basic design report · 11/11/2019 · b1.1: drainage failure + low tailwater. upstream water level...

BASIC DESIGN REPORT

11500292411 November 2019

Rev 0

LUANG PRABANG POWER COMPANY LIMITEDLuang Prabang HPP

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Luang Prabang HPP – Basic Design Report 1150002924Structural Analysis Report i

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Contact

Pöyry Energy Ltd. (Thailand)Vanit II Bldg, 22nd Floor, Room#2202 - 22041126/2 New Petchburi RoadMakkasan, RajchthewiTH-10400 BANGKOKThailandTel. +66 2 108 1000

Robert Braunshofer, Business ManagerMobile: +66 92 264 [email protected]

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Luang Prabang HPP – Basic Design Report 1150002924Structural Analysis Report ii


“This report has been prepared by Pöyry Energy Ltd. (“Consultant”) for Luang PrabangPower Company Limited (“Client”, “LPCL”) pursuant to the Contract signed betweenthem (“Agreement”). This report is based in part on information not within Pöyry’scontrol. Surveys have been executed by subcontractors and information were providedto Poyry confirmed to be correct.While the information provided in this report is believed to be accurate and reliableunder the conditions and subject to the qualifications set forth herein Pöyry does not,without prejudice to Pöyry’s obligations towards the Client under the Agreement, makeany representations or warranties, expressed or implied, as to the accuracy orcompleteness of such information.

Use of this report and any of the estimates contained herein by anyone else than theClient (“Third Party User”) shall therefore be at the Third Party User’s sole risk. Anyuse by a Third Party User shall constitute a release and agreement by the Third PartyUser to defend and indemnify Pöyry from and against any liability of Pöyry, whatsoeverin type or nature, in connection with such use, whether liability is asserted to arise incontract, negligence, strict liability or other theory of law.

All information contained in this report is of confidential nature and may be used anddisclosed by the Client solely in accordance with the terms and conditions set forth inthe Agreement.”

All rights are reserved. This document or any part thereof may not be copied orreproduced without permission in writing from Pöyry Energy Ltd.

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Luang Prabang HPP – Basic Design Report 1150002924Structural Analysis Report i


Table of Contents

1 PURPOSE AND SCOPE ................................................................................................... 1

1.1 Introduction ......................................................................................................................... 11.2 Codes and Standards ............................................................................................................ 21.3 Other References ................................................................................................................. 21.4 Dam Safety – Performance Criteria ...................................................................................... 2

2 POWERHOUSE ................................................................................................................ 3

2.1 General ................................................................................................................................ 32.2 Structure Layout .................................................................................................................. 32.3 Performance Criteria ............................................................................................................ 42.4 Foundation ........................................................................................................................... 52.5 Material ............................................................................................................................... 52.6 Design Loads ....................................................................................................................... 52.6.1 Dead Load ........................................................................................................................... 52.6.2 Live Load ............................................................................................................................ 62.6.3 Water Levels ........................................................................................................................ 62.6.4 Seismic Load ....................................................................................................................... 62.7 Load Cases .......................................................................................................................... 62.8 Design Method .................................................................................................................... 92.8.1 Stability Analysis ................................................................................................................. 92.8.2 Structural Verification.......................................................................................................... 92.9 Stability Analysis ................................................................................................................. 92.9.1 Geometry ............................................................................................................................. 92.9.2 Calculation of Uplift Pressures ........................................................................................... 102.9.3 Rock Mass below Foundation ............................................................................................ 102.9.4 Upstream Hydrostatic Pressure .......................................................................................... 102.9.5 Permanent Sliding Calculations.......................................................................................... 112.9.6 Results of the Stability Analysis ......................................................................................... 112.9.7 Conclusion ......................................................................................................................... 132.10 Structural Verification of the Powerhouse Structure ........................................................... 132.10.1 General .............................................................................................................................. 132.10.2 Structural Model ................................................................................................................ 142.10.3 Results of the Structural Verification ................................................................................. 14

3 SPILLWAY ...................................................................................................................... 15

3.1 General .............................................................................................................................. 153.2 Structure Layout ................................................................................................................ 163.3 Performance Criteria .......................................................................................................... 173.4 Foundation ......................................................................................................................... 173.5 Material ............................................................................................................................. 173.6 Design Loads ..................................................................................................................... 183.6.1 Dead Load ......................................................................................................................... 183.6.2 Live Load .......................................................................................................................... 183.6.3 Water Levels ...................................................................................................................... 183.6.4 Seismic Load ..................................................................................................................... 193.7 Load Cases ........................................................................................................................ 193.8 Design Method .................................................................................................................. 21

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Luang Prabang HPP – Basic Design Report 1150002924Structural Analysis Report ii


3.8.1 Stability Analysis ............................................................................................................... 213.8.2 Structural Verification........................................................................................................ 223.9 Stability Analysis ............................................................................................................... 223.9.1 Geometry ........................................................................................................................... 223.9.2 Calculation of Uplift Pressures ........................................................................................... 233.9.3 Inclination of Sliding Surface ............................................................................................. 233.9.4 Rock Mass below Foundation ............................................................................................ 233.9.5 Siltation ............................................................................................................................. 243.9.6 Dynamic Excitation ........................................................................................................... 243.9.7 Results of the Stability Analysis ......................................................................................... 253.9.8 Conclusion ......................................................................................................................... 273.10 Structural Verification of the Spillway Structure ................................................................ 273.10.1 Structural Model ................................................................................................................ 273.10.2 Parameters ......................................................................................................................... 283.10.3 Temperature ....................................................................................................................... 283.10.4 Safety Evaluation Earthquake (SEE) .................................................................................. 293.10.5 Results ............................................................................................................................... 30

4 NAVIGATION LOCK..................................................................................................... 31

4.1 General .............................................................................................................................. 314.2 Structure Layout ................................................................................................................ 314.3 Performance Criteria .......................................................................................................... 324.4 Foundation ......................................................................................................................... 324.5 Material ............................................................................................................................. 324.6 Design Loads ..................................................................................................................... 334.6.1 Dead Load ......................................................................................................................... 334.6.2 Live Load .......................................................................................................................... 334.6.3 Water Levels ...................................................................................................................... 334.6.4 Backfill Loads ................................................................................................................... 344.6.5 Seismic Load ..................................................................................................................... 344.7 Load Cases ........................................................................................................................ 344.8 Design Method .................................................................................................................. 374.8.1 Stability Analysis ............................................................................................................... 374.8.2 Structural Verification........................................................................................................ 374.9 Stability Analysis ............................................................................................................... 374.9.1 Geometry ........................................................................................................................... 374.9.2 Calculation of Uplift Pressure ............................................................................................ 384.9.3 Backfill Water Level .......................................................................................................... 384.9.4 Results of the Stability Analysis ......................................................................................... 384.9.5 Conclusion ......................................................................................................................... 384.10 Structural Verification of the Navigation Lock Structure .................................................... 394.10.1 Structural Model ................................................................................................................ 394.10.2 Results of the Structural Verification ................................................................................. 39

5 RCC CLOSURE STRUCTURE ...................................................................................... 40

5.1 General .............................................................................................................................. 405.2 Structure Layout ................................................................................................................ 405.3 Performance Criteria .......................................................................................................... 415.4 Foundation ......................................................................................................................... 415.5 Material ............................................................................................................................. 415.6 Design Loads ..................................................................................................................... 41

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Luang Prabang HPP – Basic Design Report 1150002924Structural Analysis Report iii


5.6.1 Dead Load ......................................................................................................................... 425.6.2 Live Load .......................................................................................................................... 425.6.3 Water Levels ...................................................................................................................... 425.6.4 Backfill load ...................................................................................................................... 435.6.5 Seismic Load ..................................................................................................................... 435.7 Load Cases ........................................................................................................................ 435.8 Design Method .................................................................................................................. 455.9 Stability Analysis ............................................................................................................... 455.9.1 Geometry ........................................................................................................................... 455.9.2 Calculation of Uplift Pressures ........................................................................................... 465.9.3 Inclination of Sliding Surface ............................................................................................. 475.9.4 Backfill Loads ................................................................................................................... 475.9.5 Results of the Stability Analysis ......................................................................................... 475.9.6 Conclusion ......................................................................................................................... 485.10 Stress Analysis of the RCC Closure Structure .................................................................... 49

6 RIGHT PIER ................................................................................................................... 50

6.1 General .............................................................................................................................. 506.2 Analogy Comparison ......................................................................................................... 506.3 Results ............................................................................................................................... 516.4 Conclusion ......................................................................................................................... 52

7 LEFT PIER ...................................................................................................................... 53

7.1 General .............................................................................................................................. 537.2 Analogy Comparison ......................................................................................................... 537.3 Results ............................................................................................................................... 547.4 Conclusion ......................................................................................................................... 55

ANNEXES FOR STRUCTURAL ANALYSIS REPORT............................................................ 56

ANNEX 1. LOAD CASES .................................................................................................. 57

ANNEX 2-1 POWERHOUSE – STABILITY CALCULATION ........................................ 58

ANNEX 2-2 POWERHOUSE – PERMANENT SLIDING CALCULATIONS ................. 59

ANNEX 2-3 POWERHOUSE – STRUCTURAL VERIFICATION ................................... 60

ANNEX 3-1 SPILLWAY – STABILITY CALCULATIONS .............................................. 61

ANNEX 3-2 SPILLWAY – STRUCTURAL VERIFICATION .......................................... 62

ANNEX 4-1 NAVIGATION LOCK – STABILITY CALCULATIONS ............................ 63

ANNEX 4-2 NAVIGATION LOCK – STRUCTURAL VERIFICATION ......................... 64

ANNEX 5-1 RCC CLOSURE STRUCTURE – STABILITY CALCULATIONS.............. 65

ANNEX 5-2 RCC CLOSURE STRUCTURE – PERMANENT SLIDINGCALCULATIONS ........................................................................................................... 66

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Luang Prabang HPP – Basic Design Report 1150002924Structural Analysis Report iv


List of Figure

Figure 1-1: Main Structures of Luang Prabang HPP ................................................................ 1Figure 2-1: Section through the Powerhouse ........................................................................... 3Figure 2-2: Earthquake designation at Powerhouse section 1-1 ............................................... 4Figure 2-3: LC A1.1 - Normal + low tailwater ........................................................................ 7Figure 2-4: LC A2 - Maintenance + low tailwater ................................................................... 7Figure 2-5: LC B1.1 – Drainage failure + low tailwater .......................................................... 7Figure 2-6: LC C1.1 - PMF ..................................................................................................... 8Figure 2-7: LC C3 – Seismic load case (SEE) ......................................................................... 8Figure 2-8: LC C5 –Surcharge ................................................................................................ 8Figure 2-9: Typical Powerhouse section ................................................................................. 9Figure 2-10: Rock mass below foundation .............................................................................. 10Figure 2-11: Hydrostatic water pressure .................................................................................. 11Figure 2-12: Permanent sliding displacements (Powerhouse founded on sediment- siltsone &shale) 13Figure 2-13: FE-model of the LP HPP Powerhouse ................................................................ 14Figure 3-1: Section through the Surface Spillway bay ........................................................... 15Figure 3-2: Section through the Low Level Outlet Spillway bay ........................................... 16Figure 3-3: Spillway boundaries ........................................................................................... 17Figure 3-4: LC A1.1 – Normal + low tailwater...................................................................... 19Figure 3-5: LC B1.1 – Maintenance + low tailwater .............................................................. 20Figure 3-6: LC B2.1 – Drainage failure + low tailwater ........................................................ 20Figure 3-7: LC C1.1 – PMF .................................................................................................. 20Figure 3-8: LC C3 – Seismic load case (SEE) ....................................................................... 21Figure 3-9: LC C4 – Surcharge ............................................................................................. 21Figure 3-10: Analysis section of the low level outlet ............................................................... 22Figure 3-11: Analysis section of the Surface Spillway ............................................................ 23Figure 3-12: Inclination of sliding surface............................................................................... 23Figure 3-13: Rock mass below foundation .............................................................................. 24Figure 3-14: Possible Siltation is front of the Spillway ............................................................ 24Figure 3-15: Right Spillway model ......................................................................................... 27Figure 3-16: Left Spillway model ........................................................................................... 28Figure 3-17: EC design spectrum parameter............................................................................ 29Figure 3-18: SEE Design Spectra compared with response spectra defined in SHA ................ 30Figure 3-19: Masses considered for the earthquake design analysis ......................................... 30Figure 4-1: Layout of the Navigation Lock ........................................................................... 31Figure 4-2: Backfill at the Navigation Lock .......................................................................... 34Figure 4-3: LC A1.1 – Normal + low lock level .................................................................... 35Figure 4-4: LC B1.1 – Maintenance (lock empty) ................................................................. 35Figure 4-5: LC B2.1 – Drainage failure + low lock level ....................................................... 35Figure 4-6: LC B4 – Construction ......................................................................................... 36Figure 4-7: LC C1.1 – PMF .................................................................................................. 36Figure 4-8: LC C3 – Seismic load case (SEE) ....................................................................... 36Figure 4-9: Analysis section of the upper lock chamber ........................................................ 37Figure 4-10: FE-model of the LP HPP Navigation Lock ......................................................... 39Figure 5-1: RCC-Dam Geometry Parameters ........................................................................ 40Figure 5-2: Backfill at the RCC Closure Structure ................................................................ 43Figure 5-3: LC A1.1 – Normal + low tailwater...................................................................... 44Figure 5-4: LC B1.1 – Drainage failure + low tailwater ........................................................ 44Figure 5-5: LC B2.1 – Sediment dredging failure + low tailwater ......................................... 44Figure 5-6: LC C1.1 – PMF .................................................................................................. 45Figure 5-7: LC C3 – Seismic load case (SEE) ....................................................................... 45

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Luang Prabang HPP – Basic Design Report 1150002924Structural Analysis Report v


Figure 5-8: Typical RCC Closure Structure section ............................................................... 46Figure 5-9: Hydrostatic Loads and Uplift Pressure ................................................................ 46Figure 5-10: Static Backfill Loads .......................................................................................... 47Figure 5-11: Permanent Sliding displacements (the RCC Closure Structure) ........................... 48Figure 6-1: Dimensions of the dam-safety relevant part of the Right Pier .............................. 50Figure 7-1: Dimensions of the dam-safety relevant part of the Left Pier ................................ 53

List of Table

Table 2-1: PH blocks and main elevations ............................................................................. 4Table 2-2: Shear strength parameters for sliding stability (Powerhouse) ................................ 5Table 2-3: Dead load ............................................................................................................. 5Table 2-4: Design elevations for the Upstream water levels ................................................... 6Table 2-5: Tailrace water levels ............................................................................................. 6Table 2-6: Seismic loads ........................................................................................................ 6Table 2-7: Results of the Stability Analysis for the Powerhouse – Sediment – Siltstone &Shale 12Table 2-8: Results of the Stability Analysis for the Powerhouse – Volcanic basaltic andesite

12Table 3-1: Design Parameters of the Spillway of LP HPP .................................................... 15Table 3-2: SP parts and main elevations .............................................................................. 16Table 3-3: Shear strength parameters for sliding stability (Spillway) ................................... 17Table 3-4: Dead load ........................................................................................................... 18Table 3-5: Design elevations for the Upstream water levels ................................................. 18Table 3-6: Tailrace water levels ........................................................................................... 19Table 3-7: Seismic loads ...................................................................................................... 19Table 3-8: Calculation of the overall acceleration using the RSA for the FE model.............. 25Table 3-9: Results of the Stability Analysis for the Surface Spillway ................................... 26Table 3-10: Results of the Stability Analysis for the Low Level Outlet .................................. 26Table 3-11: FE model paramter ............................................................................................. 28Table 3-12: Parameters for the design response spectra used for the Spillway design ............. 29Table 4-1: Upper lock blocks ............................................................................................... 32Table 4-2: Shear strength parameters for sliding stability (Navigation Lock) ....................... 32Table 4-3: Dead load ........................................................................................................... 33Table 4-4: Design elevations for the reservoir water levels .................................................. 33Table 4-5: Tailrace water levels ........................................................................................... 34Table 4-6: Seismic loads ...................................................................................................... 34Table 4-7: Results of the Stability Analysis for the Navigation Lock ................................... 38Table 5-1: PC blocks and main elevations ........................................................................... 41Table 5-2: Shear strength parameters for sliding stability ..................................................... 41Table 5-3: Dead load ........................................................................................................... 42Table 5-4: Design elevations for the Upstream water levels ................................................. 42Table 5-5: Tailrace water levels ........................................................................................... 42Table 5-6: RCC Clousre Sturcture backfill elevations .......................................................... 43Table 5-7: Seismic loads ...................................................................................................... 43Table 5-8: Backfill properties .............................................................................................. 47Table 5-9: Results of the Stability Analysis for the Low Level Outlet .................................. 48Table 6-1: Analogy between the Right Pier and the right side of the Powerhouse ................ 51Table 7-1: Analogy between the Left Pier and the left side of the Powerhouse ..................... 54

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Luang Prabang HPP – Basic Design Report 1150002924Structural Analysis Report 1


1 PURPOSE AND SCOPE

1.1 IntroductionThe purpose of the present document is to summarize the performed civil basic designof the water retaining structures of the Luang Prabang Hydroelectric Power Project (LPHPP). The civil design includes the stability analysis and the structural verification ofimportant structural members for the following structures:

· Powerhouse (PH)

· Spillway (SP)

· Navigation Lock (NL)

· RCC Closure Structure (RC)The stability of the Right Pier (RP) and the Left Pier (LP) has been proven by analogyconclusion to the Powerhouse.It is understood that the basic design summarized in the present report is based on thedata and general requirements known in September 2019, and may be subject toadjustments as new information and updated requirements will become available. Theboundary conditions, design requirements, design principles and the applicable loads aredefined in the Design Criteria report. The civil design is performed according tointernational standards and the Lao Electric Power Technical Standard (LEPTS) asfurther defined in the Design Criteria report.

The design of the cofferdams, the foundation treatment as well as the design of theexcavation and slopes is presented in other reports.

Figure 1-1: Main Structures of Luang Prabang HPP

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1.2 Codes and StandardsThe LP HPP shall be designed in accordance with the most recognized internationalstandards and complies with the Lao Electric Power Technical Standard (LEPTS).Further information is given in the Design Criteria.

· ICOLD: International Commission on Large Dams: Guidelines

· USACE: United States Army Corps of Engineers: Engineering Manuals

· ACI: American Concrete Institute: ACI 318

· ASCE: American Society of Civil Engineers: ASCE 7

· FEMA: Federal Emergency Management Agency: Guidelines

· LEPTS: Lao Electric Power Technical Standard

· MRC: Mekong River Commission

1.3 Other ReferencesReference is made to the Design Criteria report where the basic design assumptions andloads are summarized. The findings and parameters from other studies such as theseismic hazard assessment or the geotechnical report are also summarized in the DesignCriteria report.

· Luang Prabang HPP, Design Criteria (Revision 0 dated on 04.10.2019)

1.4 Dam Safety – Performance CriteriaThe structures dealt with in this report are dam-safety relevant structures. The SafetyGuidelines issued by the International Committee on Large Dams (ICOLD) give thefollowing performance criteria under the probable maximum flood (PMF) and the safetyevaluation earthquake (SEE) loading:

· The structures are flood-safe during the probable maximum flood (PMF).Therefore the access to the interior of the structures (i.e. Powerhouse and allgalleries) is above the PMF level in the LP HPP.

· Following the 475 years’ Operating Basic Earthquake (OBE), there should eitherbe no damage or minor repairable damage.

· During and after the Safety Evaluation Earthquake (SEE), damage is allowable,but it must not lead to catastrophic failure or uncontrolled release of thereservoir. According to the USACE, damage also includes permanent slidingdisplacements in the stability analysis and inelastic deformations in the structuraldesign considered with the demand capacity ratio (DCR) approach.

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2 POWERHOUSE

2.1 GeneralThe Luang Prabang Powerhouse (PH) is located within the Mekong mainstream andforms part of the water retaining structures. Therefore, the Powerhouse must fulfil allrequirements that are applicable to a dam at that location. This includes the ProbableMaximum Flood (PMF) and the Safety Evaluation Earthquake (SEE) which is thegoverning load case for the stability analysis and the structural design.The principal arrangement of the Powerhouse comprises of a central part formed by thePowerhouse structure with the seven (7) vertical Kaplan units (main units, 200 MW and765 m3/s each) and the auxiliaries, and an erection bay at each end of the Powerhouse(including unloading bays above the erection bay at each end). The erection bay conceptallows simultaneous assembly of three (3) rotors.

Bridges and access platforms over the entire length of the Powerhouse will be provided.Further the upstream and downstream fish migration system is integrated in thePowerhouse structure, with the collector system on the upstream side (downstreammigration) and downstream (upstream migration).

Figure 2-1: Section through the Powerhouse

2.2 Structure LayoutThe Powerhouse is a reinforced Conventional Vibrated Concrete (CVC) structurefounded on solid rock. All forces, mainly horizontal forces in flow direction, aretransmitted within the structure to the bottom of the foundation where they will betransmitted to the rock.The section of the Powerhouse can be roughly divided into three main sections:upstream with the trashrack, maintenance stoplogs and the intake gates, central with theturbines and generator and downstream with the BoP rooms and the draft tube. Themachine hall is covered with a steel roof.The Powerhouse is separated with flow parallel contraction (movement) joints into threeblocks, not counting the two erection bays.

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Table 2-1: PH blocks and main elevations

Block number and units Width xlengthfoundation

Foundation

Block 1: unit 1 & 2 71.5m x 95.7m Volcanic basaltic andesite

Block 2: unit 3, 4 & 5 99.0m x 95.7m Sediment-siltstone & shale

Block 3: unit 6 & 7 67.0m x 95.7m Sediment-siltstone & shale

Main elevations

Foundation 238.0 m asl

Draft tube sill 246.0 m asl

Intake slab 265.0 m asl

Unit axis 266.92 m asl

Machine Hall 283.20 m asl

Downstream deck 310.0 m asl

Upstream deck 317.0 m asl

2.3 Performance CriteriaThe Powerhouse is a dam-safety relevant structure and must resist the SEE earthquakewithout uncontrolled release of reservoir. This is given when the red marked area inFigure 2-2 does not fail and the upstream power intake gate remains operational.

For the stability analysis, permanent sliding displacements are allowed but shall remainin reasonable range, which is defined in the Design Criteria. For the structural design,the deformations must not remain in the elastic range and the demand capacity ratioconcept is permitted.

For the civil design, the Powerhouse can be divided as follows:

· Dam safety relevant: SEE

· Non-dam safety relevant: MDE

Figure 2-2: Earthquake designation at Powerhouse section 1-1

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2.4 FoundationThe resistance against sliding is determined for the LEPTS load cases considering thefriction angle and the cohesion, whereas for the USACE the cohesion has beenneglected, except for the SEE load case.Table 2-2: Shear strength parameters for sliding stability (Powerhouse)

PowerhouseRock type in contact zone

c [MPa] φs [°]1 φd [°]2

Volcanic – Basaltic Andesite 0.19 50 30*

Sediment - Siltstone & Shale 0.08 42 25*

* assumption c=0 for τ(φd) residual, 1 σ1=750 kPa; 2 average value

2.5 MaterialThe Spillway consists of C25 Conventional Vibrated Concrete (CVC) with fc’=25 MPa.Other concrete classes are not considered for the basic design stability analysis andreinforcement verification.

2.6 Design LoadsReference is made to the Design Criteria report for a more detailed definition of thedesign requirements, design principles and the loads. This chapter only summarizes themain loads.The following loads have been considered for the structural design of the spillway:

· Dead Load of the Concrete Structure and water

· Live loads

· Equipment Loads

· Hydrostatic Loads

· Uplift

· Seismic Loads

2.6.1 Dead LoadThe weight of the concrete is considered as indicated below for the stability analysis.For the structural verification, the weight is considered in the FE model.

Water dead loads within the limits of the structural wedge depend on the load case(water level) and are not listed herein but considered in the calculations.Table 2-3: Dead load

Concrete dead load Value

Concrete volume (unit 2) 104’480 m3

Unit weight concrete (stability analysis) 24 kN/m3

Unit weight concrete (structural verification) 25 kN/m3

Equipment load (Turbine, Generator) 18’335 kN

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2.6.2 Live LoadNot considered for the stability analysis.

For the structural verification according to the Design Criteria report.

2.6.3 Water LevelsThe following upstream water levels have been considered.Table 2-4: Design elevations for the Upstream water levels

Upstream water level Value Type

Design Full Supply Level (FSLD) 312.50 m a.s.l. Normal

PMF Level (Q=41’400 m3/s) 314.20 m a.s.l. Extreme

Maximum considered surcharge 317.00 m a.s.l. Extreme

The tailrace water level which have been considered for the stability analysis areTable 2-5: Tailrace water levels

Tailrace water level Tailwater Level Type

Minimum Operating Level (MOL, Q=745 m3/s) 275.50 m a.s.l. Normal

Coincident pool / median flow (Q=2’100 m3/s) 278.80 m a.s.l.

10-year flood (Q=18’200 m3/s) 292.60 m a.s.l. Normal

1000-year flood (Q=23’800 m3/s) 295.30 m a.s.l.

PMF level (Q=41’400 m3/s) 300.50 m a.s.l. Extreme

2.6.4 Seismic LoadThe following seismic loads have been considered.Table 2-6: Seismic loads

Design Earthquake Return Period PGA [g]

Horizontal Vertical

SEE Safety Evaluation Earthquake --- (DSHA) 0.49 0.40

OBE Operating Basis Earthquake 145 years 0.13 0.10

The three scaled accelerograms (time histories) show horizontal accelerations in twoorthogonal directions: hor.360° and hor.90° resulting in 3×2=6 seismic combinations forboth foundation types for the SEE load case. All 2×6=12 combinations wereinvestigated for the SEE load case.

2.7 Load CasesThe detailed load cases are defined in Annex 1. The below figures show some of theapplied load cases.

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Figure 2-3: LC A1.1 - Normal + low tailwater

Figure 2-4: LC A2 - Maintenance + low tailwater

Figure 2-5: LC B1.1 – Drainage failure + low tailwater

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Figure 2-6: LC C1.1 - PMF

Figure 2-7: LC C3 – Seismic load case (SEE)

Figure 2-8: LC C5 –Surcharge

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2.8 Design Method

2.8.1 Stability AnalysisThe stability analysis calculation for the Powerhouse has been carried out using Excel,resulting in forces and safety factors for static and pseudo-static load combinations.

Two sections with different foundation properties according to chapter 2.4 representingthe two main bedrock types were analysed. The load cases and the applied loads are thesame for both investigated sections. The applied forces and the dead loads are for oneentire unit from the contraction joint till the limit with the next unit with a width of33.50 m.To evaluate the permanent sliding displacements, the computer program RS-DAM hasbeen used. The RS-DAM uses the scaled accelerograms (time histories) as input andone set of foundation properties

2.8.2 Structural VerificationFor the structural verification, a FE-model has been used. The governing SEE load casehas been calculated with a time-history analysis.

2.9 Stability Analysis

2.9.1 GeometryThe concrete volume for the 33.50 m wide unit 2 block is given in chapter 2.6.1.

Figure 2-9: Typical Powerhouse section

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2.9.2 Calculation of Uplift PressuresFor the uplift pressures the effect of the grout curtain and drainage gallery is considered.The reduction in uplift pressures is estimated with a drainage efficiency of 35% asdefined in the Design Criteria. A separate unusual load case for drainage failure isconsidered in the stability analysis as well.Only for the SEE load case, the drainage efficiency was assumed with 50%.

2.9.3 Rock Mass below FoundationTwo rock mass volumes that are completely surrounded by the CVC structure areconsidered as additional mass for the sliding stability analysis. In the earthquake loadcases the rock mass below foundation is also subjected to horizontal and verticalaccelerations.Horizontal bearing resistance of the rock mass in the tailrace excavation downstream ofthe Powerhouse and at the steep slope below the draft tube is not considered.The rock parameters for the additional rock weight are as follows:

· Rock mass volume (total): V = 4’236 m3

· Rock mass buoyant unit weight g = 16 kN/m3

Figure 2-10: Rock mass below foundation

2.9.4 Upstream Hydrostatic PressureThe upstream hydrostatic pressure acting towards downstream has been applied fromthe corresponding reservoir water level till the lowest point of the foundation which is inthe centre part of the Powerhouse, below the draft tubes. A considerable portion of thatpressure however lies downstream of the grout curtain and the drainage holes thatreduce the uplift pressure as defined in chapter 2.9.2. The same reduction also applies tothe horizontally acting hydrostatic water pressure between the bottom of the upstreamgallery at elevation +254.0 m asl and the deepest point of the Powerhouse at elevation+238.0 m asl.For P

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Figure 2-11: Hydrostatic water pressure

2.9.5 Permanent Sliding CalculationsThe permanent sliding displacements were calculated with the computer program RS-DAM that calculates the displacements for each time step in a time-history analysis.

Because of the characteristic of the program that jumps back to the static friction angleas soon as the sliding safety factor is above 1.0, the residual friction angle has been usedas static friction angle as well. The cohesion is set by default as c=0 kPa. This approachoverestimates the sliding displacements because the initial sliding starts much earlierthan with the static foundation shear parameter. For this reason, an additionalverification with the static shear parameter has been done.

Further information is given in Annex 2-2.

2.9.6 Results of the Stability AnalysisThe civil structures shall be designed to be safe against sliding, floatation, overturningand foundation bearing. The results of stability analysis are presented below:

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Table 2-7: Results of the Stability Analysis for the Powerhouse – Sediment –Siltstone & Shale

Table 2-8: Results of the Stability Analysis for the Powerhouse – Volcanic basalticandesite

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[-] [-] [%] [-] [%] [%] [-] [-] [kPA] [kPA] [kPA]

A1.1_normal situation_USUAL 2.42 2 0.00 Middle third = L/6= 100 100 2.21 1.3 865 183 9000

A1.2_normal situation_USUAL + HQ10 3.27 2 0.00 Middle third = L/6= 100 100 1.75 1.3 620 197 9000

A2_maintainance_USUAL + low waterlevel 2.08 2 0.00 Middle third = L/6= 100 75 2.04 1.3 730 172 9000

B1.1_drainage failure_UNUSUAL + low waterlevel 2.16 1.5 0.00 Middle half = L/4= 100 75 1.96 1.2 860 76 9000

B1.2_drainage failure_UNUSUAL + HQ10 2.58 1.5 0.00 Middle half = L/4= 100 75 1.65 1.2 581 176 9000

B2.1_OBE_UNUSUAL 1.59 1.5 0.00 Middle half = L/4= 94 75 2.02 1.2 1026 -61 9000

C1.1_PMF_EXTREME 3.98 1.1 0.00 In the Base = L/2= 100 >0 1.65 1.1 550 227 9000

C3_SEE_EXTREME 0.39 1.1 0.00 In the Base = L/2= 20 >0 1.88 1.1 1606 -711 9000

C4_post SEE_EXTREME 1.20 1.1 0.00 In the Base = L/2= 100 >0 1.89 1.1 809 93 9000

C5_surcharge_317,00_EXTREME 2.25 1.1 0.00 In the Base = L/2= 100 >0 2.14 1.1 895 127 9000

C6_maintanance_EXTREME + HQ100 2.22 1.1 0.00 In the Base = L/2= 100 >0 1.49 1.1 447 137 9000

A1.3_LEPTS-usual 3 3 100.00 Middle third = L/6= 100 100 2.2 865 183

B3.2_LEPTS-seismic (OBE) 2 2 100.00 Middle half = L/4= 94 75 2.0 1026 -61

C1.2_LEPTS-flood (PMF) 5 2 100.00 Middle half = L/4= 100 75 1.7 550 227

Rotation Flotation Bearing capacitiy

Load case

Sliding

Safe

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[-] [-] [%] [-] [%] [%] [-] [-] [kPA] [kPA] [kPA]

A1.1_normal situation_USUAL 3.20 2 0.00 Middle third = L/6= 100 100 2.21 1.3 865 183 9000

A1.2_normal situation_USUAL + HQ10 4.33 2 0.00 Middle third = L/6= 100 100 1.75 1.3 620 197 9000

A2_maintainance_USUAL + low waterlevel 2.76 2 0.00 Middle third = L/6= 100 75 2.04 1.3 730 172 9000

B1.1_drainage failure_UNUSUAL + low waterlevel 2.86 1.5 0.00 Middle half = L/4= 100 75 1.96 1.2 860 76 9000

B1.2_drainage failure_UNUSUAL + HQ10 3.42 1.5 0.00 Middle half = L/4= 100 75 1.65 1.2 581 176 9000

B2.1_OBE_UNUSUAL 2.10 1.5 0.00 Middle half = L/4= 94 75 2.02 1.2 1026 -61 9000

C1.1_PMF_EXTREME 5.27 1.1 0.00 In the Base = L/2= 100 >0 1.65 1.1 550 227 9000

C3_SEE_EXTREME 0.48 1.1 0.00 In the Base = L/2= 20 >0 1.88 1.1 1606 -711 9000

C4_post SEE_EXTREME 1.49 1.1 0.00 In the Base = L/2= 100 >0 1.89 1.1 809 93 9000

C5_surcharge_317,00_EXTREME 2.98 1.1 0.00 In the Base = L/2= 100 >0 2.14 1.1 895 127 9000

C6_maintanance_EXTREME + HQ100 2.93 1.1 0.00 In the Base = L/2= 100 >0 1.49 1.1 447 137 9000

A1.3_LEPTS-usual 4 3 100.00 Middle third = L/6= 100 100 2.2 865 183

B3.2_LEPTS-seismic (OBE) 3 2 100.00 Middle half = L/4= 94 75 2.0 1026 -61

C1.2_LEPTS-flood (PMF) 7 2 100.00 Middle half = L/4= 100 75 1.7 550 227

Rotation Flotation Bearing capacitiy

Load case

Sliding

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Figure 2-12: Permanent sliding displacements (Powerhouse founded on sediment-siltsone & shale)

2.9.7 ConclusionAs it can be expected, the safety factors for the Powerhouse units founded on sediment-siltstone & shale are considerably lower than for the Powerhouse units founded on thevolcanic basaltic andesite.

The floatation safety factor and the overturning in term of percent of base oncompression and location of resultant are greater than requirement for all load cases.The maximum base pressure is well below the allowable pressure for all load cases.The pseudo-static sliding stability of the Powerhouse is fulfilled for all load casesexcept for the SEE earthquake, which consequences were investigated in the permanentsliding calculations (see Annex 2-2).

Permanent sliding displacements have been estimated to be in the range of 50 cm with aconservative approach. In an optimistic evaluation applying the static shear properties,the permanent sliding displacements tend to zero (range of 2 mm or less). The stabilityrequirements after the SEE event (C4, post SEE) is fulfilled. Because even theoverestimated displacements of 50 cm are acceptable and the effective displacementsare expected to the significantly lower (or even not present), the performance criteria forthe LP HPP Powerhouse are fulfilled.

2.10 Structural Verification of the Powerhouse Structure

2.10.1 GeneralMost of the forces apply at the intake walls from where they are transmitted via theintake slab and the mass concrete around the draft tube to the foundation, or via theMachine Hall floor and the generator barrel to the downstream side of the Powerhouse.A considerable force, also due to the high downstream water level fluctuations, act onthe downstream side of the Powerhouse, which is the reason for the regular pattern ofthe stiffening shear walls within the facility and equipment section of the Powerhouse.Forces at the semi spiral case and the generator foundation remain mainly in the massconcrete in the middle section of the Powerhouse but may lead to high and partiallycomplicated reinforcement arrangements. The design of the different floors of thedownstream BoP rooms, especially the floor below the transformer slab, is governed bythe construction stages, i.e. the fresh concrete weight of the subsequent floor.

C:\ Users\ kch053\ Desktop\ Permanent_Sliding\Sediment_2019_10_02\ LPH

0 5 10 15 20 25 30 35 40 45 50Time (sec)

0.000.05

0.10

0.150.20

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0.350.40

0.450.50

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2.10.2 Structural ModelA finite-element (FE) analysis has been performed for the structural verification of thePowerhouse. Calculations were done either static or as a time-history analysis for theSEE load case. For the time-history analysis, no response modification factor (R-factors) and for the SEE load case, no importance factors Ic are applied.The three sets of time history accelerograms from the seismic hazard assessment areused in the dynamic calculations. For each set of time histories, the 360° orientation wasapplied once into flow direction with the 90° orientation perpendicular to the flow, andonce applied perpendicular to the flow direction with the 90° orientation in flowdirection. These 6 separate calculations were done for both foundation conditions,resulting in 12 separate calculations.

Figure 2-13: FE-model of the LP HPP Powerhouse

2.10.3 Results of the Structural VerificationThe FE-model calculates the required reinforcement for the analyzed load cases.Following the demand capacity ratio (DCR) approach, the reinforcement requirementscalculated in the FE-model can be reduced (manually) because the DCR approach is notpart of the structural building codes and therefore not implemented in the FE analyzingtool.

The results are presented in Annex 2-3.

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3 SPILLWAY

3.1 GeneralDuring flood operation the excess water (water not used for generation of electricityand/or operation of the navigation lock and fish migration Facilities) will be spilledthrough the Spillway (SP). The Spillway structure includes:

· 6 Surface Spillway Bays

· 3 Low Level Outlet BaysThe Spillway is arranged in two main blocks, the first block comprises four (4) SurfaceSpillway Bays and the second block comprises the three (3) Low Level Outlet bays withone Surface Spillway bay on each side (1+1).

The main dimensions of the Spillway bays are given in the following table:Table 3-1: Design Parameters of the Spillway of LP HPP

Surface Spillway Low Level Outlet

Clear width of gate 19.0 m 12.0 m

Clear height of gate 25.0 m 16.0 m

Spillway ogee / LLO sill level 289.0 m asl 275.0 m asl

Capacity per bay (at FSL) 4,850 m3/s 3,530 m3/s

The operation of the Spillway will be such that the first bays in operation will be theLow Level Outlets in order to route “turbidity currents” through the Spillway and tominimize sedimentation in the reservoir area. When the capacity of the Low LevelOutlets is reached the Surface Spillway will start operation. All gates of the SurfaceSpillway will be equipped with flap gates to allow spill of floating debris in front of theSpillway into the tailwater area.

Figure 3-1: Section through the Surface Spillway bay

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Figure 3-2: Section through the Low Level Outlet Spillway bay

3.2 Structure LayoutThe stilling basin is structurally divided by a concrete wall between the two blocks, andis detached from the Spillway by a contraction (movement) joint. The Spillway bridges(upstream and downstream) are embedded in the Spillway piers in order to reasonablylimit the deformations of the piers at the radial gates. To gain additional stiffness, theSpillway is structurally connected to the navigation lock on the right side and to theRight Pier on its left side. The stability analysis however does not rely on thisconnection to the navigation lock or the Right PierTable 3-2: SP parts and main elevations

Block number and units Width x length Foundation

Part 1: 4 Surface Spillways 101.0m x 79.6m Volcanic basaltic andesite

Part 2: 3 LLO & 2 Surface Spillways 104.0m x 76.8m Volcanic basaltic andesite

Main elevations

LLO foundation (at gallery) 256.22 m asl (variable)

Surface Spillway foundation 259.05 m asl (variable)

Surface Spillway ogee 289.0 m asl

Downstream deck 310.0 m asl

Upstream deck 317.0 m aslFor P

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Figure 3-3: Spillway boundaries

3.3 Performance CriteriaThe Spillway structure is a dam-safety relevant structure and must resist the SEEearthquake without uncontrolled release of reservoir.

For the stability analysis, permanent sliding displacements are allowed if not otherwiserestraint. Due to the latera stiffness requirements, the Navigation Lock and the RightPier are structurally connected to the Spillway block. This restrains the displacements inflow direction. Therefore (and considering the fact that the Spillway is located on goodrock), permanent sliding displacements are not permitted for the present configuration.The radial gate must be operational after an SEE event and the deformations of theSpillway piers shall remain elastic, following the limits of the radial gate supplier.Therefore the demand capacity ratio (DCR) approach is not applied to the Spillwaypiers.

3.4 FoundationThe stability analysis design parameters used for the safety factor against sliding arelisted in the table below.

The resistance against sliding is determined for the LEPTS load cases considering thefriction angle and the cohesion, whereas for the USACE the cohesion has beenneglected, except for the SEE load case.Table 3-3: Shear strength parameters for sliding stability (Spillway)

Spillway

Rock type in contact zone

c [MPa] φs [°]1 φd [°]2



3.5 MaterialThe Spillway consists of C25 Conventional Vibrated Concrete (CVC) with fc’=25 MPa.Other concrete classes are not considered for the basic design stability analysis andreinforcement verification.

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3.6 Design LoadsReference is made to the Design Criteria report for a more detailed definition of thedesign requirements, design principles and the loads. This chapter only summarizes themain loads.

The following loads have been considered for the structural design of the Spillway:

· Dead Load of the Concrete Structure


· Uplift

· Earthquake Loads

3.6.1 Dead LoadThe weight of the concrete is considered as indicated below for the stability analysis.For the structural verification, the weight is considered in the FE model.Water dead loads within the limits of the structural wedge depend on the load case(water level) and are not listed herein but considered in the calculations.Table 3-4: Dead load


Concrete volume Surface Spillway (width 24m incl. pier) 34,195 m3

Concrete volume LLO (width 17m incl. pier) 39,677 m3



Equipment load (radial gate, stoplog) Not considered

3.6.2 Live LoadNot considered for the stability analysis.For the structural verification according to the Design Criteria report.

3.6.3 Water LevelsThe following upstream water levels have been considered.Table 3-5: Design elevations for the Upstream water levels


Design Full Supply Level (FSLD) 312.50 m a.s.l. Normal


Maximum considered surcharge 317.00 m a.s.l. Extreme

The tailrace water level which have been considered for the stability analysis are

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Table 3-6: Tailrace water levels


Minimum Operating Level (MOL, Q=745 m3/s) 275.50 m a.s.l. Normal

Median Annual Discharge (Q=2’100 m3/s) 278.80 m a.s.l. Normal


3.6.4 Seismic LoadThe following seismic loads have been considered:Table 3-7: Seismic loads


Horizontal Vertical




Figure 3-4: LC A1.1 – Normal + low tailwaterFor P

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Figure 3-5: LC B1.1 – Maintenance + low tailwater

Figure 3-6: LC B2.1 – Drainage failure + low tailwater

Figure 3-7: LC C1.1 – PMF

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Figure 3-9: LC C4 – Surcharge

3.8 Design Method

3.8.1 Stability AnalysisThe stability analysis calculation for the Spillway was carried out using Excel, resultingin forces and safety factors for static and pseudo-static load combinations.For the response spectra analysis of the stability analysis, the dynamic excitation iscalculated with a FE model (see structural analysis) and its value inserted into the Excelsheet. For further details of the RSA applied for the stability analysis please refer to3.9.6. The finite element model is further explained in chapter 3.10.1.The following load case has been investigated and is only governing for buoyancy /floatation verification.

· Earthquake load combination = +

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3.8.2 Structural VerificationFor the structural verification, a FE-model has been used. The governing SEE load casehas been calculated with a response-spectrum analysis.


3.9.1 GeometryTo prove the stability of the two Spillway blocks, two independent stability analyses forthe Surface Spillway and the LLO have been performed to prove that every section isstable for itself. The connection to the Navigation Lock on the right side and the RightPier on the left side of the Spillway were not taken into account.The analysis is based on one entire Surface Spillway or LLO block including two timeshalf of the pier and a width of 24.0 m (Surface Spillway) and 17.0 m (LLO)respectively. The analysis sections are presented below:

Figure 3-10: Analysis section of the low level outlet

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Figure 3-11: Analysis section of the Surface Spillway

3.9.2 Calculation of Uplift PressuresFor the uplift pressures the effect of the grout curtain and drainage gallery is considered.The reduction in uplift pressures is estimated with a drainage efficiency of 35% asdefined in the Design Criteria. A separate unusual load case for drainage failure isconsidered in the stability analysis as well.

3.9.3 Inclination of Sliding SurfaceThe sliding surface below the rock has an inclination of 1.3° for the Surface Spillwaycross-section and 2.1° for the low level outlet cross-section. The respective inclinationshave been considered in the stability analysis for the sliding stability verification.

Figure 3-12: Inclination of sliding surface

3.9.4 Rock Mass below FoundationThe rock mass below the heel of the foundation has been considered as additional massfor the sliding stability. In the earthquake load cases the rock mass below foundation isalso subjected to horizontal and vertical accelerations.The rock parameters for the additional rock weight are as follows:

· Rock mass volume (Surface Spillway): V = 8’640 m3

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· Rock mass volume (LLO): V = 2’910 m3

· Rock mass buoyant unit weight g = 16 kN/m3

Figure 3-13: Rock mass below foundation

3.9.5 SiltationSiltation in front of the Spillway radial gates has been checked and is considered notcritical for the stability of the structure. This is caused by the favourable effect of the(stabilizing) vertical load in case of siltation providing additional weight for a length ofapproximately 30 m as shown in the sketch below.The favourable effect of stabilizing vertical loads compared to driving horizontal loadsis also valid for earthquake load cases with increased horizontal loads.

Figure 3-14: Possible Siltation is front of the Spillway

3.9.6 Dynamic ExcitationThe input for the RSA used for the stability analysis is based on the FE model furtheroutlined in section 3.10 The natural frequencies, the mobilized mass per naturalfrequency (participation) and the modal reply of the system are calculated in the FEprogram.

Based on the results obtained from the FE analysis the overall acceleration of thestructure considering its actual frequencies is calculated as shown in the table below asan example for the natural frequencies of the Low Level Outlet Structure. In this casethe natural frequency number 4 with a period of 0.275 seconds contributes a significantpart of the mobilized mass in x-direction (flow direction). The number of natural

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frequencies considered must be such, that at least 90% of the mass in the respectivedirection are mobilized. Finally the sum of the spectral accelerations for each mode willdetermine the overall acceleration of the structure considered in the stability analysis(here: 0.25g).Table 3-8: Calculation of the overall acceleration using the RSA for the FE model

Mode ξ (sec) Mx (%) Sx (-) Mx * Sx *ag/ R

1st 0.585 0 0.803 0.000

2nd 0.393 0.2 1.196 0.000

3 0.296 4.2 1.587 0.008

4 0.275 25.7 1.71 0.054

5 0.256 0.2 1.835 0.000

6 0.242 0 1.942 0.000

7 0.231 0.6 2.035 0.001

8 0.226 3.4 2.084 0.009

9 0.22 1.8 2.137 0.005

... 0.216 3.7 2.174 0.010

n

Sum >90% 0.250

ξ... period of natural frequency n

Mx... mobilized mass in flow direction for natural frequency nSx... Normalized response acceleration (modal reply)

ag... Peak Ground Acceleration in the respective direction (here: 0.49)

3.9.7 Results of the Stability AnalysisThe civil structures shall be designed to be safe against sliding, floatation, overturningand foundation bearing. The results of stability analysis are presented below while thedetailed calculation tables are attached in Annex 3-1:

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Table 3-9: Results of the Stability Analysis for the Surface Spillway

Table 3-10: Results of the Stability Analysis for the Low Level Outlet

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3.9.8 ConclusionThe sliding safety factor, floatation safety factor, overturning in term of percent of basein compression and location of resultant, are greater than the requirement for all loadcases. The maximum base pressure is well below the allowable pressure for all loadcases.All the stability criteria are fulfilled.

3.10 Structural Verification of the Spillway StructureThe structural resistance at ultimate limit state of the Spillway pier and Spillway Bridgehave been checked. The results are shown in Annex 3-2.

3.10.1 Structural ModelThe horizontal deformation of the pillar during earthquake is a critical element whichwas investigated specifically in the structural analysis. In order to achieve acceptablepillar deformations perpendicular to the flow it is required to support the pillars of theSurface Spillway with the U/S Spillway Bridge and the D/S Spillway bridgerespectively.The Spillway structure is therefore consisting of two independent structural modelsoutlined below being separated by one deformation joint in the middle of the Spillwaybetween Surface Spillway bay S3 and S2:

Right Spillway Model:Four Surface Spillway bays next to the Navigation Lock.

Figure 3-15: Right Spillway model

Left Spillway Model:Three low level outlet bays with one adjacent Surface Spillway bay on each side.For P

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Figure 3-16: Left Spillway model

The bridge shall be fixed to each pillar forming a continuous beam which is leading to aframe-like structure perpendicular to flow direction subject to less deformation.

3.10.2 ParametersThe parameters shown in the table below were applied for the structural analysis of theSpillway structure. The response modification factor (R-Factor) is depending on theseismic force-resisting system in the respective direction. The seismic force resistingsystem for the Spillway are as follows:

· In Flow Direction: Ordinary Reinforced Concrete Shear Wall

· Perpendicular to Flow: Ordinary Reinforced Concrete Moment Frame

· Vertical Direction: Ordinary Reinforced Concrete Shear WallTable 3-11: FE model paramter

Parameter Value

Design modification factor (flow direction, perpendicular) 1.0

Response Modification Coefficient (R-factor) in flow direction R = 4

Response Modification Coefficient perpendicular to flow R = 3

Response Modification Coefficient vertical R = 4

3.10.3 TemperatureWith the upstream and downstream bridge being fixed to the Spillway pillars the entiresystem will be subjected to thermal movements perpendicular to flow direction. Athermal expansion and contraction equivalent to ±25°C has been considered in thestructural calculation.In case of thermal contraction the induced average tension stresses in the bridge arebelow the tensile strength of the concrete. The bending stresses induced in the pillar arenegligible.

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3.10.4 Safety Evaluation Earthquake (SEE)The structural system described above has been investigated for the load casesconsidered critical. The governing load case for the Spillway pillars is the SEE loadcase with the ground motion accelerations defined in the Design Criteria.

The SEE load case is investigated with a response spectra analysis (RSA). Since thefinite element program does not allow a direct input of the design spectra from theSeismic Hazard Analysis (SHA) the Eurocode Design Spectra was used to obtain asimilar design spectrum. The EC Design spectrum is defined by the followingparameters:

Figure 3-17: EC design spectrum parameter

The parameters used for the EC Spectra shown below were chosen as follows:Table 3-12: Parameters for the design response spectra used for the Spillway design

Parameter of Design Response Spectra horizontal vertical

Modal Damping D 0.05 0.05

Rigid Acceleration SA 1 1

Constant Acceleration SB 2.35 2.33

Minimum Acceleration SMIN 0.1 0.05

Time Value TB 0.08 0.05

Time Value TC 0.2 0.15

Time Value TD 4 4

Cut-Off Time Value TE 0 0

The figure below shows the response spectra for the SEE earthquake as defined in theSeismic Hazard Analysis (SHA) as well as the corresponding EC design spectrum usedfor the calculation.

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Figure 3-18: SEE Design Spectra compared with response spectra defined in SHA

The dynamic interaction between the water body in the reservoir and the Spillwaystructure is modelled by additional masses inserted in the structural model. Theadditional masses are calculated according to the Westergaard approach. The location ofadditional masses is indicated in the picture below as an example for the left Spillwaymodel.

Figure 3-19: Masses considered for the earthquake design analysis

3.10.5 ResultsThe dimensions of the main structural members are adequate. For the detailed results ofthe structural analysis of the Spillway structure please refer to the design report inAnnex 3.2.

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4 NAVIGATION LOCK

4.1 GeneralThe Luang Prabang Navigation Lock (NL) is located at the right abutment. It comprisestwo lock chambers with three mitre gates of which the middle mitre gate is the waterretaining gate when the lock is not in operation. The Navigation Lock can be dividedinto an upper lock from the reservoir till the middle mitre gate and a lower lock with thedownstream mitre gate. According to the MRC Guidance the Navigation Lock has to beoperated between a 30 years flood (Q=21’700 m3/s) and 95% flow duration of the riverin natural conditions (Q=1’100 m3/s).The maximum upstream water level is at elevation 312.50 m asl, equal to Design FullSupply Level (FSLD), and the minimum downstream water level (for navigation) is276.50 m asl. During impounding the Navigation Lock needs to be operational evenwhen the FSL is not reached; the minimum upstream water level for the operation of theNavigation Lock is 294.25 m asl (Lowest Operating Level, LOL).

The filling of the chambers of the Navigation Lock is done via a gravity based feedingsystem from the headwater of the plant controlled by bonneted gates. The lockage timefor a two-step ship lock is expected to be shorter than the required 50 minutes.Due to its location along the right abutment, the Navigation Lock is also a backfillretaining structure for the platforms on the right abutment where also the upstream fishmigration upper channel with the intake / outlet structure is located.

Figure 4-1: Layout of the Navigation Lock

4.2 Structure LayoutThe Navigation Lock is a reinforced Conventional Vibrated Concrete (CVC) U-shapestructure founded on solid rock. All forces from the backfill at the right abutment andthe hydrostatic and hydro-dynamic forces are transmitted in the cantilevered walls of theU-shaped structure into the foundation.The upper lock consists of various independent blocks, divided by contraction joints.The block where the middle mitre gate is located is structurally connected to theSpillway (see chapter 3.2).

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Table 4-1: Upper lock blocks

Block number Width xlengthfoundation

Foundation

Block 2 (u/s mitre gate) 35m x 70.8m Volcanic basalticandesite

Block 3 35m x 77.4m Volcanic basalticandesite

Block 4 (middle mitre gate) 35m x 80.8m Volcanic basalticandesite

Main elevations

Foundation 280.25 m asl

Bottom of lock 289.25 m asl

Top of lock 317.0 m asl

Lock height (concrete) 36.75 m

Width (wall / lock / wall) 12.0m / 12.0m / 11.0m

4.3 Performance CriteriaThe Navigation Lock with the middle mitre gate is a safety relevant structure and mustresist the SEE earthquake without uncontrolled release of water.

The upper lock structure is only partially safety relevant because it is not a waterretaining structure. But due to its proximity to the Spillway approach, the upper lockshall not fail in a way that it obstructs the safe lowering of the reservoir after a SEEearthquake. For this reason, the upper lock will be designed as well for the SEEearthquake, permitting larger permanent sliding displacements and the maximumdemand capacity ratio (DCR).

4.4 FoundationThe resistance against sliding is determined for the LEPTS load cases considering thefriction angle and the cohesion, whereas for the USACE the cohesion has beenneglected, except for the SEE load case.Table 4-2: Shear strength parameters for sliding stability (Navigation Lock)

Navigation Lock

Rock type in contact zone

c [MPa] φs [°]1 φd [°]2



4.5 MaterialThe Navigation Lock consists of C25 Conventional Vibrated Concrete (CVC) withfc’=25 MPa. Other concrete classes are not considered for the basic design stabilityanalysis and reinforcement verification.

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4.6 Design LoadsThe following loads have been considered for the structural design of the NavigationLock:

· Dead Loads of the Concrete Structure


· Uplift

· Lateral Earth Pressure

· Earthquake Loads

4.6.1 Dead LoadThe weight of the concrete is considered as indicated below for the stability analysis.For the structural verification, the weight is considered in the FE model.Water dead loads within the limits of the structural wedge depend on the load case(water level) and are not listed herein but considered in the calculations.Table 4-3: Dead load


Concrete area 867 m2



Equipment load (mitre gate, stoplog, etc.) Not considered

4.6.2 Live LoadNot considered for the stability analysis.For the structural verification according to the Design Criteria report.

4.6.3 Water LevelsThe following upstream water levels have been considered.Table 4-4: Design elevations for the reservoir water levels


Design Full Supply Level (FSL) 312.00 m a.s.l. Normal

Rapid reservoir drawdown 297.00 m a.s.l.


The water level inside the Navigation Lock can either be at the FSL or at the minimumoperating level for the navigation in the reservoir which is at elevation 294.25 m asl.

As indicated in chapter 4.9.2, the water level in the backfill depends on the tailracewater level. The tailrace water levels which have been considered for the stabilityanalysis are:

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Table 4-5: Tailrace water levels


Minimum Operating Level (MOL, Q=745 m3/s) Not relevant

Median Annual Discharge (Q=2’100 m3/s) Not relevant


4.6.4 Backfill LoadsBackfill loads are considered with K0 at rest soil pressure from the first berm onelevation 289.25 m asl till the top of the platform on elevation 317.0 m asl.

Figure 4-2: Backfill at the Navigation Lock

4.6.5 Seismic LoadThe following seismic loads have been considered:Table 4-6: Seismic loads


Horizontal Vertical




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Figure 4-3: LC A1.1 – Normal + low lock level

Figure 4-4: LC B1.1 – Maintenance (lock empty)

Figure 4-5: LC B2.1 – Drainage failure + low lock level

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Figure 4-6: LC B4 – Construction

Figure 4-7: LC C1.1 – PMF


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4.8 Design Method

4.8.1 Stability AnalysisThe stability analysis calculation for the Navigation Lock has been carried out usingExcel, resulting in forces and safety factors for static and pseudo-static loadcombinations.Because the structure fulfils the stability requirements, no further calculations weredone.

4.8.2 Structural VerificationFor the structural verification, a FE-model has been used. The governing SEE load casehas been calculated with a time-history analysis.


4.9.1 GeometryThe Navigation Lock block where the middle mitre gate is located is structurallyconnected to the Spillway. The loads acting in flow direction, including all loads duringan SEE earthquake are not critical due to relatively narrow width of the lock (12 m)compared to the width of the structure (35 m).

Perpendicular to the flow, the upper lock has a similar shape from block with the uppermitre gate till block 4 with the middle mitre gate. Section D-D from block 3 isconsidered representative to prove the stability of the entire upper lock. Compared withother sections, the concrete mass is slightly reduced in the upper part of both walls. Forthe analysis, a width of 1.0 m has been considered.

Figure 4-9: Analysis section of the upper lock chamber

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4.9.2 Calculation of Uplift PressureThere is no drainage gallery and no drainage holes foreseen along the Navigation Lock.Therefore no abrupt uplift pressure reduction has been assumed. The uplift is consideredlinear between the water level in the reservoir and the assumed water level in thebackfill (see chapter 4.9.3).

4.9.3 Backfill Water LevelThe upper lock is founded on elevation 280.25 m asl and the first berm in theNavigation Lock excavation is assumed on elevation 289.25 m asl. It is assumed that theconcrete is poured directly against rock up to the first berm. On top of this first berm, alayer of free draining material that connects to the tailrace area is foreseen. As a result,the water level within the backfill is significantly lower than the reservoir water level.Following assumptions were made:

· Elevation of first berm plus 13.0 m = 302.25

· Tailwater level plus 5.0 m

4.9.4 Results of the Stability AnalysisThe civil structures shall be designed to be safe against sliding, floatation, overturningand foundation bearing. The results of stability analysis are presented below:Table 4-7: Results of the Stability Analysis for the Navigation Lock

4.9.5 ConclusionThe sliding safety factor, floatation safety factor, overturning in term of percent of baseon compression and location of resultant, are quite high and greater than requirement for

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all load cases. The maximum base pressure is well below the allowable pressure for allload cases.

All the stability requirements are fulfilled.

4.10 Structural Verification of the Navigation Lock Structure

4.10.1 Structural ModelFor the finite element (FE) model, the same section as described in chapter 4.9.1, alsowith a width of 1.0 m has been taken into account. Calculations were done either staticor as a time-history analysis for the SEE load case. For the time-history analysis, noresponse modification factor (R-factors) and for the SEE load case, no importancefactors Ic are applied.

As outlined in the Design Criteria, the modulus of subgrade at both borders of thestructure is twice the modulus of subgrade in the rest of the model.

The three sets of time history accelerograms from the seismic hazard assessment areused in the dynamic calculations. For each set of time histories either 360° orientationor

basic design report · 11/11/2019 · b1.1: drainage failure + low tailwater. upstream water level...

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