the hydration temperature which is one reason for the limiteduse of SCC in hydraulic structures. (Okamura, et al. 2003)

2.2 Rock-filled concrete (RFC)

A concrete construction method named rock-filled concrete (RFC) based on mixingself-compacting concrete (SCC) with rocks was presented in 2003 by Jin, F. and An,H. from Tsinghua University in China. One RFC unit is produced by pouring SCConto a form filled with blocks of rock larger than 30 cm in diameter. SCC, having

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good fluidity and being segregation resistant is able to fill the voids between therocks. See Figure 2.1.

Using the RFC-construction procedure, a large portion (50-55 % of the form volume)will be covered with rocks meaning less concrete will be required to fill the volumeof the formwork compared with other concrete construction methods. (An, et al.2014).

A study show that using of RFC instead of conventional concrete lowers the totalenergy consumption with 55 % and reduces the CO2-emissions with approximately64 %. (Jin, F & An, H. 2008.).

Figure 2.1: Illustration of RFC and its components. (Jin, F.)

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Table 2: Advantages and disadvantages using RFC-method comparing to conven-tional concrete construction methods. (Lundell, 2009).

Advantages of RFCLess concrete requiredLess drying shrinkageLower hydration temperatureReduced laborNo need for surface treatmentLower total costsIncreased construction speedLower environmental impactDisadvantages of RFCReinforcing is more difficultFormwork quality important due to high fluidity of SCCStaff training is requiredVariations in the strength of the material composition

2.3 Compressive strength of RFC

In previous experiments to research the characteristics of RFC the compressivestrength has been tested. These tests compared the compressive strength of RFCwith the compressive strength of SCC. Nine RFC samples were used, the resultsrevealed a wide spectrum of compressive strengths among its specimens, some spec-imens proved stronger than SCC while some proved weaker than the SCC. Theaverage compressive strength of the RFC specimens was however 1.27 times that ofthe SCC. (An, et al. 2014)

The wide spectrum in compressive strength among the specimens is important totake into consideration in construction. For example in the construction of a damstructure these results indicate that there can be significant variations in the materialstrength in different regions of the dam. This less predictable variation feature ofRFC can be considered a disadvantage for a construction phase.

2.4 Loads on a gravity dam

A gravity dam structure is affected by several different loads which are explained inthis section. Figure 2.2 illustrates the loads acting on a concrete gravity dam.

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• Earth-and silt pressure: Eroded materials will settle on the bottom of theupstream part of the dam and cause a pressure. (Jansen, 1988)

• Earthquake: A dynamic load which can have a large impact on a dam struc-ture and is vital to predict for dam modeling. (Jansen, 1988)

• Ice: The dam is thin at the water surface and therefore a thick ice with a largeload can have a significant impact on the dam. (Jansen, 1988)

• Hydro-static pressure from reservoir: The water pressure on the up-stream face of the dam from the reservoir. (USACE. 1995)

• Hydro-static pressure from tailwater: The downstream water pressureon the dam. (USACE. 1995)

• Self weight: The gravitational force from the self weight of the dam have asignificant impact on the model. (USACE. 1995)

• Temperature: Variations in temperature conditions will result in hardeningof the concrete causing strains which can lead to cracks in the concrete. Thisis a difficult problem that will be a concern during both the construction andthe whole lifespan of the dam. The problem is dependent on which climatethe dam is located in. (USACE. 1995)

• Uplift pressure: The pressure from headwater and tailwater results in avertical load acting in a direction opposite to the direction of gravity. Thispressure will lift the dam. (USACE. 1995)

Figure 2.2: Loads acting on a concrete gravity dam. Seismic load and wave pressureare dynamic loads.

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2.4.1 Design considerations when using RFC technique

Design of a RFC gravity dam should follow similar guidelines as designing traditionalmass concrete dams in terms of stability and acceptable stress levels. RFC gravitydams should be designed to the same criteria as traditional concrete gravity damswith respect to stability and allowable stresses of the dam body and foundation.(ICOLD, 2015)

2.5 Stress from hydrostatic pressure

The pool reservoir will exert a orthogonal force on the dam surface on both upstream-and downstream side of the dam according to:

σo = ρwgh (1)

where h is the water depth at the observed point, ρw is the density of water, g isthe gravitational acceleration.

Similarly, the pool reservoir will exert a vertical pressure on the rock foundation onboth upstream-and downstream side of the dam according to:

σv = ρwgh (2)

where hb is the maximum water depth in this case.

2.6 Uplift pressure

Water seepage effects within the dam will create an uplift pressure acting in anopposite direction of gravity. The uplift pressure is dependent on the relationshipbetween the densities of the used concrete and the water described in Equation 3.

γ =ρwρc

∗ g (3)

where ρc is the density of the concrete in the dam, ρw is the water density and g isthe gravitational acceleration.

The uplift pressure will also be dependent on the upstream and downstream waterdepth and the positioning and efficiency of the drainage gallery.

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Figure 2.3: Uplift pressure distribution with a drainage gallery.

L is the length of the dam and X is the distance from the upstream side to thedrainage gallery. The height H is calculated using:

H = α(H1 −H2), (4)

where H1 is upstream water level, H2 is downstream water level, α is the strengthreduction coefficient of uplift pressure where there are anti-seepage curtain and drainholes. (Jin, F)

2.7 Stability and control criteria

Three criteria are to be analysed according to Chinese standard safety analysis code:

• Compressive stress control

• Tension stress control and vertical tension control in the dam base

• Sliding stability control

(Ministry of Water Resources & Electric Power of P.R.C, 1979, 1984)

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2.7.1 Critical Areas of the dam

Areas of the dam where stresses may cause extra difficulties need to be handled withextra care. In general, areas in where different materials connect (around dam base),areas which may be subject to high torque and possible weak planes within the damrequires careful analysis and evaluation. These areas are displayed in Figure 2.4.

The region around the dam heel (green area in Figure 2.4) is expected to be affectedby tension stress due to the orthogonal force from the water in the reservoir on theupstream side of the dam. These orthogonal stresses cause a torque effect whichmay cause tension stresses at the dam heel.

The dam toe region (red area in Figure 2.4) is expected to be affected by compres-sion stress due to the weight from the water on the upstream side which create anorthogonal force which in turn is expected to accumulate compression stresses ontothe dam toe region.

Figure 2.4: Illustration of a dam model with critical areas for compression stress(red), sliding (blue) and tension stress (green).

2.7.2 Compression stress analysis

The measured negative minimal principal stress in the simulations will represent thecompressive stresses in the dam structure at specified water conditions. For everyload case of water conditions the measured compressive stress for each respective

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simulation is to be compared with compressive strength of the material. For thecompressive stress to be considered on a safe level it needs to fulfill:

C < KcCc (5)

where C is the measured compression strength in the dam, Kc is the compressionsafety factor and Cc is the allowed cubic compression stress for the concrete.

2.7.3 Tension stress control

In analysing the maximum principal stress the positive values will represent tensionstresses within the dam. Areas exerted to tension stresses should be identified forfurther evaluation. The main purpose of the maximum principal stress analysis isto identify possible weak areas and where they may occur in the dam structure.

Another part of the tension stress analysis is to investigate if areas near the damheel is exerted to vertical tension stress. Vertical tension stress in this area give arisk of creating cracks in the concrete. Chinese standards state that the length ofthe area at the dam heel possibly exerted to vertical tension need to be less than 8percent of the length of the entire dam base. See Figure 2.5.

Figure 2.5: Illustration of a gravity dam, where L is the length and a is the allowedarea exerted to vertical tension.

2.7.4 Sliding stability

Sliding of a dam structure need to be analysed along the base of the dam and atweak planes within the dam.

The sliding stability is measured as a factor of safety K which is defined as the ratiobetween the shear strength τF and the applied shear stress τ in Equation 6 wherethe shear strength is defined according to the Mohr-Coulomb Failure Criterion.

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K =τFτ

=σ ∗ tan(φ) + c

τ(6)

where σ is the normal stress caused by horizontal and vertical stresses, c is the co-hesive force and φ is the angle of internal friction of the material. (USACE, 1995)

In Chinese standards, the factor of safety K has to exceed 3.0 during static conditionsin order to be considered safe against sliding. (Jin, F)

2.8 Finite element method (FEM)

The finite element method is used extensively by engineers and scientists to makemathematical models and numerically solve complex problems. Analyses are carriedout largely to obtain insight into and ideally predict natural phenomena. Utilizingthis information can make designs more cost effective and extensively predict struc-tural issues that may occur.

FEM divides the calculated area into element cells with corresponding base func-tions. The choice of the element cells can be based on the geometry of the modelthat is to be studied. Analysis will be more accurate and extensive the more elementcells that are used. Simulation accuracy will highly depend on the computationalresources. (Jansen, 1988)

2.9 Software details

2.9.1 Abaqus software

Abaqus is a suite of powerful engineering simulation programs. Being based onthe finite element method, it can perform simple linear analyses as well as morechallenging nonlinear simulation problems. In this project, structural stresses aresimulated and analysed. (ABAQUS 6.9 User Documentation)

2.9.2 UltraEdit

UltraEdit is a program for text file editing. Our design model from ABAQUS wasoutput as an input file which could be edited in UltraEdit. Design of the simulationwas done in UltraEdit.

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3 Background data

This section will introduce material parameters, dimensional data and drawings forthe Songlin dam. The data on water conditions which are used in the simulation isintroduced.

3.1 Studied dam sections

The Songlin rock-filled concrete gravity dam consist of ten sections; nine non-overflow sections and one overflow section. See Figure 3.1. For the modeling of thedam, one non-overflow section and one overflow section was studied. The Abaqus-model of the Songlin dam was designed based on drawings and dimensional dataprovided by Professor Jin Feng. The dam dimensions can be seen in Table 3.

Table 3: Dam dimensions.

(a) Section 3: Overflow section

Width [m] Length [m] Height [m]23.40 78.57 90.00

(b) Section 5: Non-overflow section

Width [m] Length [m] Height [m]23.00 78.57 90.00

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Figure 3.1: The Songlin rock-fill concrete gravity dam seen from upstream end.Section 3 (overflow section) and section 5 (non-overflow section) have been studied.

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3.1.1 Overflow section, section 3

The overflow section has a spillway designed to lead overflowing water during floodconditions. The section consist of RFC together with a cover of SCC at upstreamsurface, downstream surface and between the rock foundation and the RFC. SeeFigure 3.2.

Figure 3.2: Section 3: Technical description of overflow section.

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3.1.2 Non-overflow section, section 5

The non-overflow section consist of RFC and a layer of SCC underneath the dambetween the RFC and the rock foundation. Another layer of SCC is at the upstreamsurface. The section has a drainage gallery with the lowest position at 2.5 m abovethe rock foundation. See Figure 3.3.

Figure 3.3: Section 5: Technical description of non-overflow section.

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3.2 Material parameters

The dam consist of two kinds of construction material: RFC (rocks covered withC15-concrete) and SCC (C20-concrete). C15-concrete has a compression strengthof 15 MPa while the C20-concrete has a compression strength of 20 MPa. Materialdensity, Young’s modulus and Poisson ratio for the two types of concrete and forthe rock foundation have been used for the modeling, the data is displayed in Table4.

Table 4: Material properties.

Material Density [kg/m3] Young’s modulus[GPa] Poisson RatioRock 2700 5.5 0.19SCC (C20) 2450 25.5 0.167RFC (C15) 2490 38.5 0.167

Other relevant parameters:

• Safety factor for evaluating compression of concrete in Chinese standards isKc=0.25. (Wang, Y)

• Strength reduction coefficient of uplift pressure α=0.25 where there are anti-seepage curtain and drain holes. (Jin, F)

The shearing parameters of the rock foundation are:

• A cohesive force c with unit cohesive strength of 0.98 MPa.

• Coefficient of internal friction tan(φ)=1.10.

(Jin, F)

3.3 Estimated water levels

The water levels in the upstream and downstream parts of the dam will depend onthe conditions in the reservoir. In this study, water levels for an estimated designflood case and an estimated check flood case was used in the simulation.

Design flood is the estimated water level in the upstream side of the dam during aflood estimated to occur every five years.

Check flood is the estimated level in the upstream side of the dam during a floodestimated to occur every 50 years.

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Tailwater is the estimated water level in the downstream section. Two values fortailwater are given, corresponding to check flood and design flood level respectively.

The estimated water levels are displayed in Table 5.

Table 5: Estimated water levels

Water level Height (above sea level) [m]Check flood 1960.43Design flood 1959.56Tailwater level at design flood 1880.88Tailwater level at check flood 1881.80

3.4 Load cases for stress and sliding stability analysis

The basic loading conditions used for the RFC gravity dam stability analysis arethe same as when studying conventional concrete gravity dams.

From the loads explained in Section 2.4 the following loads have not been taken intoconsideration for the static analysis in this study.

• Ice is rare since weather conditions in Yunnan province can be consideredtropical, therefore no ice load will occur.

• Earthquake simulation is not covered in this study.

• Silt pressure can be considered small relative the other loads and is neglectedin the model.

• Temperature will not have enough impact to be considered relevant to thisstudy, since the temperature variations in the area are not significant.

The following water level conditions are to be simulated in this study:

Estimated design flood condition:

• Pressure from headwater at estimated design flood

• Pressure from tailwater at estimated design flood

• Uplift pressure

Estimated check flood condition:

• Pressure from headwater at estimated check flood

• Pressure from tailwater at estimated check flood

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• Uplift pressure

3.5 Uplift pressure model

In order to model the uplift pressure the gravitational force is reduced on elements inthe dam. The force reduction will simulate the internal water pressure from seepageswithin the dam. In Chinese procedure, an area is created with an approximate shapeof the volume region that is exerted to uplift, see Figure 2.3. Rotating the shape 180degrees around the horizontal axis and project the shape onto the dam will markwhich volume region whose gravitational acceleration should be reduced to modelthe approximated uplift pressure, see Section 4.5.

Using Equation 3 to calculate the uplift pressure γ give:

γ =ρwρc

∗ g =1000 kg/m3

2490 kg/m3∗ 9.82 m/s2 = 3.94 m/s2, (7)

where the dam in this model is approximated to only consist of RFC with densityρc, ρw is the water density and g is the gravitational acceleration.

Using the water depth data from Section 6 and the strength reduction coefficientα=0.25 (introduced in Section 3.2). The region of the dam which is to be affectedby the uplift pressure in the modeling step (Section 4.5) can be identified by usingEquation 4.

4 Modeling

The modeling section aims to give the reader an overview of how a dam modelwas created based on the research data and general dam theory. It also explainsapproximations used. For a more extensive view of each modeling step in Abaqusand in UltraEdit, see Appendix 9.2. This section covers the meshing procedure aswell as the boundary conditions that was set for the simulations.

The non-overflow and the overflow section was simulated separately, Abaqus modelsof the dam sections are displayed in Figures 4.1, 4.2 and 4.3. The modeling procedurewas divided into three steps for each section. This was essential in order to predictinitial stresses in the rock foundation and include this data in the full analysis. Whenintroducing the dam in the model there are stresses within the dam and stresses fromthe dam weight that have an effect on the rock foundation. By dividing the modelinginto three steps the study get an extensive view on initial conditions in the region

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where the dam construction is set. The study also covers the occurring stressesbefore and after water conditions are introduced to get a view of stress effects ateach step. The modeling is divided into the following three steps:

• Geo-static step: Predict the initial stress in the ground beneath the dam struc-ture.

• Gravity step: Adding the dam to the model. Predict stresses within the damand stresses from the dam on the rock foundation due to the weight of thedam.

• Water step: Hydrostatic pressure, uplift pressure and vertical water pressureare introduced in the model.

In Figures 4.1-4.4 the red regions are rock, the white regions are SCC (C20) and thegreen regions are RFC (C15).

Figure 4.1: Model of non-overflow section seen from upstream side.

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Figure 4.2: Model of non-overflow section seen from downstream side.

Figure 4.3: Model of overflow section seen from downstream side.

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Figure 4.4: Closeup on the tetrahedron-meshed part of the dam built against themountain.

4.1 Meshing the model

The so called ”Global seeds function” together with the built-in tetrahedron-shapedmesh control was used for the creation of the mesh in Abaqus. Each tetrahedronelement had a maximum distance of d=2.5 m between its nodes (see Figure 4.5).Using the Global seeds function it is possible to mark a region and Abaqus meshesit at best ability independently of the material composition. The dam structure wasmeshed separately from the ground foundation below, both was given its individualmesh. For a closeup view of the mesh, see Figure 4.4.

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Figure 4.5: Tetra-shaped element used for the meshing procedure where d is thedistance between nodes.

4.2 Boundary conditions

Two of the ten dam sections of the dam are simulated in this model. Modeling thesurrounding dam sections and rock is handled by setting boundary conditions forthe surroundings of the modeled section. These conditions limit the movement ofthe modeled dam section and the rock foundation. The boundary conditions usedin this simulation are presented in Figure 9.1 in Appendix.

In Figures 4.6-4.7 the red-colored regions are given boundary conditions restrictingthem from moving in the direction normal to the surface while being free to movein directions orthogonal to the normal direction. The surfaces colored in green(upstream surface of dam, downstream surface of dam and the top of the rockfoundation) are given the boundary condition of moving freely.

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Figure 4.6: View of the used boundary conditions on the dam model seen fromupstream side.

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Figure 4.7: View of the set boundary conditions on the dam model seen fromdownstream side.

4.3 Geostatic model

The ground tension is modeled before the dam is present. The dead load of theground and its gravitational impact is analysed. The ground is modeled to be 1.5times the dam height in z-direction. In y-direction the ground is modeled to be fourtimes the length of the dam. In x-direction the ground model is of equal width asthe dam. See Figure 4.8.

The initial ground tension is necessary for an accurate model, basically how theground is affected by gravity. The ground was analysed without influence from damand the water conditions. The data from the initial tension was added to the fullsimulation. Results can be useful in further studies to analyse how stresses from thedam and the water affect the ground comparing with how the ground affect itself.

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Figure 4.8: Model of the ground tension before dam building impact

4.4 Gravity: Adding the dam to the model

The dam model is built based on the technical descriptions in Figures 3.2 and 3.3respectively. The simulated sections are both built against the mountain side. Theconcrete structure has been designed to fit the geometry of the mountain, see Figure4.4. Results from this step can be used to evaluate the stresses in the model beforewater conditions are introduced and thereby identifying how the stress distributionchange with every introduced step and with external conditions.

4.5 Hydropressure model

Introducing water in the pool reservoir is modeled as follows:

• Elements affected by uplift pressure are selected, see Figure 4.9 to count foruplift pressure, according to the model in Section 3.5. Selected elements aregiven a reduced gravitational force to account for the uplift pressure at thespecific simulated load case. (Boberg, B & Holm, D. 2012)

• Hydrostatic pressure on upstream and downstream surfaces is modeled accord-ing to Equation 1 for the two load cases explained in Section 3.4.

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• The vertical pool pressure from the reservoir will act on the rock foundationon upstream and downstream sides and is modeled according to Equation 2.

Figure 4.9: Elements (in red) that are affected by uplift pressure.

4.6 Sliding stability

Shear stress and vertical stress on the dam base surface is required to assess thesliding stability using Mohr-Coulomb Failure Criterion (introduced in Section 2.7.4).Stresses were analysed for a number of elements at four separate cross-sections ofthe dam base, see Figure 4.10. The measured stress at each element were used tocalculate the safety factor K for each cross-section for each load case explained inSection 3.4.

According to Chinese standards, the safety factor K should be higher than 3.0 forthe analysed cross-section to be considered safe against sliding. The lowest averagevalue calculated from all the cross-sections will be the K-value for the whole damstructure for that specific load case. In that way the most dangerous scenario isassessed and compared with the acceptable K-value.

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Figure 4.10: The tetrahedron elements (in red) selected for vertical and shear stressanalysis.

5 Results

In this section the simulation results for the different load cases are presented for therespective dam sections. Resulting stress levels are to be compared to acceptablestress levels set by Chinese standards. Positive stress values in the figures indicatetension stress. Negative stress values indicate compression stress.

5.1 Compression stress analysis

Compression stress is analysed by evaluating the minimal principal stresses fromthe Abaqus-simulation. The compression stress for each load case must be less thanthe compressive strength of the concrete multiplied with the safety factor Kc=0.25(from Section 3.2) to be considered safe according to Chinese standards, see Section2.7.2. The compressive strength of the concrete types in the dam structure (C15

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and C20) have been used to calculate the allowable minimum principal stresses, seeTable 6.

Table 6: Minimal principal stress in Chinese standards. Negative stress values inthe results analysis indicate compression stress.

Concrete type C15 C20Compressive strength [MPa] -15.00 -20.00Allowable Minimal principal stress [MPa] -3.75 -5.00

5.1.1 Non-overflow section

Figure 5.1: Minimum principal stress [Pa] for non-overflow section at design floodconditions.

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Figure 5.2: Minimum principal stress [Pa] for non-overflow section at check floodconditions

The measured stress levels in Figures 5.1 and 5.2 can not be considered on a safe levelaccording to Chinese standards (see Table 6). Stresses in both simulations exceedthe maximum allowable compression stress near the dam toe. A tendency is thatthe compressive stresses increase closer to the dam foundation and is accumulatednear the dam toe.

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5.1.2 Overflow section

Figure 5.3: Upstream side: Minimum principal stress [Pa] for overflow section atdesign flood conditions

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Figure 5.4: Downstream side: Minimum principal stress [Pa] for overflow section atdesign flood conditions

The measured stress levels in Figures 5.3 and 5.4 can not be evaluated as safe andacceptable according to Chinese standards (see Table 6) since the interior of the damis not evaluated. The regions with with high compression stresses near unacceptablelevels on the dam surface is located near the dam toe and in the rock foundation.

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Figure 5.5: Minimum principal stress [Pa] for overflow section at check flood con-ditions.

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Figure 5.6: Minimum principal stress [Pa] for overflow section at check flood con-ditions.

The measured stress levels in Figures 5.5 and 5.6 can not be evaluated as safe andacceptable according to Chinese standards (see Table 6) since the interior of the damis not evaluated. The regions with with high compression stresses near unacceptablelevels on the dam surface is located near the dam toe and in the rock foundation.

5.2 Tension stress analysis

Tension stress is analysed by evaluating the maximum principal stresses from theAbaqus-simulation. The main purpose of the tension control safety analysis is topredict possible weak areas in the dam structure. By identifying regions with largetension stresses and make further analysis on these regions will make a more completesafety analysis. (Jin, F)

Recommendation on how to further extend the tension control analysis is done inSection 7.6

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Figure 5.7: Maximum principal stress [Pa] for non-overflow section at check floodconditions. Areas with tension stress in blue and red.

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Figure 5.8: Maximum principal stress [Pa] for non-overflow section at design floodconditions. Areas with tension stress in blue and red.

Non-overflow section: Tension stress is mainly observed in the upper areas of theoutside layer of the dam and in the dam base. Tension stress can be observed onthe rock foundation on upstream and downstream sides of the dam.

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Figure 5.9: Maximum principal stress [Pa] for overflow section at check flood con-ditions. Areas with no tension stress is in black.

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Figure 5.10: Maximum principal stress [Pa] for overflow section at design floodconditions. Areas with no tension stress is in black.

Overflow section: Tension stress is mainly observed in the upper areas of the outsidelayer of the dam and in the dam base. Tension stress can be observed on the rockfoundation on upstream and downstream sides of the dam. Higher stresses doesoccur near the dam heel which need to be analysed further.

5.2.1 Vertical tension analysis

Tension stress is analysed by evaluating the maximum principal vertical stressesfrom the Abaqus-simulation. Theory on vertical tension control analysis was givenin Section 2.7.3. The main purpose of this analysis is to investigate if there is verticaltension in the dam base region near the dam heel. Figures 5.11-5.14 illustrates thevertical tension stress distribution on the dam models. Note that only the outsidelayer of the dam is analysed.

Recommendations on how to further extend the evaluation in this section is madein Section 7.5.

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Figure 5.11: Vertical tension [Pa] distribution for non-overflow section at designflood loading conditions.

Vertical tension stress can not be found in the outside layer of elements aroundthe dam heel. Vertical tension (in green color) is observed mainly on the upstreamsurface of the dam.

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Figure 5.12: Vertical tension [Pa] distribution for overflow section at design floodloading conditions.

Vertical tension stress (in green color) can not be found in the outside layer ofelements around the dam heel. Vertical tension is observed mainly on the upstreamsurface of the dam.

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Figure 5.13: Vertical tension [Pa] distribution for non-overflow section at checkflood loading conditions.


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Figure 5.14: Vertical tension [Pa] distribution (in green color) for overflow sectionat check flood loading conditions.


5.3 Sliding stability analysis

The safety factor K for each cross-section was calculated using Equation 6. Amean value from the four cross-sections was calculated to retrieve a single K-valuethat indicates the sliding stability in the dam base surface at specified pool waterconditions. According to Chinese standards the minimum value of K should not belower than 3.0 in order to consider the cross-section of the dam structure to be safeagainst sliding, see Section 2.7.4.

After analysing Table 7 and comparing the values of the calculated K to the Chinese

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standard value, it can be seen that all of the calculated K values are larger than 3.0for the four analysed cross-sections. An extended analysis would include analysis ofall cross-sections, such extended analysis would be neccessary for making conclusionof the dam safety in terms of sliding stability.

Table 7: K-values of safety against sliding

(a)

Check flood Non-overflow OverflowSafety factor K 4.40 4.10

(b)

Design flood Non-overflow OverflowSafety factor K 3.42 3.88

6 Conclusion

In the outside layer of the overflow section there are stresses higher than the allowedcompression stress values in Table 6. The section can not be considered safe basedsolely on this results evaluation, further evaluation is required.

The non-overflow section can not be considered safe against breakage. Stresses in theoutside layer of the dam concrete structure do exceed the allowed compression stressvalues in both simulations of flood cases. These results are discussed in Section 8.

No vertical tension stress can be observed in the outside layer at the dam heel forboth sections at both load cases. The tensile stress area is less than 8% which wasthe condition for safety. An extended evaluation would be useful in this case thatwould include the whole dam base, this is discussed in Section 7.6.

For the sliding stability analysis (see Section 4.6), the safety factor K was above 3.0for all simulated cases, which is the critical condition in Chinese standards. It shallbe noted that since only four cross-sections were analysed for sliding stability theconclusion on whether the dam is stable against sliding cannot be done based onlyon the results of this study. Further evaluation which would include the analysingall elements in the dam base is required to make a conclusion of the sliding stabilityof the dam.

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7 Future recommendations

7.1 Displacement analysis

Displacement analysis is another form of criteria mentioned in the Chinese standardswhich can be conducted in order to find possible weak areas in the dam structure.

7.2 Dynamic analysis

A further study of the Songlin RFC concrete gravity dam is to make analysis duringdynamic conditions. Dynamic simulation in Abaqus would analyse the durabilityof the dam during earthquake conditions. Wave loads and seismic loads would beadded to the dam model, see Figure 2.2.

7.3 Extend stress evaluation to dam interior

In all analysis made in this study, stress distribution were analysed on the surfaceof the modeled 3D-dam structure. It is of importance to analyse the stress all theelements within the dam interior in order to complete the analysis. The simulationpin-points extreme values, if extreme values would occur inside the dam it would becovered by this analysis.

7.4 Extend and complete the sliding stability analysis

In this study, the sliding stability analysis was done on cross-sections of the dambase, see Section 4.6. To retrieve a complete evaluation of the sliding stability ofthis dam it is necessary to evaluate the safety factor of all cross-sections in the dambase.

7.5 Extend vertical tension stress evaluation

In Section 5.2.1 the objective is to analyse if there exists vertical tension stresses atthe dam base near the dam heel, if vertical tension can be identified it is necessaryto evaluate to what extent the dam base is affected. A further recommendation isto extend the study by evaluating the full dam base, not only the outside layer ofthe dam near the dam heel which is covered in this study.

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In this study the analysis was made only to find the region in which vertical tensionstresses was identified. An extension of the evaluation would be to discretize thestress evaluation further.

7.6 Extend maximum principal stress evalutaion

In Section 5.2 the Maximum Principal Stress Analysis is evaluated to identify ifthere are areas within the dam that are subject to tension stresses. In this study theanalysis was performed to identify where tension stresses were occurring (markedin blue) in the the dam structure as well as identifying the maximum tension stressvalue for the simulation. Similarly to the recommendation in Subsection 7.5, oneapproach to further evaluate would be to discretize the results. Extending the eval-uation would provide provide an extensive view on how large the tension stressesare in the dam, not only indicating where tension stress is occurring and how largethe maximum tension stress value is.

8 Discussion

8.1 Difference between section analysis and full dam analy-sis

Simulating a single dam section may give different results from modeling the fulldam including all sections. Using the boundary conditions in 4.2, the dam and therock foundation is totally fixed in the x-direction, see Figure 4.6. These conditionsmean that all stress will affect the simulated section without any support from thesurrounding dam sections and the rock foundation. In a full dam analysis thereis reason to believe that the stress would be distributed to the surroundings to ahigher extent. Based on this, it is possible that a one-sectional analysis like the oneperformed in this study is conservative and that stresses in the analysed dam sectionwould be lower if the simulated model would include all sections. For similar reasons,the sliding stability analysis is possibly on the conservative side as well since it isdependent on vertical stresses and shear stresses within the dam structure. Thereis reason to believe that K-values would be higher in a sliding stability analysis of amodel including all dam sections.

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8.2 Mesh independency

An aspect to the simulation is mesh-dependency of the results in the stress andsliding stability analysis. Ideally, the mesh would be as small as possible to pin-point weak areas with high accuracy. A bottleneck is the computational powerrequired for the simulation, that dictates the smallest element size possible to use.In our simulation we used the Global Element Size of 2.5 m in Abaqus. In order toget an idea how much the mesh size affects the simulation accuracy an additionalsimulation was performed using Global Element Size of 4.0 m.

The difference we observed when using a larger element size was that maximumprincipal stresses and minimal principal stresses had lower maximum values andhigher minimum values. Using a finer mesh, the area with maximum stress will ingeneral be found in a smaller sized mesh element. Therefore, a larger part of thatspecific mesh element will be exerted to a high stress and result in a larger maximumstress in the results.

8.3 Element selection for adding uplift pressure

For modelling the uplift pressure affecting the dam, elements have been selected atbest ability in Abaqus to correspond to the uplift model calculation described inSection 3.5. The volume of the dam that affected by uplift pressure was given re-duced gravitational acceleration. Ideally the process of mirroring the uplift pressuredistribution onto the dam elements should be based on a more empirical methodthan the one used in this study.

8.4 Element selection for sliding stability analysis

A set of elements is individually selected by the user by clicking and marking theelements in Abaqus. This was done for a number of cross-sections before calculatingan average value over all the used cross-sections to retrieve an average K-value for theused external conditions (for the simulation case). The element selection at the basesurface below the dam was made at best ability with the intention to have an elementdistribution that would give data that could analyse the specific cross-section of thedam base accurately.

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9 References

9.1 Main references

An, X., Lee, S., Liu, C. & Ahn, C.R. 2013, ”Life-Cycle Assessment of Concrete DamConstruction: Comparison of Environmental Impact of Rock-Filled and Conven-tional Concrete”, Journal of Construction Engineering and Management, vol. 139,no. 12, pp. A4013009.

An, X., Wu, F., Jin, F., Huang, M., Hu, Z., Chen, C., Liu, C. 2014. ”Rock-filledconcrete, the new norm of SCC in hydraulic engineering in China”. Cem. Concr.Compos., 54 (2014), pp 89-99.

Boberg, B & Holm, D (2012) “FEM modeling of concrete gravity dams”, TRITALWR Degree Project 12:09 23 pages, pp 12-13.

Hennig, T., Wang, W., Feng, Y., Ou, X. & He, D. 2013, ”Review of Yunnan’shydropower development. Comparing small and large hydropower projects regardingtheir environmental implications and socio-economic consequences”, Renewable andSustainable Energy Reviews , vol. 27, pp. 585-595.

ICOLD (International comission on large dams). 2015. ”From Masonry to Rock-fillconcrete dam”, ICOLD Technical Commitee on Cemented Material Dams.

Jansen, R.B. 1988, Advanced Dam Engineering for Design, Construction, and Re-habilitation, 1st edn, Van Nostrand Reinhold, New York.

Liu, Z. 2013, Electric power and energy in China, 1st edn, Wiley, Singapore.

Lundell, D. 2009, ”Rock-fill concrete in Hydraulic Structures”Master thesis in Geoand Water Engineering program, Chalmers University

Ministry of Water Resources & Electric Power of P.R.C. 1979. Specifications forseismic design of hydraulic structures (SDJ 10-78). China WaterPower Press, Bei-jing.

Ministry of Water Resources & Electric Power of P.R.C. 1984. Supplementary pro-visions of Design specification for concrete gravity dams (SDJ 21-78). China Water-Power Press, Beijing.

Okamura, H. & Ouchi, M. 2003, ”Self-Compacting Concrete”, Journal of AdvancedConcrete Technology, vol. 1, no. 1, pp. 5-15.

USACE (U. S. Army Corps Of Engineers). 1995. Gravity Dam Design, EM 1110-2-2200. University Press Of The Pacific. 100 p.

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9.2 Other references

Feng, Jin: Professor at the department of hydraulic engineering, Tsinghua Univer-sity, Beijing. Personal communication March 2016 to June 2016.

Wang, Yiyang : PhD student at the department of hydraulic engineering, TsinghuaUniversity, Beijing. Personal communication March 2016 to June 2016.

WEBSITES: ”ABAQUS 6.9 User Documentation”. textitInternet Manual. Simu-lia. Retrieved 28 April 2016. Available from: http://abaqusdoc.ucalgary.ca/v6.9/books/usi/default.htm

d-maps. 2007. d-maps. [ONLINE] Available at: http://www.d-maps.com/. [Ac-cessed 20 May 2016].

National Bureau of Statistics of China. 2012. China stastical yearbook. [ONLINE]Available at: http://www.stats.gov.cn/. [Accessed 25 May 2016].

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Appendix

Project preparations

Background on rock-filled concrete method

When starting the project it was necessary to receive background knowledge in thearea. In an attempt to understand the rock-filled concrete method we gatheredmaterial and did background reading in the field. This information provided knowl-edge on how this method has been applied in various dam construction throughoutChina during the past years. Additionally, the information provided a view on pos-itive and negative aspects on using this method comparing to conventional concreteconstruction methods.

Learning Abaqus

Model simulations were performed in Abaqus software. At the start of the projectvarious tutorials was used to get familiar with the software. By following thesetutorials step-by-step, an understanding of Abaqus and its features was gained.

Translation of technical descriptions

Technical descriptions for the Songlin rock-filled concrete gravity dam was onlyavailable in a chinese language version. Translation work of the technical descriptionswas therefore required to retrieve the necessary dimensional data for creating thedam model in Abaqus.

Model design procedure

The model design was partly done in Abaqus cae-environment and partly done inUltraEdit by editing an .inp-file that was created from the .cae-model.

Designing in Abaqus

Part: Add structure features based on the dam drawings. Use solid/cut-extrude tocreate an accurate model.

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Material: Define used materials: C15 RFC, C20 SCC, ground rock with its param-eters for Young’s modulus, Poisson’s ratio and material density.

Section: Divide the defined part into different sections. Each section can be givenits respective parameter values. The model for Songlin dam has four sections.

Section Assignment: Connect each of the defined sections to a defined material.

Sets: In order to set boundary constraints for the ground movement, sets for sur-faces that require movement limitations are to be identified. Used for selecting theelements that are to be affected by uplift pressure.

Surfaces: Specifying the surfaces that is to be applied a load.

Designing in UltraEdit

After building the .cae-model in Abaqus, an input-file was written for editing inUltraEdit.

Ground model:

Remove the dam from the model using *MODEL, REMOVE. Simulate the initialground tension by applying gravity to the dead load rock foundation elements. Savethe ground tension results in an .rpt-file and use this as an initial conditions in thesimulations where the dam is present.

Initial conditions: Initial ground tension is used as an initial condition in themodels where the dam is present.

Model gravity: Introduce the dam to the model. Apply gravitational force tothe dead load of the dam sections and the rock foundation.

Boundary conditions: The dam and the rock foundation are given movementrestrictions.

Steps:

• Geostatic step

• Hydrostatic-and vertical water pressure step.

• Uplift pressure step

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Input-file for model

Figure 9.1: Input-file for sections, materials and boundary conditions for checkflood load case.

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Figure 9.2: Input-file for initial conditions and steps for check flood load case.

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