Probabilistic safety assessment of sea dikes in giao thuy nam dinh

Probabilistic safety assessment of sea dikes in Giao Thuy-Nam Dinh Probabilistic safety assessment of sea dikes in Giao Thuy-Nam Dinh Acknowledgments First of all I would like to send our sincere thanks to: Assoc.Prof.Mai Van Cong and Prof Radu Sarghiuta - my supervisor from ULG and TLU - for their concern, guidance, enthusiasm, valuable advice and assistance with so much warmth and care My high appreciation goes to all the teachers who have taught and armed me with such a valuable knowledge to my future career in my country, my colleagues, friends and my classmates for their support, assistance and for making my stay here filled with joys and memories Pham Tien Hung ULG-TLU-2016 REASSURANCES SOCIALIST REPUBLIC OF VIETNAM INDEPENDENCE - FREEDOM - HAPPINESS REASSURANCES Dear: The management board of Thuy Loi University; The management board of Liege University; My name: PHAM TIEN HUNG Major: Sustainable Hydraulic structure Student Number: 148ULG07 I hereby declare that i am the person who conducted this master thesis under the guidance of Assoc.Prof Mai Van Cong and Prof.Radu Sarghiuta with the research topic “Probabilistic safety assessment of sea dikes in Giao Thuy-Nam Dinh” This is a new research topic which does not overlap with any dissertation before, so there is no copy of any public dissertation The contents of the thesis are presented in accordance with regulations, the data resources and materials used in research are quoted sources If there is any problem with the contents of this thesis, I would like to take full responsibility as prescribed Hanoi, August 15, 2016 Applicant PHAM TIEN HUNG TABLE OF CONTENT TABLE OF CONTENT Contents Acknowledgments REASSURANCES TABLE OF CONTENT CHAPTER1: INTRODUCTION 1.1 Background and justification 1.2 Aim of study 1.3 Study approach 1.4 Outline of study CHAPTER 2: GENERAL OVERVIEW OF STUDY AREA 2.1 Current status of sea dike system in Giao Thuy – Nam Dinh 2.2 Some features of Giao Thuy sea dikes 2.3 General assessment of current situation of sea dike system in Giao Thuy district 2.4 Some natural boundary condition in Giao Thuy - Nam Dinh 10 a) Delta topography 10 b) Soil characteristics and Geological features 10 c) Sediment transport conditions 11 d) Climate and Meteorology 11 e) Oceanography 12 f) Winds 13 g) Waves 14 CHAPTER 3: Probability risk and reliability assessment 15 3.1 General introduction 15 3.2 General background of probability theory 16 a) Risk analysis 16 b) Reliability analysis 17 3.3 Probabilistic reliability analysis of sea dikes system in Giao Thuy-Nam Dinh 23 a) Wave overtopping 25 b) Mechanisms of instability of armour layers of revetment 27 c) Toe foot instabilities 31 d) Piping 32 e) Sliding of dike slope 34 CHAPTER 4: Applying probabilistic reliability analysis to safety assessment in Giao Thuy – Nam Dinh 36 4.1 Wave overtopping 36 4.2 Instability of armour revetments: 40 TABLE OF CONTENT 4.3 Toe foot instabilities 45 4.4 Piping 48 4.5 Sliding of dike slope 53 4.6 Probability of dike system failure 55 CHAPTER 5: Conclusions and recommendation 60 5.1 Conclusions on safety of the sea dikes in Giao Thuy 60 5.2 Recommendations 61 References 63 Appendix 1: The parameters of Giao Thuy sea dike design according to technical standards in sea dike design (2012) 64 a) Grade of structure 64 b) Design water level 65 c) Deep-water wave 65 d) Design wave nears the toe of the dikes 67 e) Required free board by wave overtopping 70 f) Design revetment thickness (technical standards in sea dike design 2012) 73 Appendix 2: Geotechnical document used in calculating sliding of dike slope 74 Appendix 3: Determining failure probability of sea dike system in Giao Thuy by using OpenFTA software 76 Appendix 4: Fragility curve 84 LIST OF FIGURES Figure 1: Map of sea dike system in Giao Thuy-Nam Dinh Figure 2: Erosion in dike slope of Giao Thuy sea dike Figure 3: The flood caused serious damage on field region in Giao Thuy-Nam Dinh Figure 4:Damage of dike section due to Typhoon (2016) Figure 5: Dike section improved by funding of PAM Figure 6: Sketch of double sea dike system at Giao Thuy district (ceg_mai_2004) Figure 7: Representative cross section of sea dike in Giao Thuy-Nam Dinh (ceg_mai_2004) Figure 8: Main seasonal wind directions in northern Vietnam 13 Figure 1:Frame work of risk analysis (see CUR 141, 1990) 16 Figure 2:Definition of a failure boundary Z=0 17 Figure 3:Definition of probability of failure and reliability index 22 Figure 4: Fault tree of Giao Thuy sea dike 25 Figure 5: Damage of sea dike caused by wave overtopping 26 Figure 6: Pore pressure in the subsoil during wave run-down (Pilarczyk et al, 1998) 28 Figure 7: Schematization of scour mechanism at Namdinh revetment 31 Figure 8: Mechanism of piping at sea dike 32 Figure 1: The normal distribution of MHWL based on BESTFIT software 37 Figure 2: Contribution of parameter to overtopping failure mode in current dike 39 Figure 3: Contribution of parameter to overtopping failure mode in dike according to design standard 2012 40 Figure 4: Contribution of parameter to instability armour of revetment in currently 43 Figure 5: Contribution of parameter to instability armour of revetment according to design standard 2012 44 Figure 6: Contribution of parameter to toe foot instabilities 48 Figure 7:Contribution of parameter to piping failure condition 51 Figure 8:Contribution of parameter to piping failure condition 52 Figure 9: Safety factor of slope stability calculation in Outer slope SFmin=1.501 54 Figure 10: Safety factor of slope stability calculation in Inner slope SFmin=1.335 54 Figure 11: Fault tree analysis of Giao Thuy sea dike system for present situation 56 Figure 12: Fault tree analysis of Giao Thuy sea dike according to Dike Design Standard (2012) 57 Figure 13: Fragility curve as a function of the design wave height (Hs)-Appendix 4, page 93 59 Figure A1 1: The Mean High Water Line in Giao Thuy - Nam Dinh 65 Figure A1 2: Plan of regions used to determine the parameters of deep-water wave 66 Figure A4 1: Fragility curve as a function of the design wave height (Hs) 85 LIST OF TABLES Table 1: Sediment load composition on the shoreline of Giao Thuy 11 Table 1: Stochastic variable for mechanism of wave overtopping 38 Table 2: Failure probability of the dike due to overtopping 38 Table 3: Contribution of parameter to overtopping failure mode 39 Table 4: Stochastic variable for instability armour of revetment 42 Table 5: Failure probability and contribution of parameters to instability armour revetment in currently by using VAP 43 Table 6: Failure probability and contribution of parameters to instability armour revetment in dike according to dike design standard 2012 by using VAP 44 Table 7:Stochastic variable for mode of toe foot instabilities 47 Table 8: Failure probability and contribution of parameters to toe foot instabilities by using VAP 47 Table 9: Stochastic variable for mode of piping 50 Table 10: Failure probability and contribution of parameters to piping failure condition by using VAP 51 Table 11: Failure probability and contribution of parameters to piping failure condition by using VAP 52 Table 12: Failure probability of sliding of dike slope in Outer slope and Inner slope by using VAP 54 Table 13: Overall probability of failure at Giao Thuy sea dikes 56 Table A1 1: Safety standard and grade of sea dike 64 Table A1 2: The parameters of deep-water wave in region Hai Phong-Ninh Binh 67 Table A1 3: The results of wave transportation by using SWAN1D software 69 Table A1 4: Average overtopping rates are allowable according to Technical standards in sea dike design (2012) 70 Table A1 5: The required crest free board according to q=10 (l/s/m) 72 Table A1 6: The crest level of Giao Thuy sea dike according to safety design standard 72 Table A2 1: Test result of physical and mechanical properties of soil layer 74 Table A2 2: Test result of physical and mechanical properties of soil layer 74 Table A2 3: Test result of physical and mechanical properties of soil layer 75 Table A2 4:Test result of physical and mechanical properties of soil layer 75 CHAPTER1: INTRODUCTION CHAPTER1: INTRODUCTION 1.1 Background and justification Vietnam is a typhoon prone country located in the tropical monsoon area of the South East Asia The majority of Viet Nam population lived in the low lying river flood plains, deltas and coastal margins which involves mainly in agricultural and fishery sectors In recent years, evolution of natural disasters and weather in Viet Nam was complications, typhoons from the South China Sea bring torrential rainfall and high winds to the coast and further inland On average four to six typhoons attack the coast annually resulting in heavy damage, loss of life, and destruction of infrastructure facilities and services The reason why the water disasters are so serious is that most of the population lives in areas susceptible to flooding Thus the formation and development of defensive system are always attached to life and production of people from generation through the generation Nam Dinh province in general, Giao Thuy district in particular constitutes part of VietNam’s with a long line of dikes and sea defenses Most of the sea dikes are built over the centuries mostly due to local initiatives and have generally an inadequate design and are poorly constructed Due to the bad state of the dikes a significant part of the yearly funds has to be allocated to repairs and maintenance Although, before flood season in every year, several researches on the safety assessment of the coastal defenses system have already been conducted but these researches ’s weakness were done based only on what already happened of the sea defenses system in the previous years and the experiences on management of the monitors As a result, the risk of the damages is still going on at the high rate and frequently and establishing method for assessing safety of sea dikes based on reliability analysis theory is necessary 1.2 Aim of study Probability safety assessment of sea dikes in Giao Thuy-Nam Dinh The aim of this CHAPTER1: INTRODUCTION study can be outlined as follows: - Establishing method for assessing safety of sea dikes system based on reliability analysis theory - Setting up cases of risk in using reliability analysis of this sea dikes system - Suggesting the criteria to estimate safety according to reliability analysis thesis - Finding fragility curve of Giao Thuy sea dikes - Applying results achieved to assess safety of a case study in Giao Thuy district 1.3 Study approach - Applying reliability analysis thesis - Studying the documents involved designing and optimizing sea dikes based on reliability analysis theory at home and abroad - Inheriting early researches relating to sea dikes 1.4 Outline of study - The general information of the study is given in chapter - In chapter 2, description of overview of Giao Thuy-Nam Dinh and some natural boundary condition - The probability risk and reliability assessment and applying probability reliability analysis to safety assessment in Giao Thuy-Nam Dinh are presented in chapter and chapter There will be investigated all kind of failure modes which may occur and estimated which factors have the greatest impact to the failure of sea dike - Finally, the conclusion and recommendations will be treated in chapter CHAPTER 2: GENERAL OVERVIEW OF STUDY AREA CHAPTER 2: GENERAL OVERVIEW OF STUDY AREA 2.1 Current status of sea dike system in Giao Thuy – Nam Dinh Long ago, sea dike system has played vital role in the natural disaster consequences prevention and mitigation Furthermore, in the present recessionary conditions, defense system also has essential role as protection for residential and urban areas to ensure the sustainable economic development Giao Thuy is a coastal district of Nam Dinh province, 35 km South away from Nam Dinh city It is bounded on the Northwest by Xuan Truong district and Southwest by Hai Hau district and also borders Thai Binh on the North and Northeast Giao Thuy district has natural area of 230.22 square kilometers and population of 256,864 people (counted in 2010), surrounded by 27 km of sea dikes from So estuary to Hong estuary Figure 1: Map of sea dike system in Giao Thuy-Nam Dinh 2.2 Some features of Giao Thuy sea dikes In Giao Thuy sea dike, two major problem of defensive system are heavy damages and serious erosion of the coastline That failure due to the current design parameters CHAPTER 2: GENERAL OVERVIEW OF STUDY AREA were not sufficient while the actions of strong storm surges and typhoons are getting stronger The specific features can be listed as following: - The sea dike system in Giao Thuy-Nam Dinh was renovated between 1997 and 2004 with a length of 2580 m at the positions such as: K15.603 ÷ K15.903; K20.350 ÷ K22.267; K 23.685 ÷ K23.935 located majority in Co Vay, Thanh Nien sluice, Ang Giao Phong Due to the innovation in a lot of times, Giao Thuy sea dikes is not ensured In several places, dike sections (K22+400  K27+161) are influenced by erosion which narrowed down the cross-section dike to (1.5-2.0 m) at Giao Phong Giao Lam Figure 2: Erosion in dike slope of Giao Thuy sea dike In which: Bco : Width of berm Lco : Length of berm In this study, Assuming Giao Thuy sea dikes without berm So the value of reduction factor for a berm chosen  b =1 Breaker parameter Given by: 0  tan  2 H s gTm2 Where: tanα=0.25 due to the outer slope of sea dike in Giao Thuy is 1:4 Tm=Tp/1.1 Hs: height of the significant wave After calculation based on the value Hs=1.70, Tp=11.79, we obtained the value of breaker parameter 0 =2.75 Reduction factor for wave angle Assuming the direction of waves to the sea dikes and axis of sea dikes are perpendicular (most dangerous case)        Wave run-up level: This value determined by using (TAW, 2002)  1.6  Ru / H s     f  4.3   when 1,8   bm   10    m   Required crest free board After analysis of parameters, the required crest free board in Giao Thuy-Nam Dinh will be calculated by following formula: 71  Rc  0.2 exp  2.3  H s f   gH s  q    (4.14) due to < γb.ξ m-1,0 < Parameter Design water level Height of wave fronts dike Reduction factor for slope roughness Sign DWL Hs f  Reduction factor for wave angle Average overtopping rate allowable Empirical coefficient Wave run-up level q a Ru Required crest free board Rc Crest level of sea dike Z Mean 2.86 1.7 0.85 Unit m m - 10 0.4 2.02 - 2.9 6.36 l/s/m m m m m Table A1 5: The required crest free board according to q=10 (l/s/m) Design Design Crest free Empirical frequency Crest level water level board coefficient (%) T P Rc a Z (Year) (%) DWL (m) (m) (m) (m) 100 0.90 1.12 0.4 2.42 50 1.19 1.43 0.4 3.02 20 1.52 1.96 0.4 3.88 10 10 1.83 2.75 0.4 4.98 20 2.21 2.86 0.4 5.48 33 2.54 2.96 0.4 5.89 50 2.86 3.10 0.4 6.36 100 3.48 3.70 0.4 7.59 125 0.8 3.60 3.95 0.4 7.95 150 0.67 3.80 4.45 0.4 8.65 200 0.5 4.20 4.58 0.4 9.18 500 0.2 4.40 5.67 0.4 10.47 1000 0.1 4.60 6.82 0.4 11.82 Table A1 6: The crest level of Giao Thuy sea dike according to safety design standard Period 72 f) Design revetment thickness (technical standards in sea dike design 2012) Design wave height Hs 1.7 m System-determined stability upgrading factor u 1.5 - - 2.25 - - Empirical factor-Pilarczyk φ Angle of dike slope α 0.224 rad Breaker parameter ξ0m 2.75 - Relative density of material Δ 1.45 Design revetment thickness (2012) D 73 0.63 m Appendix 2: Geotechnical document used in calculating sliding of dike slope - Layer 1: backfill soil of dike: sandy gray clay, brown clay, yellow gray clay, plastic to stiff with thickness of 1.5 to 2.0 m Physical and No mechanical properties Sign Unit Mean value of soil Wet density w T / m3 1.84 Friction angle   1121' Cohesion C kg / cm2 Permeability K cm / s 6.8 105 Young’s modulus E kg / cm2 120.0 0.159 Table A2 1: Test result of physical and mechanical properties of soil layer - Layer 2: sandy brown gray clay, pink brown clay, plastic to soft with thickness of 2.0-5.0m Physical and No mechanical properties Sign Unit Mean value of soil Wet density w T / m3 Friction angle   Cohesion C kg / cm2 Permeability K cm / s 4.6 105 Young’s modulus E kg / cm2 20.0 1.79 541' 0.105 Table A2 2: Test result of physical and mechanical properties of soil layer 74 - Layer 3: sandy black gray clay, gray clay, plastic to liquefacient, thickness of 5.0 to 6.4m Physical and No mechanical properties Sign Unit Mean value of soil Wet density w T / m3 1.81 Friction angle   827' Cohesion C kg / cm2 Permeability K cm / s 1.5 105 Young’s modulus E kg / cm2 60.0 0.075 Table A2 3: Test result of physical and mechanical properties of soil layer - Layer 4: sandy brown gray clay, brown clay, plastic to soft with thickness of 6.5 to 9.2m Physical and No mechanical properties Sign Unit Mean value of soil Wet density w T / m3 1.75 Friction angle   644' Cohesion C Young’s modulus E kg / cm2 kg / cm2 0.087 60 Table A2 4:Test result of physical and mechanical properties of soil layer - Layer 5: fine gray sand, fine black gray sand, soft with thickness of 9.2 to 15.0m 75 Appendix 3: Determining failure probability of sea dike system in Giao Thuy by using OpenFTA software In case of existing Giao Thuy sea dike: Monte Carlo Simulation ====================== Tree : Current dike.fta Time : Fri Jul 29 16:41:26 2016 Number of primary events = Number of tests Unit Time span used = 1000000 = 1.000000 Number of system failures = 1000000 Probability of at least = 6.628422E-001 ( exact ) one component failure Probability of top event = 6.628422E-001 ( +/- 6.628422E-004 ) 76 Rank Failure mode Failures Estimated Probability Armour 683609 Armour Overtop Overtop Armour Toefoot Toefoot Armour Overtop 4.531249E-001 ( +/- 5.480422E-004 ) 68.36% 162829 121239 1.079299E-001 ( +/- 2.674706E-004 ) 16.28% 8.036232E-002 ( +/- 2.307976E-004 ) 12.12% 14849 10896 Importance 9.842544E-003 ( +/- 8.077161E-005 ) 1.48% 7.222329E-003 ( +/- 6.919006E-005 ) 1.09% 3504 2.322599E-003 ( +/- 3.923667E-005 ) 0.35% 2521 1.671025E-003 ( +/- 3.328102E-005 ) 0.25% Toefoot Overtop Toefoot Armour Innerslope 93 6.164432E-005 ( +/- 6.392219E-006 ) 0.01% Armour Outerslope 89 5.899296E-005 ( +/- 6.253241E-006 ) 0.01% 10 Outerslope 11 Armour condition1 12 Innerslope 60 3.977053E-005 ( +/- 5.134354E-006 ) 0.01% 13 condition1 42 2.783937E-005 ( +/- 4.295708E-006 ) 0.00% 14 Outerslope Overtop 21 1.391969E-005 ( +/- 3.037525E-006 ) 0.00% 15 Armour Innerslope 20 1.325684E-005 ( +/- 2.964320E-006 ) 0.00% 17 1.126832E-005 ( +/- 2.732968E-006 ) 0.00% 79 5.236453E-005 ( +/- 5.891470E-006 ) 0.01% 60 3.977053E-005 ( +/- 5.134354E-006 ) 0.01% Overtop 16 Armour Outerslope Overtop 17 Innerslope Overtop 16 1.060548E-005 ( +/- 2.651369E-006 ) 0.00% 18 Armour Overtop 15 9.942633E-006 ( +/- 2.567177E-006 ) 0.00% Overtop condition1 11 7.291264E-006 ( +/- 2.198399E-006 ) 0.00% condition1 19 77 20 Armour condition2 21 condition2 22 Armour Innerslope 3.977053E-006 ( +/- 1.623625E-006 ) 0.00% 3.314211E-006 ( +/- 1.482160E-006 ) 0.00% 2.651369E-006 ( +/- 1.325684E-006 ) 0.00% 1.988527E-006 ( +/- 1.148076E-006 ) 0.00% Toefoot 23 Armour Outerslope Toefoot 24 Armour Overtop 1.988527E-006 ( +/- 1.148076E-006 ) 0.00% 25 Outerslope Toefoot 1.325684E-006 ( +/- 9.374004E-007 ) 0.00% 26 Armour Outerslope 1.325684E-006 ( +/- 9.374004E-007 ) 0.00% condition2 Overtop Toefoot 27 Armour Toefoot 6.628422E-007 ( +/- 6.628422E-007 ) 0.00% condition1 28 Innerslope 6.628422E-007 ( +/- 6.628422E-007 ) 0.00% Outerslope 29 Toefoot condition1 6.628422E-007 ( +/- 6.628422E-007 ) 0.00% 30 Overtop condition2 6.628422E-007 ( +/- 6.628422E-007 ) 0.00% 31 Armour Overtop 6.628422E-007 ( +/- 6.628422E-007 ) 0.00% Toefoot condition1 Compressed: Rank Failure mode condition2 Failures Estimated Probability Importance 15 9.942633E-006 ( +/- 2.567177E-006 ) 0.00% 78 condition1 131 8.683233E-005 ( +/- 7.586576E-006 ) 0.01% Innerslope 194 1.285914E-004 ( +/- 9.232323E-006 ) 0.02% Outerslope 214 1.418482E-004 ( +/- 9.696545E-006 ) 0.02% Toefoot 31784 2.106778E-002 ( +/- 1.181720E-004 ) 3.18% Overtop 290200 1.923568E-001 ( +/- 3.570745E-004 ) 29.02% Armour 865105 5.734281E-001 ( +/- 6.165163E-004 ) 86.51% Primary Event Analysis: Event Failure contrib Importance Armour 5.734281E-001 86.51% Innerslope 1.285914E-004 0.02% Outerslope 1.418482E-004 0.02% Overtop 1.923568E-001 29.02% Toefoot 2.106778E-002 3.18% condition1 8.683233E-005 condition2 9.942632E-006 0.01% 0.00% 79 In case of sea dike according to dike design standard 2012: Monte Carlo Simulation ====================== Tree : Current dike.fta Time : Fri Jul 29 16:49:40 2016 Number of primary events = Number of tests Unit Time span used = 1000000 = 1.000000 Number of system failures = 1000000 Probability of at least = 1.257806E-001 ( exact ) one component failure Probability of top event = 1.257806E-001 ( +/- 1.257806E-004 ) 80 Rank Failure mode Failures Estimated Probability Importance Armour 681799 8.575708E-002 ( +/- 1.038584E-004 ) 68.18% Toefoot 150298 1.890457E-002 ( +/- 4.876298E-005 ) 15.03% Overtop 133933 1.684617E-002 ( +/- 4.603175E-005 ) 13.39% Armour Toefoot 14815 1.863440E-003 ( +/- 1.530962E-005 ) 1.48% Armour Overtop 13178 1.657537E-003 ( +/- 1.443904E-005 ) 1.32% Overtop Toefoot 2840 Outerslope 968 1.217556E-004 ( +/- 3.913374E-006 ) 0.10% Innerslope 835 1.050268E-004 ( +/- 3.634602E-006 ) 0.08% condition1 602 7.571992E-005 ( +/- 3.086113E-006 ) 0.06% 10 Armour Overtop 3.572169E-004 ( +/- 6.703056E-006 ) 0.28% 274 3.446388E-005 ( +/- 2.082039E-006 ) 0.03% Toefoot 11 Armour Innerslope 95 1.194916E-005 ( +/- 1.225958E-006 ) 0.01% 12 Armour Outerslope 83 1.043979E-005 ( +/- 1.145916E-006 ) 0.01% 13 condition2 14 Armour condition1 15 Innerslope Toefoot 26 3.270295E-006 ( +/- 6.413577E-007 ) 0.00% 16 Outerslope Toefoot 24 3.018734E-006 ( +/- 6.161966E-007 ) 0.00% 17 Innerslope Overtop 23 2.892954E-006 ( +/- 6.032225E-007 ) 0.00% 18 Outerslope Overtop 22 2.767173E-006 ( +/- 5.899633E-007 ) 0.00% 19 Overtop condition1 18 2.264051E-006 ( +/- 5.336419E-007 ) 0.00% 20 Toefoot condition1 11 1.383587E-006 ( +/- 4.171670E-007 ) 0.00% 21 Armour condition2 10 1.257806E-006 ( +/- 3.977532E-007 ) 0.00% 22 Armour Outerslope 6.289030E-007 ( +/- 2.812540E-007 ) 0.00% 73 9.181983E-006 ( +/- 1.074670E-006 ) 0.01% 52 6.540591E-006 ( +/- 9.070168E-007 ) 0.01% Toefoot 23 Toefoot condition2 5.031224E-007 ( +/- 2.515612E-007 ) 0.00% 24 Armour Overtop 3.773418E-007 ( +/- 2.178584E-007 ) 0.00% condition1 81 25 Armour Outerslope 2.515612E-007 ( +/- 1.778806E-007 ) 0.00% 2.515612E-007 ( +/- 1.778806E-007 ) 0.00% 1.257806E-007 ( +/- 1.257806E-007 ) 0.00% Overtop 26 Armour Innerslope Overtop 27 Armour Innerslope Overtop Toefoot 28 Armour Toefoot 1.257806E-007 ( +/- 1.257806E-007 ) 0.00% Innerslope Overtop 1.257806E-007 ( +/- 1.257806E-007 ) 0.00% condition1 29 Toefoot 30 Outerslope Overtop 1.257806E-007 ( +/- 1.257806E-007 ) 0.00% Toefoot 31 Armour Innerslope 1.257806E-007 ( +/- 1.257806E-007 ) 0.00% Toefoot Compressed: Rank Failure mode Failures Estimated Probability Importance condition2 87 1.094291E-005 ( +/- 1.173203E-006 ) 0.01% condition1 687 8.641127E-005 ( +/- 3.296796E-006 ) 0.07% Innerslope 984 1.237681E-004 ( +/- 3.945583E-006 ) 0.10% Outerslope 1105 1.389876E-004 ( +/- 4.181141E-006 ) 0.11% Overtop 150298 1.890457E-002 ( +/- 4.876298E-005 ) 15.03% Toefoot 168302 2.116913E-002 ( +/- 5.160102E-005 ) 16.83% Armour 710321 8.934460E-002 ( +/- 1.060086E-004 ) 71.03% 82 Primary Event Analysis: Event Failure contrib Importance Armour 8.934460E-002 71.03% Innerslope 1.237681E-004 0.10% Outerslope 1.389876E-004 0.11% Overtop 1.890457E-002 15.03% Toefoot 2.116913E-002 16.83% condition1 8.641127E-005 0.07% condition2 1.094291E-005 0.01% 83 Appendix 4: Fragility curve In this study, the fragility curve will be shown the relation between the design wave height (Hs) and the failure probability of dike system in Giao Thuy-Nam Dinh The value of failure probability of each failure mechanism is obtained by changing value of design wave height from 1.1m to 2.6m respectively After that, the failure probability of dike system will be calculated by using OpenFTA software and the result of failure probability in each mechanism and shown below: In case Hs=1.1m, Pf system=2.13e-01 respectively In case Hs=1.2m, Pf system=2.18e-01 respectively In case Hs=1.3m, Pf system=2.31e-01 respectively In case Hs=1.4m, Pf system=2.63e-01 respectively In case Hs=1.5m, Pf system=3.27e-01 respectively In case Hs=1.6m, Pf system=4.30e-01 respectively In case Hs=1.7m, Pf system=5.63e-01 respectively In case Hs=1.8m, Pf system=7.02e-01 respectively In case Hs=1.9m, Pf system=8.22e-01 respectively In case Hs=2.0m, Pf system=9.07e-01 respectively In case Hs=2.1m, Pf system=9.57e-01 respectively In case Hs=2.2m, Pf system=9.90e-01 respectively In case Hs=2.3m, Pf system=9.94e-01 respectively In case Hs=2.4m, Pf system=9.98e-01 respectively 84 In case Hs=2.5m, Pf system=9.99e-01 respectively In case Hs=2.6m, Pf system=9.99e-01 respectively FRAGILITY CURVE 1.20E+00 Probability failure (Pf) 1.00E+00 8.00E-01 6.00E-01 4.00E-01 2.00E-01 0.00E+00 0.5 1.5 2.5 Design wave height (Hs) Figure A4 1: Fragility curve as a function of the design wave height (Hs) 85 ... system in Giao Thuy- Nam Dinh Figure 2: Erosion in dike slope of Giao Thuy sea dike Figure 3: The flood caused serious damage on field region in Giao Thuy- Nam Dinh Figure 4:Damage of. .. safety assessment of sea dikes in Giao Thuy- Nam Dinh The aim of this CHAPTER1: INTRODUCTION study can be outlined as follows: - Establishing method for assessing safety of sea dikes system based... 1: Map of sea dike system in Giao Thuy- Nam Dinh 2.2 Some features of Giao Thuy sea dikes In Giao Thuy sea dike, two major problem of defensive system are heavy damages and serious erosion of the