Luận văn thạc sĩ Xây dựng công trình thủy: Probabilistic reliability analysis of Red river dike system protecting Giao Thuy - Nam Dinh

Figure 3-4: Diagram of failure analysis of serial system and parallel system Figure 3-5: Diagram of flood defense system of Huu Hong river dike ~ Giao Thuy district, Dinh province Figure

Master Thesis

Reassurances

Name: Pham Viet Dinh

Major: Sustainable Hydraulic Structures

Student ID # 148ULG010

This is my thesis with the topic "Probabilistic reliability analysis of Red river dike system protecting Giao Thuy - Nam Dinh" under the guidance of Assoc Prof Mai Van Cong - Thuyloi University and Prof Radu Sarghiuta - University of Liege.

I hereby declare that this thesis is the scientific study of my own The results and data in the thesis are honest and no one published it in any other research.

Ha Noi, October 2016

Pham Viet Dinh

Dinh Pham Viet — 148ULGO10

AcknowledgmentsAfier a period of research, my master thesis with the topic "Probabilistic reliability

Nam Dinh" has beenanalysis of Red river dike system protecting Giao Thuy

completed with the enthusiastic help of lecturers, friends, colleagues and my family

To obtain results as today, I would like 10 express deep gratitude to the Assoc.Prof Mai Van Cong from Thuyloi University and Prof Radu Sarghiua from University

of Liege those who were enthusiastic to guide and provide knowledge, documentation,

scientific information as well as contribute valuable comments during the implementation

of this thesis

Lalso sincerely thank the help, the assistance in terms of expertise and experience

of the teachers teaching in class, undergraduate and postgraduate training officeclassmate in Thuyloi University and all my family, friends have motivated, inspired,create favorable conditions in all aspects to completing this thesis

In the process of implementation of the thesis, due to the time and limitedknowledge, there are surely unavoidable mistakes, so Ï wish to receive the comments ofteachers, colleagues to help me improve knowledge in terms of learning and researching

Sincere thanks!

HaNoi, October 2016

Pham Viet Dinh

Dinh Pham Vier ~ L48ULGOIO

Table of contents

‘Chapter 1: General introduction

1.1 Reasonable of this study

1.2, General information

1.3, Intemational related research applications

1.4, Present situation of flood risks in Vietnam

1.5, Study objectives

1.6, Study approach

(Chapter 2: Boundary conditions & description of study area

2.1 Description of dike systems in Vietnam,

2.2, Influence factors

2.2.1 The influence of hydrology

‘The influence ofthe tide

2.2.3 The influence of irrigation planning, traffic and construction

4, The influence of the protected area

2.5 The influence of otber factors

2.3.1 Location

2.32, Topographical characteristics

23.3 Hydrology

2.34, Climatic condition

2.4, Present situations of Huu Hong river dikes

2.5, Practical issues in application ofthe standard criteria and norms

2.6, Overview of traditional design methods:

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2.6.2 Shortcoming in traditional design methods

2.7 Overview of probabilistic design method

2.7.1, General background

212 Historical de ‘lopment of probabilistic design method in the world

2.7.3 The approach of the method of probabilisie design

3/22 Reliability analysis of components in system

3.2.3, Mathematical basis of probabilistic design

3.2.4, Reliability analysis of system

3.3 Application of the probabilistic des

river dike

3.3.1 Case study: Safety assessment of existing river dike system in Giao Thuy district

3.3.2 Possible failure mechanisms of the river dike

3.3.3, Fault Tree Analys

3.4, Conclusion chapter 3

in reliability of river dike system ofthe Huu Hong

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‘Chapter 4: Application of probabilistic reliability analysis to assess safety of Huu Hong river dike

system

4.1, Failure mechanisms to consider

4.1.1, Overflowing mechanism

4.1.2 Instability revetment mechanism

4.1.3, Scouring mechanism at dike toe

4.1.4, Piping mechanism

Dinh Pham Vier ~ L48ULGOIO

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4.1.5, Inner slope instability mechanism.

4.1.6, Fault Tree Analysis

4.2, Establishing fragility curve

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List of figures

‘Figure 2-1: Storms, natural disasters affect the coastal areas in Vietnam,

Figure 2.2: Administrative maps of Nam Dinh province

Figure 2-3: Location of Nam Dinh province on the map (from google map)

Figure 2-4: Overall system map dikes in Giao Thuy district -Nam Dinh province

Figure 2-5: Representative cross-section of Huu Hong river dike,

Figure 2-6: Several photos of current situation of Huu Hong dike

Figure 3-1: Framework of risk analysis (CUR 141 ~ 1990)

Figure 3-2: Reliability funetion is shown in the plane RS

Figure 3.3: Definition ofthe probability of failure andthe reliability index

Figure 3-4: Diagram of failure analysis of serial system and parallel system

Figure 3-5: Diagram of flood defense system of Huu Hong river dike ~ Giao Thuy district,

Dinh province

Figure 36: The failure mechanisms can occur in iver dikes (CUR/TAW 1995)

Figure 37: Overflowing scheme

Figure 38: Instability revetment scheme

Figure 3-9: Scouring mechanism at dike oe scheme

Figure 3-10; Ruptuing scheme Figure 3-11: Sand flowing scheme:

Figure 3-12: Slope sliding scheme

Figure 3-13: Fault Tree diagram of flood defenses system ~ Huu Hong dikes

Figure 4-1: Real measured data of dike crest level

Figure 4-2: Distribution of dike crest level based on real measured data by using BESTFIT

software,

Figure 4-3: Real measured data of flood water evel

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Figure 4-4: Distribution of flood water level based on real measured data by using BESTEIT.

software 50

Figure 45: Influence of random variables tothe overflowing mechanism sĩ

Figure 4-6: Influence of random variables to instability revetment mechanism “

Figure 48: Distbution of flood flow by using BESTEIT software 37Figure 4-9: Influence of random variables to scouring mechanism at dike toe sẽFigure 4-10: Real measured data of upstream water level Cy

Figure 4-11: Distribution of upstream water level based on real measured data by using BESTEIT

software o

Figure 4-12: Influence of random variables to the rupturing mechanism, e

Figure 4-13: Influence of random variables to sand flowing mechanism @Figure 4-14: Results of inner sliding stability by using Geostudio 2007 software 64Figure 4-15: Diagram of Fault Tree Analysis for Hu Hong river dike system 66Figure 4-16: Result of failure probability after using OpenFTA software buigure 4-17: Graph ofthe iterative period with the highest wate level at Ba Lat hydrology

station «Figure 4-18; Fragility curve of comeladion between Pf,,.„, and FWL a

Figure 6-1: Iterative period according to highest water level at Hon Dau, Ba Lat hydrology

Figure 6-7: Result of instability revetment mechanism in ease FWL = 3.62m.

Figure 6-8; Result of scouring mechanism at dike toe in case FWL = 3,62m,

FWL

Figure 6-9: Result of rupturing mechanism in cas 62m

Figure 6-10: Result of sand flowing mechanism in ease FWL, 62m

Figure 6-11: Result of inner slope instability mechanism in case FWL

Figure 6 12: Diagram of Fault Tree Analysis in case FWL = 3.62m

Figure 6-13: Result of overflowing mechanism in ease FWL = 2.0m

Figure 6-14: Diagram of Fault Tree Analysis in case FWL = 2.0m,

Dinh Pham Vier ~ L48ULGOIO

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List of tables

‘Table 4-1: List of random variables according to the overflowing mechani n 30

‘Table 4-2: The probability of the failure and the influence coefficient ofthe random variables to

the overflowing mechanism, sĩTable 4-3: List of random variables according to the ability revetment mechanism, s

‘Table 4-4: The probability of the failure and the influence coefficient of the random variables tothe instability revetment mechanism, s

‘Table 4-5: List of random variables according to the scouring mechanism at dike toe 37

‘Table 4-6: The probability of the failure and the influence coefficient of the random variables tothe scouring mechanism at dike toe sẽ

‘Table 47: List of random variables according to the piping mechanism, 6

Table 4-8: The probability ofthe failure and the influence coefficient of the random variables tothe rupturing mechanism, đt

‘Table 4-9: The probability of the failure and the influence coefficient of the random variables to

the sand flowing mechaniem a

‘Table 4-10: The probability of the failure of the inner slope instability mechanism, 64

‘alle 4-11: Results of failure probability of Huu Hong river dike 63

‘Tale 4-12: Tale ofthe trative period with the highest water level at Ba Lat hydrology station

OTable 4-13: Probabilistic calculation with difference value of FWL 0

Chapter 1: General introduction

1.1 Reasonable of this study

Vietnam has about 3260 km of coastline, mainly consists of coastal lowland is protected

by a sea dike system, natural dunes, and mountains, More than 165 km of coastline in the Red

River delta, populated areas where there are significant changes and dynamic impact destroyedWith intense frequently from the sea (storms, changes in sea level, flow, ete.) Therefore, dikes

are important structures which are buil, maintained and protected through generations to preventfood water, sea water and to protect the lives and property of the government and people, to

promote social and economic Social development, linked to national defense, security

sovereignty, and national benefits The process of formation and development ofthe dike systemalways linked to the life and productive activites of the people from generation to generation

Most dikes are now combined as roads in which many dikes pass through tourist areas, urbanareas and residential areas During the development processes, requirements for dike system as

‘well a the direct impacts of human on the dik re growing and increasing in complex evolution

In recent years, natural disasters and climate changes in Vietnam have had more abnormaland complex In particular, storms and floods are two types of natural disasters which frequently

‘occur and cause the most severe consequences, especially in the area of coastal estuariesHowever, most of the system of dikes and storm prevention, flood prevention existing today in

Vietnam is designed and constructed based on the experience accumulated from many

generations and applied safety standards which only suit economic situation - engineeringconditions of the country in some decades ago Before the adverse effects of weather variations

and changes in an abnormal phenomenon of natural disasters đe to climate change, coupled withthe requirement to ensure higher evel of safety of the protected areas to serve the sustainable

development of economic - society, the research and development applications in reliability

theory of optimal design system against storms, floods and on this basis build up the safetyassessment criteria according to reliability theory and construction process safety assessment

system of dikes in estuaries and coastal areas according to theory of reliability in Vietnamcondition atthe present time and the future is necessary

Pham Vier Dink ~ L48ULGOIO

‘economy and national security, Therefore, the requirements forthe protection ofthe population

and cconomy against the destruction of hurricanes, floods, surges are becoming ever moreurgent Besides the consolidation and upgrade the dike system has had, the planning for river

bank protection, coastline and building the new dike system is in place in all three regions of the

In the current issue of global climate change, Vietnam is one of the countries which is

‘most severely affected In addition, the trend of development in Vietnam as well asthe countriesclose to the sea in the world is seaward development, big cities concentrate on coastal, So

development of marine resources, tourism, and wat refore"Vay iransport are very important Tthe system of dikes and bank protection structure have a very important role IL not only is the

task of protecting people and infrastructure, but also has the task of creating the resort location,

‘beautiful natural landscape, creating refuge areas for ships, pot protection when storm coming

In recent years in the world, the risk of disaster in general and flood, in particular, has

significantly increased trend of frequent occurrence and level of influence The events of the

recent flooding disaster with considerable history as New Orleans, USA 2005; The UK andEastern Europe (2007), Bangladesh and South Asia (2007), Pakistan (2008), and most recently

the flooding disaster in the history ofthe capital Bangkok of Thailand (2011) The floods causedhheavy damage to people and property, So minimizing the risk of floods are now particularly

{interested in many countries around the world

1.3, International related research applications

tific & the re

‘Many hallmarks of rch program around the world related to floodprevention, dikes safety, application development of reliability theory in system and structure

safety can be listed as follows:

‘Netherlands: Netherlands was known as a leading country in flood prevention since they

‘continually invested in research and technology related to this field One of their achievements

was a reliability theory It has been pat into the application to design the erucial components ofDeltaplan program in the 70s Reliability theory continued to develop and extend its application

and became a compulsory subject in civil engineering major in the 1985s After that, design

standards following reliability theory were updated in 1990, 1995 and 2000 Then, with thepurpose to update calculation technologies and safety simulation methods in a dike system of

reliability theory to be high reliability and minimum margin of error, VNK project was

implemented from 2001 to 2008 by Strategic Research Institute PNO, Deft Hydraulics and DeftUniversity of Technology This project provides reliability criteria updated in design standards

"Next, VNK2 project (2007-2010) and SBW (2008-2011) were implemented by the same research

‘group in VNK Project These projects focused on improving the accuracy of the models

simulating with random loads and the durability of the flood prevention structure These arecitical inputs of structure's reliability analysis Besides, the effect of the dikes system length in

safety assessment also investigated profoundly, 3D model design following reliability theory also

appeared, In addition, flood risk standards were checked and updated according to not the onlyperson, community and economy view, but also the culture, history, and the environment, ete

Bri in and Europe: Britain and Europe inherited and developed the study of the

Netherlands to apply to their own country's characteristics, “Reliability of Flood Defenses andIntegrated Flood Risk Management” project (FLOODSite) was implemented from 2005-2009 by

38 institutes & major universities from 20 countries in the region The project gave out the

synthetic approach in the safety assessment of flood prevention, flood management, and flood

ligation systems Reliability theory was confirmed and developed as a core model for thesafety assessment of the system and risk analysis of the flood prevention system Safety

assessment models, optimal design systems and simulated models of loss due to flood were

Pham Vier Dink ~ L48ULGOIO

developed and examined by the experimental application in the countries Integrated models,

Solution 1& 2, were developed to apply in EU member countries Member countries came to an

‘agreement to develop and use the same standard safety assessments in dike systems and flood

prevention.

and Canada: These two countries developed the application of the reliability theory

in dams safety, especially high dams in the 90s, Standard system was converted completely fromtraditional safety standard (safety factor) to safety methods following allowable reliability |J]

Recently, atypical application in design standards according to reliability in U.S was a designproject, planning in flood prevention system of New Orleans with system allowable reliability of IBỊ=42

Russia and China: Russia and China applied the reliability theory in quantitativestructure safety following the technical standards using allowable reliability [] The application

‘was mainly applied in dam design China limited the reliability of several specie structures by

fixed reliability value For example, the reliability value of reinforced concrete was 3.6 < p< 4.2Russia used reliability to adjust several coefficients in design such as overloading factor, ete

‘The standards of risk management and flood prevention structure safety assessment areconstructed and applied in Š recent years,

1.4 Present situation of flood risks in Vietnam

‘To evaluate an overview of the work of dikes and issues of safety of flood prevention in

‘Vietnam, we can cite several points stated in the "National Strategy for Prevention and DisasterReduction 2 0" as Follows:

Vietnam is located in the tropical monsoon, one of five storms ofthe Asia - Pacific

region, offen faced with this kind of natural disaster, floods and storms at most

In recent years, natural disasters occurring in all areas of the country have caused loss of

life, property, infrastructure, economic, cultural, social and environmental adverse impacts In therecent 10 years (1997-2006) the disaster killed, missed nearly 7500 people and the damage is

estimated at 1.5% of GDP Due to the impact of global climate change, Vietnam is among

‘countries most affected by sea level rise and other impacts of natural disasters increase in size as

‘well as iterative period and unpredictable,

FFor decades, the investment of government and the effort of people have created theinfrastructure system of prevention and mitigation of natural disasters and relatively uniform

across regions The system of river and sea dikes on the 4500 km, large reservoirs serving the

flood reduction, water regulation, electricity generation was based on the fixation of large riverbasins The ierigation-transportation structures, construction of residential flood prevention,prevent floods and erosion control projects, boats mooring zones to avoid the storm, forecasting

‘warning system, communications, rescue aid victims have progres ely improving

disaster prevention before coming, Red river delta has been coping with flood frequency of 500yeurs, which is the level of regional guarantee, Mekong Delta lives with floods increasingly

proactive, contin agricultural production and harvest stability during the past decade,

Intemational cooperation development is of importance of prevention and mitigation ofdisasters Vietnam has actively participated in and contributed tothe forums and international and

regional commitments (o the prevention and mitigation of disaster risk and climate change

framework action Hyogo, Kyoto Protocol, Asian general agreement about the cooperation dealbefore the disaster The international community has helped Vietnam to train human resources,

transfer of technology, experience, raise awareness, build models Especially ODA projectsintended for flood prevention structure and mitigation of natural disasters; the non-refundable

ODA projects for the local industry have brought very practical effect,

15 Study objectives

The purpose ofthis study can be presented as follows

+ Safety assessment of existing river lod defenses of Giao Thuy

+ Determination ofthe reliability of Huw Hong Dike section for present condition

+ Establishment of the statistical probability distribution of loads (water level, discharge)

‘and strength (soil properties) of the dike section

+ Quantifying the sk due to flooding in the protected area

Pham Vier Dink ~ L48ULGOIO

Expected outcomes:

+ Using analysis methodology and the scientific basis of risk analysis and reliabilitytheory to perform a safety assessment of the river dike system,

+ Safety of Huu Hong river dike sections protecting the Giao Thuy district and

recommendation of how to improve the safety ofthe system

1.6, Study approach

In this research, the following approach will be used in the study

Collect the necessary data from all possible sources, including the subject

Point out the future predictions of the probability of failure mechanisms for Giao Thuy dike

Review of previous related studies that deal with Huu Hong river dike

~ Review the existing ike design in Vietnam,

- Evaluate and determine the safety of the river dike in Giao Thuy by applying reliabilityanalysis

Chapter 2: Boundary conditions & description of study area

21 Deseription of dike systems in Vietnam

Vietnam is a country located in the tropical monsoon climate with abundant and diverse

‘geomorphic, topography; West mountain, Northern-West mountain, and East mountain are

surrounded by the sea and dense river systems Residential areas, cities, and agricultural areasoften develop along the riverside areas and often are influenced by factors and risk of flood Dike

system along the river branches isa solution of flood prevention which was used for a longtimeago to protect residential area along riverside and entire delta region from the tisk of flooding

For a long time of development, the curr

system with about 13,200km of dike, of which about 10,600 km river dike and nearly 2,600kmsea dike, The main river dike system with over 2,500 km of the dike from grade HH to special

dike system in the country is a large-seale structured

srade; remaining dike is under grade IIL and has not been yet decentralized In which:

Dike systems of North and North Central: 5,620km of length, with flood protection is

responsible for flood protection, ensuring safety for the Northern Plains and North Central

~ River dike system, estuarine areas of Central and South Central: a total length of 904km

‘The system of river dikes, embankments in Mekong Delta area: 4,073km of length,

In terms of the socio-economic development of the country at present, the requirementsfor the protection of the population and economy against the destructive of hurricanes, floods,

surges are becoming ever more urgent Besides the consolidation and upgrade the dike system

hha had, the planning for river bank protection, coastline and building the new dike system are set

‘out in all three regions ofthe country

In the current issue of global climate change, Vietnam is one of the counies whieh is

most severely affected In addition, the trend of development in Vietnam as well as the countriesclose to the sea in the world is seaward development, big cities concentrate on coastal So

development of marine resources, tourism, and waterway transport are very important Thereforethe system of dikes and bank protection structure have a very important role, Besides the task of

Pham Vier Dink ~ L48ULGOIO

protecting people and infrastructure, it also has the task of creating the resort location, beautiful

‘natural landscape, creating refuge areas for ships, port protection when having a storm,

2.2, Influence factors

2.2.1 The influence of hydrology

Hydrologic factor influences markedly on the dike crest level for river dike and estuary

dike Component affects to the calculation formula of the dike crest level consist of design flood

‘water level rising water level due to wind and wave

“The design flood water level of the dike is determined to correspond to the guaranteedfrequency of flood prevention design of the dike (to be taken according to the level of the dike by

norm) Flood frequency curve is built from a series of annual measured flood data

‘Water rising due to the wind causes the influence of hydrology by these Factors: wind

<itection; wind velocity, wind momentum; the depth of the water level in front of the dike

“The height of wave run-up depends on many factors such as the parameters of the wave infront of the dike, dike slope coefficient, guaranteed wave mun up levels, roughness and

permeability of slope, wind velocity, depth ofthe water level in front of the dike, the direction of

wave propagation ete, In which, the influence of the hydrologie factors ineluding: wind

direction, wind velocity, the time the wind blows continuously, wind momentum, the parameters

‘of the waves in front the dike, the depth of the water level in front of the dike

2.2.2 The influence of the tide

“The tide affects considerably to the crest level of the dike and estuary dikes Compositionaffects to the calculation formula dike crest level, including calculation sea level, height storm

surge, and height of wave ru

‘Sea water level is calculated from a guarantee frequency in the work place, including theastronomical tide and variable values due wave, flood, earthquake, fake tidal, water changing

level, long-period variable, ete without regard to the storm surge

‘The height of the rising water level is determined by the frequency and latitude In thiscease, real measured data of tide is used to analyze the frequeney If the tide has components

including surges, no need to calculate this quantity anymore

2.2.3 The influence of irrigation planning, traffic and construction

Invigation planning, trafic planning and building planning transform boundary conditions

Of the dike crest level computing, such as conditions of topography, hydrology, hydraulic Inparticular:

~ The construction of the system of reservoir in upstream of the river basin will change the

‘low of water in the river to downstream;

The construction of hydraulic structures, traffic om the river as the dam, bridge across theriver changes the hydraulic regime of rivers;

~ The planning of construction of transport routes at downstream will change the direction

‘of flood drainage, and it also affects the capability of flood drainage to the sea;

“The construction of urban planning, infrastructure of presidential area would reduce the

flooding storage zone and narrow the section of flood di

Pham Vier Dink ~ L48ULGOIO

22 1 The influence of the protected area

In the approach of the traditional method, the scale of protected area affects directly to thelevel of the dike design, Then it affects the guaranteed frequency and allowable safety for the

dike

In the approach of the probabilistic method, the scale of protected area affects the level of

damage when the faire occurs The level of damage of the failure affects the risk because the

risk isa funetion of he failure probability and the consequences The dike crest level is defined4s the optimal balance plan between risk level and investment costs of constructing the system, or

in other words, the dike crest level is determined based on the probability or frequency of

acceptable damage of protected areas Therefore, the scale of protected areas directly impacts thedike exest level

2.2.5 The influence of other factors

In addition to the above factors and other factors also affect the dike crest level, such as

topography, geology, the cross-section shape of the dike, functions and tasks of the dike, ete

‘Topography affects the wind factor, wave in front of the dike;

Geology can affect the shape of cross-sectional structure, from that it affects to the wave

factor of the dike In addition, the foundation of dike also affects to the setlement of the dike;

- Topography and geology also affect the changing of the river bed, river bank, coast,

sediment and main flow;

~ Shape cross-section of dike fects the wave factor in front the dike as the wave run-up;

~ Functions of the dike also affect the dike erest level as wave-breaking, dike allows water

40 spill over or does not allow water to spill over, the position and functions of dike protection

system consisting of two or more dike axis (main dike; coffer dike )

2.3 Natural conditions

2.3.1 Location

(Giao Thuy district is located in the South East of Nam Dinh province, which is in the

[Northern Delta of Vietnam Its coordination is 20°21°N 106°21'-106°35E,

- Giao Thuy district is bordered by Thai Binh province to the North East, Xuan Truong

district tothe North West, Hai Hau district to the West and East Sea to the South

~ Giao Thuy district has good conditions for both waterway and roadway, which makes a

‘good connection to other districts of the province or other provinces The total area of the district

is 238.24 km,

Figure 2-2: Administrative maps of Nam Dinh province

2.32, Topographical characteristics

‘The topography of the study area is quite flat and lower from North to South; it can be

divided into two part inside ground and alluvial ground along the seaside Soil condition of the

istrict facilitates the agricultural development, especially for cultivating With 32km seaside,

‘wide fishing ground, a variety of sea creatures and beautiful beaches, the district also has a good

‘condition for fisheries and tourism,

Pham Vier Dink ~ L48ULGOIO

Giao Thuy has an almost climatic condition of the Red River Delta area that is affected by

‘tropical monsoon climate with four distinct seasons: Spring, Summer, Autumn and Winter

‘Temperature: the annual average temperature is 20°C, the highest is 39°C in June and the

lowest is 5°C in De: and January

‘Sunshine: Annually, there are about 250 sunny days, total sunshine hours are about

1650-1700 hours 3 months of the summer (May, June, July) have the most sunshine hours with the

average of 170 ~ 200 hours per month, November has the least sunshine hours with about 40-45hours per month,

‘Humidity: the humidity ofthe atmosphere is pretty high with an average of 75-80% and a

large amplitude Sometimes the humidity is up to 90%, but sometimes it is lower than 30%

Rainfall: the average rainfall is 1400-1600mm, The rainfall distributes irregular, rainy

season from May to October make about 75% of the total rainfall in a year, especially in July,

and September Because of that distribution, it usually has flood in the rainy season, The

Flood has a bad effect on agriculture and the

‘Wind: the most common wind direction is Southeast but it changes due to the season The

‘common wind direction in winter is North-East then changing into East direction, and the most

common wind direction in summer is a West wind (the wind from Laos) Moreover, this area

ed wind and heavy rain, which makes flood andusually has a tropical storm with high-s

2.4 Present situations of Huu Hong river dikes

"Nam Dinh province is a part ofthe coast of Vietnam witha total length of about 70 km,

which is protected by a system of river dikes and sea dike, The dike system has been severelyeroded and severely damaged to the flood defense system, There were many’ times of dike break

‘hich caused serious flooding and losses The present situation of Nam Dinh dikes can beconsidered a typical coastal area in Northern part of Vietnam In general, the erosion and

damages of coastal defenses occur frequently, sò it results in serious economic consequences as

‘well a the social consequences of the relevant locations,

(Giao Thuy, a coastal distict belong to the Nam Dinh provinee, locates at the edge of the

Red River delta, and far 45 km from Nam Dinh City to the south, Flood defense system of Giao

‘Thuy district, including 31.161 km of sea dike from K0+000 to K31+161 and nearly 30km riverdike in which 11.702 km length of Huw Hong dike segment locates from K208+000 toK219+702 (see figure 2-4) Dike crest level from +4.5m to +5.0m; width of erest surface from

Pham Vier Dink ~ L48ULGOIO

4.5m to Sm which has been renovated and reinforced for many years This dike also is publicroads for 6 communes and Ngo Dong town along the dike.

- For the dike from K208 + 153 to K208 + 735: The current dike crest surface is a

‘concrete road that is still relatively good,

For the dike from K208 + 735 to K210 + 670: The current dike erest surface is concrete

roads which were heavily damaged, does not guarantee the load conditions and necessary toremove and reinforcement

Figure 2-4: Overall system map dikes in Giao Thuy district - Nam Dinh province

Dikes of Giao Thuy district were built a long time ago (about 250 years) on a weakfoundation (sediment accretion of the Red River system) Dikes stretch from the estuary of Red

River in the North (beginning of the line) to So River (Ha Lan estuary) in the South (end of the

line) that has a complex terrain with terrain conditions and geological conditions changefrequently Not only being direetly influenced by tides and winds of the storm from the South

China Sea but also being affected by flood flows into the South China Sea from inland

‘waterways, So the coastline in Giao Thuy became complicated for some years ago Middle of

‘coastline which is faced to the sea was occurred seriously erosion,

` = fe a

† °

Figure 2-5: Representative cross-section of Huu Hong river dike

Filled s il in dike body and the foundation is low quality in many dike segments, which

almost is sand and sandy soil, so itis easy to be slided by rain and wave The important locationwas protected by dike revetment but often being ruined because revetment structure and the toe

‘of revetment were not suitable (revetment was constructed of dry masonry) Some sluice was

built about 40 years ago, and some of the sluiees were shorter than dike body, so the form and

structure were outdated or even has been damaged and degraded Therefore, it does not meet the

requirements of present flood defense,

Although existing dikes were built and upgraded through periods in order to meet the

requirement of flood prevention safety standards at 1/100 years for river dike The fact is that thefuluse still frequently occurs at critical locations along the river dikes

In recent times, along with the global climate change, the damage caused by natural

disasters tends to increase around the world Those slorms have a strong upward trend, and theycan become the destructive heavy typhoon The phenomenon of heavy rain, gust, tomadoes also

‘ocours more frequently In many parts of the world, the phenomenon of earthquakes and tsunamis

also occur frequently and cause more erious consequences immensely

“The socio-economic activities in coastal and seaside cause changing in the natural

environment in the direction of disadvantage and increase the damage of natural disasters Inmany areas, mangroves and coastal forests have been lost that lead to not only cause changing in

the ecological environment in Ways that are harmful, but also make billow hit straight into the seadike, causing sea dike breaking and flooding

Pham Vier Dink ~ L48ULGOIO

Although there have been some reports on the safety assessment of the coastal defense

system before the flood season in each year, but those reports are made based on management

experience and history oecurred in the defense system in the prior year The risk of damage isstill intense and frequent Therefore, the safety assessment of the existing defense system and

analysis of the current situation based on the latest design are necessary

ia and norm:

2.8 Practical issues in application of the standard eri

‘The standard system and norms ike design in our country is old and cannot yet updatethe actual situation of the current situation, The classification of the dike is incomplete for all

regions in Vietnam Dike classification is an important regulation, which affects the design

criteria and scale of structure,

Nowadays, there are no design standards for river dike (new draft river dike design

standards in 1999 that have not be enacted) In particular, the standard 14TCN 130-2002

"Design guidelines for sea dike" only applies to sea dike structure

“The design of the estuary dike sills difficult because there are no specific standards (0

apply Calculating just only follows characteristic that can be applied partly according to the seadike

“The regulations, standards and norms only guide to caleulate waves and surges butfragmented, inadequate and unsystemati; tide combination, storm and flood forthe river dikes in

the some river sections, which are affected by tide, still not regular to be specified for each region

2.6 Overview of traditional design methods:

2.6.1 Background information

‘Current traditional sign of the structure is calculated according to the deterministic

‘method, In this method, the design values of the load and the parameters of strength are

considered to determine, corresponding to each case and design combinations The designerselects limited condition corresponding to its suitable design combination load This limited

corresponds the characterized strength of the structure

Pham Vier Dink ~ L48ULGOIO

‘Structures are considered safe when the distance between load and strength is large

enough to en + satisfying of each limit state ofall components of the structure

Calculating in this way, just only solves two problems which are overall stability andstrength stability of the structure

The content ofthe traditional design method as follows:

4a, Allowable stress method

According to this method, strength conditions ofthe form

Saas $ [6] 4)Where:

+ Om: The largest calculated stress at a point, determining from the most

disadvantaged load combination;

+ [o]: Allowable stresses, obtained according to documents and criteria

eulating according to safety factor method:

‘This method is usually used in the calculation of stability The checking formula is:

€ Calculating according to safety limit states method:

Specific characteristics ofthe calculating according to safety limit states method is using &

‘group of safety factor with statistical characteristics as load combination coefficient ne, working.

conditions coefficient m, reliability coefficients Ky, load deviation coeffi ny the safetyfactor for materials Ky This group of coefficients is replaced by a general safety factor K This

method is classified into 2 calculation groups: first limit state and second limit state,

Ny <mRUK, 23)Where

+ Nụ: Calculated numeric value of summing load;

+R: Calculated numeric value of strength of structure2.6.2 Shortcoming in traditional design methods

“The hydraulic structure is affected by natural factors, which mainly are random factors,

“The hydraulic structure design aeconding to traditional solutions ean not consider the randomly of

impact factors as wel as the factors that make the load of structure, so this method is sil limited

In many cases, the structure was calculated with the largest load, the maximum loaded, greatselection safety fator, but the structure still occurs the incident The case like this based on the

‘theory of traditional design cannot explain

‘Some limitations of traditional design methods can be cited as:

+ The failure probability of each components as well as the whole system canot yet

+ Overall properties of a completed system has not yet mention;

+ In the design, it has not yet mentioned the influence of the scale of system (length ofdikes.)

+ Can not compare the strength of the various sections such as shape and position:

+ Can not give the failure probability and the extent of damage tothe protected area

27 Overview of probabilistic design method

2.7.1 General background

‘The evolution of logic methods in structural design has been summarized as followsInitially, they were calculated according to the deterministic methods (according tothe allowable

stresses and safety factor), the premise isthe load calculation and strength has been the default

during the working process of structure In fact, the load funetion and durability impact of manydifferent factors, and laws change randomly So the previous fixing of the calculated value of

them during the working time is not satisfactory yet On the other hand, to inerease the level of

Pham Vier Dink ~ L48ULGOIO

reserve safety, we must reduce the value of allowable stress, or increase the safety coefficient.

‘This increase and decrease are unavoidable to subjective factors

“The turing to limit state method is a step forward on the path of improving the structuredesign method, Limit state method essentially is quasi-probabilistic, where the partly safety

factor (n., Ky, m, Ky.) is determined according to statistical probability

‘The next move followed the tuming to probabilistic approaches within the framework of

the reliability theory, This theory considers the frequently changing of the load and impact,

material properties, structure self-weight

2.7.2, Historical development of probabilistic design method in the world

“The late 1960s and 70s of the XX century, the world has made the published research onthe application of reliability theory in the field of construction The concept of “probability

ensures no failure” as well as calculating this probability has become familiar in the field of

construction

“The 1970s to 1990s of the XX century appeared series

‘The researeh was focused on building the calculation reliability methods which can be applied to

sarch on structure reliability

technical problems and developing the optimum design according to reliability This problem was

_growing both in the Soviet Union and European countries, even in America

Reliability theory has also been applied to the field of computing the hydraulic structure

since the 90s of the XX century The probabilistic design and the risk design were developed

{quite strongly inthe field of sea and shore protection structure

In Vietnam, the theory credibility has also been infiltrated from the 1960s, sinee then it

has been continuously developed The firs, the theory was disseminated by the books, lectures,teaching curriculum in the university Next is the research within the framework of the master

thesis, doctoral thesis in the transport industry, construction, hydraulic structure, dike, andstructure to protect the river banks On the structure of co struction sector had the originalregulations forthe structural reliability In comparison with the world, this theory application in

2.7.3 The approach of the method of probabilisie design

In the case all causes of possible failure of structure can be listed, and the probability ofpossible failure certainly can be identified, so in principle itis able to determine the probability of

the failure Hence, we can give a new approach in the structure design with the idea "Need to

‘consider extent possible to build structural safety standards based on risk analysis forall relevant

factors" This is the basic reason of the developing method “structure design according to

probabilistic theory and reliability analysis"

‘The probabilistic design method is a design method based on basis of statistical

probability mathematics to analyze the interactions between the random variables of the load and

the resistance in the failure mechanism under the limit state of the structure In a probabilisticdesign, all the failure mechanisms are described by mathematical modeling or simulation models

respectively Calculating the failure probability of a part of structure or the structure is based on

the reliability function of each failure mechanism,

In the theoretical basis application of the method of probabilistic designs, Tam going,

to study and analyze in Chapter 3

28 Conclusion chapter 2

Long time ago, the system of dikes and bank protection structures play an important role

in the flood prevention, disaster mitigation In the present situation, dike system and protection

structures have also added 4 more important role, such as: ensuring the safety of residential areas,

‘urban areas, catering to the task of economic development sustainable soci

develop Cin the whole ofthe society

‘The system standards and norms are old, sporadic and incomplete Design method has

many limitations, some issues have not been mentioned (such as rising sea levels due to global

climate change) The determination of he calculated parameters is lacking scientific basis or not

‘consistent with the actual situation

On the method designed base on deterministic model, the lacking is unavoidable and can

not mention to the possibility of occurring the load exceeds or smaller than the design load The

Pham Vier Dink ~ L48ULGOIO

cause of this lacking comes from choosing a value of specific design load This is a serious

lacking in the estimation ofthe level of failure of the structure

Structural analysis according to probability theory in the framework of reliability theory is

4 logical development, gradually developed from the safety factor method, quasi-probabilisic

method, to analyze the load boundary, the load capacity of the material, strcture characteristics

and working conditions of the structure

“The research of applying probabilistic design method in dikes and flood defense system in

‘general and for the Huu Hong river dike in Giao Thuy district - Nam Dinh province, in particular,isa ight way and suitable with the current trend,

marlllance

Chapter 3: Safety assessment & reliability analysis of Huu Hong

river dike

3.1 Background theory

In recent decades, the design embankments and flood prevention structures have been

developed On previous traditional methods, dikes were designed mainly based on experienceAccordingly, the dike crest level is determined based on the biggest flood level of historical flood

events might be recorded In many parts ofthe world, the design of dikes, sea, and river dikes are

‘based on the concept of water level corresponding to design frequency For the dikes, the water

level is determined based on the statistics and called the design the water level, determined by a

design Frequency or appearance frequency

“The appearance frequency of the design water level was established to widely apply as a

safety standard for areas protected by dikes; it was built based on the probability of flooding

However, this theory is trae only for the ease when the incident of dike occurs due to the floodexceeds the design water level; it i not suitable inthe ease of flood level smaller than the design

water level

Safety standards for cach type of structute ba

ds

ed on the traditional approach to design is

Freques n of load and general safety factor and each component of the structure, for each

‘mechanism failure According to a probabilistic approach and theory of reliability, safety

standard is limited in terms of the probability ofthe incident of the whole system structure and

this damaged of systems are considered random combinations damaged of the components of thesystem according to the possible failure mechanism The probability of failure of the structural

system is related closely to the exceeding frequency of impact load However, the two concepts

re not identical and eannot replace cach other

In principle, we can determine the probability of flooding occurrence in the ease ofall the

causes of dike failure can list and the probability of each failure can certainly be determined

Because this current calculation cannot be done easily in application design, so dikes designingstill determine the design frequency (irequency of exceeding the load of the main parameters)

based on frequency acceptable occurred flooding

Pham Vier Dink ~ L48ULGOIO

Based on the above issues, the probability of occurrence of the load parameters built in

design eriteria and was chosen as the safety assessment criteria flood prevention, In Vietnam, the

frequency the water level designing around 1/20 to 1/100, frequency designing discharge flow(or river dikes) ranges from 1/50 to 1/1000, this value depends on the level of importance ofprotected areas.

According to the idea of the methodology above, we may create a new approaching

‘method in the construction design with the idea: It is necessary to consider the level of standard

structure design based on risk analysis of all related Factors,

‘This is the fundamental reason for the development of "Structure Design according to

probabilistic theory and reliability analysis

3.2 Theoretical basis

3.2.1 Risk analysis

a Risk definition

Risk analysts do not agree on the concept of risk Typically, there are four definitions of

risk analysis are given:

«Definition 1: Risk is the probability of an unwanted failure in a process or an object.

Definition 2: Risk isa consequence of an unwanted failure

Definition 3: Risk is a multiplication of the probability of failure and the consequences

of the failure

- Definition 4: Risk is a function of the probability of occurrence of damage and the

‘consequences of the damage

In general, the frst and second definitions do not suit Because risk includes 2 factor:

failure probability and consequences of the failure

The third definition gives a better comparison of risks However, because the probability

‘of the falure is dimensionless, but the consequences of a failure often are dimensions anddifferent about properties, so the tisk can not be described in just a number

“The fourth risk definition is the most general definition of the four mentioned definitions

> General risk formula

The most general definition of the risks of natural disasters and floods was recognized byinternational scientific organizations and now being widely adopted in many countries as follows:

Risk =( Probability (Consequence)

In oder to minimize the tisk of flooding, many countries have made on the application of

the definition of the combination of two main groups of solutions:

1) Group of solution 1 — Reduce probability of failure

‘We need to reduce the probability of flooding by measuring to improve the safety of the

flood protection system such as increasing stabilized, reinforcing and upgrading of dikes, dams,and systems of flood prevention structure

2) Group of solution 2 - Reduce consequences

‘Minimizing consequences of the damage when the tisk of flooding occurs, through

measures such as planned an emergency response, salvage and rescue in time; land planning,

rational use of space, enhance the accuracy of forecasting systems and early warning et

According to common trend in the world, flood prevention safety issues and river dikesystem safety are now understood in a broad sense involves the following aspects:

4 Dikes and dike segments ereate “a closed are protection” for residential areas

+ Protected areas of the dike system

~ Safety dike system: Including safety stability of dike and dike segments; safety flood

prevention of protected areas

‘Thus, safety assessments of dike system would include the safety assessment of thestability of closed are protection and the assessment of the appropriateness of existing flooddefenses to ensure the protection of the dikes This assessment ean be done through applying the

Pham Vier Dink ~ L48ULGOIO

general definition of risk above with a purpose: potential risk which was threatened by the flood

to protected area is as small as possible,

Diagram of process of risk analysis,

“The process of risk analysis a system by a probabilistic method includes the following

steps:

+ Description of all components ofthe system;

+ List the types of risks and failures that may occur;

+ Quantitative consequences for al the failures which are capable happened;

++ Identifying and assessing the isk;

+ Conclusions on the results of risk analysisDiagram of general approach to evaluation, risk analysis applications for flood preventionsystem is shown inthe figure below

cag

slewomnya

Figure 3-1: Framework of risk analysis (CUR 141 ~ 1990)

‘The figure above deseribes the components in the risk analysis of a system by

probabilistic method The first the description of the components in the system of flood

prevention structure such as dikes, drains, cond sluice and other components of the structure,Next is the list the types of threats and failures can occur This is an important step in the risk

analysis because of without a failure type (@ failure mechanism) can also seriously affect the

safety of the design Next step is to quantify the consequences for all failures can happen,

3.2.2 Reli ty analysis of components in system

‘The limit state has been the state just before the failure occurred Reliability is the

probability that limit state cannot exceed, Limit states often use to establish the reliability

function, The general formula ofthe limit state function as follow:

Z=R-S enWhere: +R: Strength / resistance to damage;

+8: Load / capacity of eausing damage

The calculation of the failure probability of a component is based on the reliability

function of each mechanism failure Reliability function Z is established based on the limit statecomesponding to failure mechanism which is considered, and it also is a function of many

variables and random parameter Accordingly, Z <0 is considered to be failure occurs: otherwise,failure does not occur f Z gets the other value (Z >0)

“The limi state is a state where the Z n RS plane; It is considered to be the boundary

of failure

The probability of failure is determined by: Pf = P(Z < 0) = P(S > R)

-PfReliability is identified as: PCZ> 0)

Ina simple case, reliability function is linear with basic random variables of the normal

distribution The probability of the failure is calculated through the standard distribution function

‘®y(B) by using value expectation (jt, standard deviation (oz) and reliability index (#=z/ø;) of

reliability function

Pham Vier Dink ~ L48ULGOIO

2<0 Faure zone

220 Safety zone

Figure 3-3: Definition ofthe probability of failure and the reliability index

“The point which is located in the failure zone with the greatest probability density is

considered the “design point” Normally, this point belongs to the failure bounday

point” is important in estimating the probability of failure

3.2.3, Mathematical basis of probabilistic design,

‘There are dhree methods available for calculating the probability of failure when we have

4 given reliability function and given variables and random parameters International technicalthas accepted the following methods:

1) Method level

The design is based on the standards and design guidelines In which liability

parameters are adjusted by the coefficient characteristics, parameters load is increased by the

factor of the load Expressed by the formula:

Fors Gai

Yn

Where: +R: Strength;

+8: Load;

47%: Safety coefficient of strength;

+15: Safety coefficient of load,

In more specific, the characterized of strength parameter and load are calculated byFormula

hạ thee "

`

"Design point” located in the failure zone with a probability density combination ofstrength and load isthe biggest Thus, the value of strength and load at the point of failure is close

to the value at the design point:

S =H, +a ,Po, =p(L+,ØW,)Combining 2 systems of equations above, we have:

Safety coefficient of strength depends on the standard deviation of both strength and

load

66)

2) Method level IT

This method includes several approximate methods to transform the probability

distribution funetion into a normal distribution function or Gaussian distribution To determinethe approximate value of the probability of failure, we need to linearize mathematical theequations related

Depending form of reliability function and distribution of basic random variables, cases of

calculator include:

4) Case 1: Linear reliability function with basic random variables normal distribute

{In this case, the calculation of the probability of failure imple by using expected valueand standard deviation of the basic variables The reliability valu {termined by formula

If the basic random variables X,,X,, X, follow the normal distribution la 1 Zis also

normal distribution function Probability Z <0 is determined through standard distributionfunctions

1) oo

6) Case 2: Nonlinear reliability function:

In the case reliability funetion is a nonlinear function of several independent basic

variables with a normal distribution, the function is not standard distribution Using Taylor'smethods expansion to determine the approximate reliability function Z Approximate expressions