Probabilistic Design Tools for Vertical Breakwaters

Transcription

1 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

2 TABLE OF CONTENTS PREFACE XV A GUIDE TO THIS BOOK 1 CHAPTER GENERAL BACKGROUND, OPPORTUNITY AND MOTIVATIONS General background and opportunity Motivations and Position of the Design Problem Motivations for Monolithic Coastal Structures / Breakwaters Motivations for Probabilistic Design Methods Position of the Design Problem BRIEF PRESENTATION OF PROVERBS Objectives Research Issues Research Strategy and Development Procedure for Probabilistic Design Tools Overall Strategy Development Procedure for Probabilistic Tools Development Procedure for Partial Safety Factor System (Level I) Representative Example Structures for Application KEY RESULTS AND THEIR PRACTICAL IMPORTANCE Hydrodynamic Aspects (Task 1) Parameter map for wave load classification New formulae to predict impact loading Effect entrained/entrapped air on scaling impact loads Effect of caisson length, wave obliquity and shortcrestedness on impact forces Seaward impact forces induced by wave overtopping Artificial neural network modelling of wave force New prediction formulae for pulsating wave forces on perforated caisson breakwaters New wave load formulae for crown walls 32

3 VI Probabilistic Design Tools for Vertical Breakwaters Development of wave load formulae for High Mound Composite Breakwaters , Geotechnical Aspects (Task 2) Data base for design soil parameters Engineering "dynamic models" Instantaneous pore pressures Degradation and residual pore pressures Limit state equations Uncertainties Influence of design parameters on failure modes Structural Aspects (Task 3) Analysis of existing codes Pre-service failure modes Loads for in-service conditions In-service structural failure modes Hierarchy of refined models Durability of reinforced concrete members Probabilistic Design Tools (Task 4) Toward probabilistic risk analysis and management 55 CHAPTER INTRODUCTION Objectives of Task Technical progress Outline of deterministic design procedure Step 1: Identification of main geometric and wave parameters Step 2: First estimate of wave force / mean pressure over wall height Step 3: Improve calculation of horizontal and up-lift forces Step 4: Revise estimates of caisson size Step 5: Identify loading case using parameter map Step 6: Initial calculation of impact force Step 7: Estimate percentage of breaking waves leading to impacts Pi% Step 8: Estimate impact force using Oumeraci & Kortenhaus' method Step 9: Estimate impact rise time and duration Step 10: Estimate uplift forces under impacts 66

4 Contents VII Step 11: Scale corrections Step 12: Pressure distributions WAVES AT THE STRUCTURE Wave conditions at the structure Near-shore wave transformation Depth-limited breaking Use of parameter map Estimation of proportion of impacts HYDRAULIC RESPONSES Wave transmission over caissons Wave overtopping discharges Wave reflections Vertical breakwaters and seawalls Perforated structures PULSATING WAVE LOADS Horizontal and vertical forces / pressures Seaward or negative forces Sainflou's prediction method Probabilistic design approach for negative forces Deterministic design approach for negative forces Effects of 3-d wave attack on pulsating loads Uncertainties and scale corrections Uncertainties Scaling Use of numerical models Pressures on berms WAVE IMPACT LOADS Horizontal and vertical forces / pressures Horizontal force and rise time Vertical pressure distribution Uplift force Uplift pressure distribution Effect of aeration Seaward impact forces Physical Model Tests Numerical Model Tests Initial guidance Effects of 3-d wave attack on impact loadings Horizontal forces Variability of impact forces along the breakwater Effect of caisson length 111

5 VIII Probabilistic Design Tools for Vertical Breakwaters Uncertainties and scale corrections Uncertainties Scale corrections Use of numerical models Pressures on berms Pressure-impulse modelling BROKEN WAVE LOADS Strongly depth-limited waves Wave loads on crown walls Impact pressures Pulsating pressures Uplift pressures Wave loads on caisson on high mounds Critical wave heights Critical wave pressures Pressures and resultant force for non breaking waves Pressures and resultant force for breaking waves Pressures and resultant force for broken waves Uplift forces FIELD MEASUREMENTS AND DATABASE Dieppe Porto Torres LasPalmas Gijon Alderney Field measurement database Definition of database parameters ALTERNATIVE LOW REFLECTION STRUCTURES Perforated vertical walls Introduction Prototype measurements Model tests Methods to predict forces for perforated caissons Other types of caissons Physics of damping Analysis in time domain Statistical analysis 150 CHAPTER INTRODUCTION 157

6 Contents IX 3.2 GUIDELINES FOR MODELLING Geotechnical failure modes Relevant phenomena Framework of analysis SOIL INVESTIGATIONS AND SOIL PARAMETERS Strategy for soil investigations Seismic profiling Interpretation of CPTU tests Borings, soil sampling and sample testing Borings and soil sampling Soil classification from soil samples Specific tests on soil samples Character of soil parameters Relationship between soil investigations and soil parameters Soil types Importance of density, stress level and stress history Permeability Stiffness Virgin loading Unloading/reloading: elastic parameters Strength Non-cohesive soils Cohesive soils DYNAMICS Concept of equivalent stationary load Basic assumptions of mass-spring(-dashpot) model Prediction of natural periods Prediction of dynamic response factor Inertia with plastic deformation INSTANTANEOUS PORE PRESSURES AND UPLIFT FORCES Relevant phenomena Quasi-stationary flow in the rubble foundation Uplift force, downward force and seepage force in rubble foundation Non-stationary flow in rubble foundation Instantaneous pore pressures in sandy or silty subsoil Relevance of drainage distance Drained region Undrained region DEGRADATION AND RESIDUAL PORE PRESSURES 193

7 X Probabilistic Design Tools for Vertical Breakwaters Relevant phenomena in subsoil Sandy subsoils Clayey subsoils LIMIT STATE EQUATIONS AND OTHER CALCULATION METHODS FOR STABILITY AND DEFORMATION Schematisation of loads during wave crest Limit state equations for main failure (sub)modes during wave crest Seaward failure during wave trough More sophisticated methods More sophisticated limit state equations Sliding circle analysis according to Bishop Finite element models Centrifuge model tests Analysis of unacceptable deformation after several load cycles Three-dimensional rupture surfaces UNCERTAINTIES Survey of uncertainties Uncertainties about soil parameters Model uncertainties INFLUENCE OF DESIGN PARAMETERS General Vertical breakwater on thin bedding layer and coarse grained subsoil with pulsating wave loads Input, analysis and output of performed investigation Less relevant load-case/failure-mode combinations Important load-case/failure-mode combinations Effects with other breakwater types Effect of a high rubble foundation The effect of wave impacts The effect of fine grained subsoil POSSIBILITIES FOR DESIGN IMPROVEMENTS Variation of design parameters if rubble foundation is present Increase the mass of the wall Increase or decrease weight eccentricity e c Reduction of wall volume below still water level Enlargement of B c Enlarging the rubble foundation Connecting caissons to each other Soil replacement or soil improvement 217

8 Contents XI Prolongation of seepage path in rubble foundation Caisson foundation directly on sand Skirts to improve foundation capacity in clayey soils 218 CHAPTER INTRODUCTION Background Design sequence GENERIC TYPES OF REINFORCED CONCRETE CAISSONS Planar rectangular multi-celled caissons Perforated rectangular multi-celled caissons Circular-fronted caissons Alternative designs LOADS ACTING ON THE CAISSON GEOMECHANICAL FACTORS RELEVANT TO THE STRUCUTRAL RESPONSE Characteristics of the ballast fill in caisson cells Characteristics of rubble foundation and sub-soil Unevenness of the foundation HYDRAULIC DATA REQUIRED TO DESIGN A REINFORCED CONCRETE CAISSON Pressure distribution on front face Uplift pressure distribution on base slab Over-pressure on top slab and super-structure FAILURE MODES ASSOCIATED WITH PRE-SERVICE AND IN- SERVICE CONDITIONS Pre-service states In-service states THE NEED FOR A NEW INTEGRATED DESIGN CODE Design standards relevant to reinforced concrete caissons Scope of selected codes Comparisons between design codes Suggested features for a possible new unified design code SIMPLIFIED LIMIT STATE EQUATIONS Identification of structural idealisations Simplified beam and slab analogies and associated limit state equations Limit state equations ULS for flexural failure of a reinforced concrete member 245

9 XII Probabilistic Design Tools for Vertical Breakwaters ULS for shear failure of a reinforced concrete member Cracking in a flexural reinforced concrete member Chloride penetration and corrosion in reinforced concrete elements UNCERTAINTIES ATTRIBUTED TO THE LS EQUATIONS: MORE REFINED STRUCTURAL MODELS Simple 3-degree-of-freedom dynamic model Layered shell non-linear FE models Full 3-dimensional continuum FE models Dynamic fluid-soil-structure interaction Modelling the dynamic far-field Quantifying the uncertainties CONSTRUCTION ISSUES 258 CHAPTER INTRODUCTION GENERAL INTRODUCTION OF PROBABILISTIC METHODS Introduction Limit state equations and uncertainties The concept of limit states Uncertainties related to the limit state formulation Reliability analysis on level II and III Introduction Direct integration methods (Level III) Approximating methods (Level II) Fault tree analysis General system analysis by fault tree Calculation of system probability of failure Introduction Direct integration methods for systems Approximating methods for systems Choice of safety level Reliability based design procedures General formulation of reliability based optimal design Cost optimisation Partial Safety Factor System PROBABILISTIC METHODS APPLIED TO VERTICAL BREAKWATERS IN GENERAL 290

10 Contents XIII Fault tree for a vertical breakwater Specific limit states for vertical breakwaters Introduction Loading of the breakwater Serviceability limit states related to performance of the breakwater Foundation limit states Structural limit states CASE STUDIES General Genoa Voltri (Italy) The case Wave forces Failure functions Variable statistics Model uncertainties System failure probability Sensitivity analysis Effect of breaking Conclusions Easchel breakwater Introduction Breakwater geometry and boundary conditions Inshore wave climate Loading of the structure Influence of the breakwater geometry on the probability of caisson instability Comparison of model combinations for pulsating wave forces The influence of impact loading Reliability analysis of geotechnical failure modes for the Mutsu-Ogawara West breakwater Introduction Stochastic models Reliability analysis PERSPECTIVES Durability Impacts Construction Reflection Shear keys 318

11 XIV Probabilistic Design Tools for Vertical Breakwaters CHAPTER HYDRAULIC ASPECTS GEOTECHNICAL ASPECTS STRUCTURAL ASPECTS PROBABILISTIC ASPECTS 327 ANNEX ANNEX ANNEX ANNEX 4 366