Probabilistic Design Tools for Vertical Breakwaters HOCINE OUMERACI, ANDREAS KORTENHAUS Technical University of Braunschweig, Leichtweifi-Institut fur Wasserbau, Braunschweig, Germany WILLIAM ALLSOP HR Wallingford, Wallingford, U.K. MAARTEN DE GROOT Geodelft, Delft, The Netherlands ROGER CROUCH University of Sheffield, Department of Civil and Structural Engineering, Sheffield, U.K. HAN VRIJLING, HESSEL VOORTMAN Delft University of Technology, Hydraulic and Offshore Engineering Section, Delft, The Netherlands Edited by Andreas Kortenhaus and Hessel Voortman A.A. BALKEMA PUBLISHERS / LISSE / ABINGDON / EXTON (PA) / TOKYO
TABLE OF CONTENTS PREFACE XV A GUIDE TO THIS BOOK 1 CHAPTER 1 3 1.1 GENERAL BACKGROUND, OPPORTUNITY AND MOTIVATIONS 3 1.1.1 General background and opportunity 3 1.1.2 Motivations and Position of the Design Problem 5 1.1.2.1 Motivations for Monolithic Coastal Structures / Breakwaters 5 1.1.2.2 Motivations for Probabilistic Design Methods 6 1.1.2.3 Position of the Design Problem 7 1.2 BRIEF PRESENTATION OF PROVERBS 10 1.2.1 Objectives 10 1.2.2 Research Issues 10 1.2.3 Research Strategy and Development Procedure for Probabilistic Design Tools 12 1.2.3.1 Overall Strategy 12 1.2.3.2 Development Procedure for Probabilistic Tools 13 1.2.3.3 Development Procedure for Partial Safety Factor System (Level I) 19 1.2.3.4 Representative Example Structures for Application 19 1.3 KEY RESULTS AND THEIR PRACTICAL IMPORTANCE 21 1.3.1 Hydrodynamic Aspects (Task 1) 21 1.3.1.1 Parameter map for wave load classification 23 1.3.1.2 New formulae to predict impact loading 25 1.3.1.3 Effect entrained/entrapped air on scaling impact loads 27 1.3.1.4 Effect of caisson length, wave obliquity and shortcrestedness on impact forces 27 1.3.1.5 Seaward impact forces induced by wave overtopping 28 1.3.1.6 Artificial neural network modelling of wave force 29 1.3.1.7 New prediction formulae for pulsating wave forces on perforated caisson breakwaters 29 1.3.1.8 New wave load formulae for crown walls 32
VI Probabilistic Design Tools for Vertical Breakwaters 1.3.1.9 Development of wave load formulae for High Mound Composite Breakwaters 33 1.3.2, Geotechnical Aspects (Task 2) 35 1.3.2.1 Data base for design soil parameters 35 1.3.2.2 Engineering "dynamic models" 38 1.3.2.3 Instantaneous pore pressures 40 1.3.2.4 Degradation and residual pore pressures 41 1.3.2.5 Limit state equations 42 1.3.2.6 Uncertainties 42 1.3.2.7 Influence of design parameters on failure modes 42 1.3.3 Structural Aspects (Task 3) 43 1.3.3.1 Analysis of existing codes 44 1.3.3.2 Pre-service failure modes 44 1.3.3.3 Loads for in-service conditions 46 1.3.3.4 In-service structural failure modes 47 1.3.3.5 Hierarchy of refined models 48 1.3.3.6 Durability of reinforced concrete members 48 1.3.4 Probabilistic Design Tools (Task 4) 48 1.3.5 Toward probabilistic risk analysis and management 55 CHAPTER 2 61 2.1 INTRODUCTION 61 2.1.1 Objectives of Task 1 61 2.1.1.1 Technical progress 62 2.1.2 Outline of deterministic design procedure 62 2.1.2.1 Step 1: Identification of main geometric and wave parameters 63 2.1.2.2 Step 2: First estimate of wave force / mean pressure over wall height 64 2.1.2.3 Step 3: Improve calculation of horizontal and up-lift forces 64 2.1.2.4 Step 4: Revise estimates of caisson size 65 2.1.2.5 Step 5: Identify loading case using parameter map 65 2.1.2.6 Step 6: Initial calculation of impact force 65 2.1.2.7 Step 7: Estimate percentage of breaking waves leading to impacts Pi% 66 2.1.2.8 Step 8: Estimate impact force using Oumeraci & Kortenhaus' method 66 2.1.2.9 Step 9: Estimate impact rise time and duration 66 2.1.2.10 Step 10: Estimate uplift forces under impacts 66
Contents VII 2.1.2.11 Step 11: Scale corrections 67. 2.1.2.12 Step 12: Pressure distributions 67 2.2 WAVES AT THE STRUCTURE 67 2.2.1 Wave conditions at the structure 67 2.2.1.1 Near-shore wave transformation 72 2.2.1.2 Depth-limited breaking 73 2.2.2 Use of parameter map 75 2.2.3 Estimation of proportion of impacts 78 2.3 HYDRAULIC RESPONSES 82 2.3.1 Wave transmission over caissons 82 2.3.2 Wave overtopping discharges 84 2.3.3 Wave reflections 84 2.3.3.1 Vertical breakwaters and seawalls 84 2.3.3.2 Perforated structures 84 2.4 PULSATING WAVE LOADS 87 2.4.1 Horizontal and vertical forces / pressures 87 2.4.2 Seaward or negative forces 88 2.4.2.1 Sainflou's prediction method 89 2.4.2.2 Probabilistic design approach for negative forces 90 2.4.2.3 Deterministic design approach for negative forces 91 2.4.3 Effects of 3-d wave attack on pulsating loads 92 2.4.4 Uncertainties and scale corrections 92 2.4.4.1 Uncertainties 92 2.4.4.2 Scaling 93 2.4.5 Use of numerical models 94 2.4.6 Pressures on berms 95 2.5 WAVE IMPACT LOADS 98 2.5.1 Horizontal and vertical forces / pressures 98 2.5.1.1 Horizontal force and rise time 99 2.5.1.2 Vertical pressure distribution 101 2.5.1.3 Uplift force 104 2.5.1.4 Uplift pressure distribution 104 2.5.1.5 Effect of aeration 105 2.5.2 Seaward impact forces 106 2.5.2.1 Physical Model Tests 107 2.5.2.2 Numerical Model Tests 107 2.5.2.3 Initial guidance 108 2.5.3 Effects of 3-d wave attack on impact loadings 110 2.5.3.1 Horizontal forces 110 2.5.3.2 Variability of impact forces along the breakwater 110 2.5.3.3 Effect of caisson length 111
VIII Probabilistic Design Tools for Vertical Breakwaters 2.5.4 Uncertainties and scale corrections 113 2.5.4.1 Uncertainties 113 2.5.4.2 Scale corrections 113 2.5.5 Use of numerical models 115 2.5.6 Pressures on berms 116 2.5.6.1 Pressure-impulse modelling 119 2.6 BROKEN WAVE LOADS 120 2.6.1 Strongly depth-limited waves 120 2.6.2 Wave loads on crown walls 122 2.6.2.1 Impact pressures 123 2.6.2.2 Pulsating pressures 125 2.6.2.3 Uplift pressures 126 2.6.3 Wave loads on caisson on high mounds 127 2.6.3.1 Critical wave heights 128 2.6.3.2 Critical wave pressures 128 2.6.3.3 Pressures and resultant force for non breaking waves 129 2.6.3.4 Pressures and resultant force for breaking waves 130 2.6.3.5 Pressures and resultant force for broken waves 130 2.6.3.6 Uplift forces 130 2.7 FIELD MEASUREMENTS AND DATABASE 131 2.7.1 Dieppe 131 2.7.2 Porto Torres 131 2.7.3 LasPalmas 131 2.7.4 Gijon 131 2.7.5 Alderney 132 2.7.6 Field measurement database 133 2.7.6.1 Definition of database parameters 133 2.8 ALTERNATIVE LOW REFLECTION STRUCTURES 134 2.8.1 Perforated vertical walls 134 2.8.1.1 Introduction 134 2.8.1.2 Prototype measurements 135 2.8.1.3 Model tests 137 2.8.1.4 Methods to predict forces for perforated caissons 139 2.8.2 Other types of caissons 147 2.8.2.1 Physics of damping 148 2.8.2.2 Analysis in time domain 148 2.8.2.3 Statistical analysis 150 CHAPTER 3 157 3.1 INTRODUCTION 157
Contents IX 3.2 GUIDELINES FOR MODELLING 158 3.2.1 Geotechnical failure modes 158 3.2.2 Relevant phenomena 161 3.2.3 Framework of analysis 162 3.3 SOIL INVESTIGATIONS AND SOIL PARAMETERS 163 3.3.1 Strategy for soil investigations 163 3.3.2 Seismic profiling 164 3.3.3 Interpretation of CPTU tests 164 3.3.4 Borings, soil sampling and sample testing 167 3.3.4.1 Borings and soil sampling 167 3.3.4.2 Soil classification from soil samples 167 3.3.4.3 Specific tests on soil samples 167 3.3.5 Character of soil parameters 168 3.3.5.1 Relationship between soil investigations and soil parameters 168 3.3.5.2 Soil types 168 3.3.5.3 Importance of density, stress level and stress history 168 3.3.6 Permeability 169 3.3.7 Stiffness 170 3.3.7.1 Virgin loading 170 3.3.7.2 Unloading/reloading: elastic parameters 170 3.3.8 Strength 171 3.3.8.1 Non-cohesive soils 171 3.3.8.2 Cohesive soils 172 3.4 DYNAMICS 173 3.4.1 Concept of equivalent stationary load 173 3.4.2 Basic assumptions of mass-spring(-dashpot) model 175 3.4.3 Prediction of natural periods 178 3.4.4 Prediction of dynamic response factor 181 3.4.5 Inertia with plastic deformation 183 3.5 INSTANTANEOUS PORE PRESSURES AND UPLIFT FORCES 184 3.5.1 Relevant phenomena 184 3.5.2 Quasi-stationary flow in the rubble foundation 185 3.5.3 Uplift force, downward force and seepage force in rubble foundation 187 3.5.4 Non-stationary flow in rubble foundation 188 3.5.5 Instantaneous pore pressures in sandy or silty subsoil 190 3.5.5.1 Relevance of drainage distance 190 3.5.5.2 Drained region 190 3.5.5.3 Undrained region 191 3.6 DEGRADATION AND RESIDUAL PORE PRESSURES 193
X Probabilistic Design Tools for Vertical Breakwaters 3.6.1 Relevant phenomena in subsoil 193 3.6.2 Sandy subsoils 194 3.6.3 Clayey subsoils 195 3.7 LIMIT STATE EQUATIONS AND OTHER CALCULATION METHODS FOR STABILITY AND DEFORMATION 196 3.7.1 Schematisation of loads during wave crest 196 3.7.2 Limit state equations for main failure (sub)modes during wave crest 199 3.7.3 Seaward failure during wave trough 201 3.7.4 More sophisticated methods 201 3.7.4.1 More sophisticated limit state equations 201 3.7.4.2 Sliding circle analysis according to Bishop 201 3.7.4.3 Finite element models 202 3.7.4.4 Centrifuge model tests 202 3.7.4.5 Analysis of unacceptable deformation after several load cycles 202 3.7.5 Three-dimensional rupture surfaces 203 3.8 UNCERTAINTIES 204 3.8.1 Survey of uncertainties 204 3.8.2 Uncertainties about soil parameters 206 3.8.3 Model uncertainties 207 3.9 INFLUENCE OF DESIGN PARAMETERS 209 3.9.1 General 209 3.9.2 Vertical breakwater on thin bedding layer and coarse grained subsoil with pulsating wave loads 209 3.9.2.1 Input, analysis and output of performed investigation 209 3.9.2.2 Less relevant load-case/failure-mode combinations 210 3.9.2.3 Important load-case/failure-mode combinations 212 3.9.3 Effects with other breakwater types 215 3.9.3.1 Effect of a high rubble foundation 215 3.9.3.2 The effect of wave impacts 215 3.9.3.3 The effect of fine grained subsoil 215 3.10 POSSIBILITIES FOR DESIGN IMPROVEMENTS 215 3.10.1 Variation of design parameters if rubble foundation is present 215 3.10.1.1 Increase the mass of the wall 215 3.10.1.2 Increase or decrease weight eccentricity e c 216 3.10.1.3 Reduction of wall volume below still water level 216 3.10.1.4 Enlargement of B c 216 3.10.1.5 Enlarging the rubble foundation 216 3.10.1.6 Connecting caissons to each other 217 3.10.1.7 Soil replacement or soil improvement 217
Contents XI 3.10.1.8 Prolongation of seepage path in rubble foundation 217 3.10.2 Caisson foundation directly on sand 218 3.10.3 Skirts to improve foundation capacity in clayey soils 218 CHAPTER 4 225 4.1 INTRODUCTION 225 4.1.1 Background 225 4.1.2 Design sequence 226 4.2 GENERIC TYPES OF REINFORCED CONCRETE CAISSONS 227 4.2.1 Planar rectangular multi-celled caissons 227 4.2.2 Perforated rectangular multi-celled caissons 228 4.2.3 Circular-fronted caissons 228 4.2.4 Alternative designs 229 4.3 LOADS ACTING ON THE CAISSON 229 4.4 GEOMECHANICAL FACTORS RELEVANT TO THE STRUCUTRAL RESPONSE 229 4.4.1 Characteristics of the ballast fill in caisson cells 230 4.4.2 Characteristics of rubble foundation and sub-soil 230 4.4.3 Unevenness of the foundation 231 4.5 HYDRAULIC DATA REQUIRED TO DESIGN A REINFORCED CONCRETE CAISSON 231 4.5.1 Pressure distribution on front face 231 4.5.2 Uplift pressure distribution on base slab 232 4.5.3 Over-pressure on top slab and super-structure 232 4.6 FAILURE MODES ASSOCIATED WITH PRE-SERVICE AND IN- SERVICE CONDITIONS 233 4.6.1 Pre-service states 233 4.6.2 In-service states 234 4.7 THE NEED FOR A NEW INTEGRATED DESIGN CODE 236 4.7.1 Design standards relevant to reinforced concrete caissons 236 4.7.2 Scope of selected codes 237 4.7.3 Comparisons between design codes 237 4.7.4 Suggested features for a possible new unified design code 239 4.8 SIMPLIFIED LIMIT STATE EQUATIONS 241 4.8.1 Identification of structural idealisations 241 4.8.1.1 Simplified beam and slab analogies and associated limit state equations 242 4.8.2 Limit state equations 245 4.8.2.1 ULS for flexural failure of a reinforced concrete member 245
XII Probabilistic Design Tools for Vertical Breakwaters 4.8.2.2 ULS for shear failure of a reinforced concrete member 247 4.8.2.3 Cracking in a flexural reinforced concrete member 247 4.8.2.4 Chloride penetration and corrosion in reinforced concrete elements 247 4.9 UNCERTAINTIES ATTRIBUTED TO THE LS EQUATIONS: MORE REFINED STRUCTURAL MODELS 248 4.9.1 Simple 3-degree-of-freedom dynamic model 248 4.9.2 Layered shell non-linear FE models 251 4.9.3 Full 3-dimensional continuum FE models 253 4.9.3.1 Dynamic fluid-soil-structure interaction 256 4.9.3.2 Modelling the dynamic far-field 257 4.9.3.3 Quantifying the uncertainties 257 4.10 CONSTRUCTION ISSUES 258 CHAPTER 5 261 5.1 INTRODUCTION 261 5.2 GENERAL INTRODUCTION OF PROBABILISTIC METHODS 262 5.2.1 Introduction 262 5.2.2 Limit state equations and uncertainties 262 5.2.2.1 The concept of limit states 262 5.2.2.2 Uncertainties related to the limit state formulation 264 5.2.3 Reliability analysis on level II and III 265 5.2.3.1 Introduction 265 5.2.3.2 Direct integration methods (Level III) 266 5.2.3.3 Approximating methods (Level II) 268 5.2.4 Fault tree analysis 271 5.2.4.1 General system analysis by fault tree 271 5.2.5 Calculation of system probability of failure 272 5.2.5.1 Introduction 272 5.2.5.2 Direct integration methods for systems 273 5.2.5.3 Approximating methods for systems 274 5.2.6 Choice of safety level 275 5.2.7 Reliability based design procedures 277 5.2.7.1 General formulation of reliability based optimal design 277 5.2.7.2 Cost optimisation 279 5.2.7.3 Partial Safety Factor System 284 5.3 PROBABILISTIC METHODS APPLIED TO VERTICAL BREAKWATERS IN GENERAL 290
Contents XIII 5.3.1 Fault tree for a vertical breakwater 290 5.3.2 Specific limit states for vertical breakwaters 290 5.3.2.1 Introduction 290 5.3.2.2 Loading of the breakwater 292 5.3.2.3 Serviceability limit states related to performance of the breakwater 292 5.3.2.4 Foundation limit states 293 5.3.2.5 Structural limit states 293 5.4 CASE STUDIES 294 5.4.1 General 294 5.4.2 Genoa Voltri (Italy) 294 5.4.2.1 The case 294 5.4.2.2 Wave forces 295 5.4.2.3 Failure functions 296 5.4.2.4 Variable statistics 297 5.4.2.5 Model uncertainties 299 5.4.2.6 System failure probability 301 5.4.2.7 Sensitivity analysis 302 5.4.2.8 Effect of breaking 303 5.4.2.9 Conclusions 303 5.4.3 Easchel breakwater 303 5.4.3.1 Introduction 303 5.4.3.2 Breakwater geometry and boundary conditions 304 5.4.3.3 Inshore wave climate 306 5.4.3.4 Loading of the structure 306 5.4.3.5 Influence of the breakwater geometry on the probability of caisson instability 307 5.4.3.6 Comparison of model combinations for pulsating wave forces 309 5.4.3.7 The influence of impact loading 310 5.4.4 Reliability analysis of geotechnical failure modes for the Mutsu-Ogawara West breakwater 311 5.4.4.1 Introduction 311 5.4.4.2 Stochastic models 312 5.4.4.3 Reliability analysis 315 5.5 PERSPECTIVES 317 5.5.1 Durability 317 5.5.2 Impacts 317 5.5.3 Construction 317 5.5.4 Reflection 318 5.5.5 Shear keys 318
XIV Probabilistic Design Tools for Vertical Breakwaters CHAPTER 6 321 6.1 HYDRAULIC ASPECTS 321 6.2 GEOTECHNICAL ASPECTS 323 6.3 STRUCTURAL ASPECTS 325 6.4 PROBABILISTIC ASPECTS 327 ANNEX 1 331 ANNEX 2 357 ANNEX 3 363 ANNEX 4 366