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Analysis of Liquefaction potential and Slope stability of the Right bank of Red river dikesubjected to earthquake loading

Name: TRAN ANH DUY

Major: Sustainable Hydraulic StructureStudent number: 148ULG015

I hereby declare that this is my own research which was scientifically instructed byAssoc.Prof Nguyen Hong Nam. The research content and results in this master thesis arehonest and unpublished in any previous form or not overlapped with any dissertation. Theinput data in the tables supporting for analysis, comments and assessment are collected bythe author from other sources which was clearly specified in the References.

Besides, my thesis also use some comments and data of other authors, agencies and

organizations with clear citations and source notes.

If there is any fraudulent in the content of my thesis. I would like to take fullresponsibility as prescribed.

Hanoi, November 16", 2016Signature

Tran Anh Duy

Tran Anh Duy — Master Course

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Analysis of Liquefaction potential and Slope stability ofthe Right bank of Red river dikesubjected to earthquake loading

1 would like to express my deep gratitude to my supervisor Associate, Professor. NguyenHong Nam at Thuy Loi University for his full support, expert guidance, understandingand encouragement throughout my study and research, Without his incredible patienceand timely wisdom and counsel, my thesis work would have been a frustrating andoverwhelming pursuit

Additionally, I express my appreciation to my co-supervisor Professor. COLLIN Frédéric

at University of Liege for his valuable comments about this thesis. Thank also goes to Dr.

Pham Quang Tu at Thuy Loi University who teach and support me in Module Foundation‘of Hydraulic Structures and guide me to choose my thesis in this field,

Also, my deep gratitude is to Department of Academie Affairs of Thuy Loi Universityand University of Liege for giving me the golden chance to apply the Mse. Program inmajor of Sustainable Hydrauli <small>ructure</small>

Finally, I would like to thank the Ministry of Science and Technology of Vietnam forproviding the financial support for the experimental work within the framework of thestate-funded research project No. KCO§.23/11-15

November, 2016‘Tran Anh Duy

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Analysis of Liquefaction potential and Slope stability of the Right bank of Red river dikesubjected fo earthquake loading

1.2, The situation of earthquake problem and dike system in Vietnam.1.3, Past studies related to the problem and area

2.3, Modeling the problem of Red river dike ~ modeling method

2.3.1. Overview of modeling method.

2.3.2. Modeling the problem2.33. Output of modeling

CHAPTER 3: TEST MATERIAL, APPARATUS, PROCEDURE AND OUTPUTPARAMETERS.

3.1, Test material

3.2. Dynamic triaxial apparatus

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33. Test procedure

4.3.1. Sample preparation

3.3.2, Water supply and Pressure supply4.3.3. Carbon dioxide (COs) pervasion.4.34. Desair water supply

3.35. Saturation checking4.36. Consolidation

3.37. Cyclic undrained loaling3.4, Output parameters

CHAPTER 4: TEST RESULTS AND DISCUSSION4.1, Experimental results

5.14. Peak ground acceleration

5.2. Modeling liquefaction and slope stability results5.2.1. Liquefaction zone

5.2.2. Parameter studies5.2.3. Slope stability5.2.4. Displacement

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CHAPTER 6: CONCLUSIONS AND RECOMMENDATION.6.1, Achieved results

6.1.1. Experimental results6.1.2. Modeling results62. Existing problem6.3, RecommendationREFERENCES.

ANNOTATION,APPENDIX A,APPENDIX B

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LIST OF FIGURES

Figure 1.1 Earthquake simple visualization (University of California, San Diego, 2013) ..1Figure 1.2 The mechanism of liquefaction (Bhandari, 2015) 2Figure 1.3 Schematic illustration of mechanism of liquefaction inside a levee (Maugeri,2014) 4Figure 1.4 Tokachi earthquake, 2003 (Ehime University, 2015) 4Figure 1.5 Tohoku earthquake, 2011 (Japan) (Ehime University, 2015) 5Figure 1.6 Map of fault system of South East Sea area (Cao Dinh Trieu, 6Figure 2.1 Factor of safety versus time during the earthquake 16Figure 2.2 Modeling of problem for section K73+750 7Figure 23 Diagram of model parameters for each soil layer. 18Figure 2.4 Diagram of modeling intial stress problem, 19Figure 2.5 Diagram of modeling dynamic problem. 19Figure 2.6. Diagram of modeling dike slope stability subjected to earthquake loading....20Figure 2.7 Number of slipping surfaces 20Figure 2.8 Cyclic stress path from B to the collapse surface (QUAKE/W manual, 2010)21Figure 3.1 Sand material dumped at the Hanoi harbor. 23Figure 3.2 Cyclic Triaxial Apparatus DTC ~ 367D, SEIKEN Japan. 2”Figure 3.3 Sand specimen preparation 25Figure 3.4 Water supply and Pressure supply for specimen inside the triaxialcel,... 26Figure 3.5 The system of CO, gas tank and controller 1Figure 3.6 Stresses on the specimen 30Figure 4.1 Soil particle distribution curve of a typical sample from s analysis...33Figure 4.2 Relationship between Cyclic Stress Ratio and Number of Loading Cycles....34Figure 4.3 Relationship between Excess Pore Water Pressure Ratio and Number of

Loading Cycles 34

Figure 4.4 Relationship between Axial Stain and Number of Loading Cycles 35

Figure 4.5 Relationship between Deviatorie Stress and Mean Effective Principal Stress.35

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Figure 4.6 Relationship between Deviatoric Stress and Axial Strain 36Figure 4.7 Relationship between Excess Pore Water Pressure Ratio and Axial Striin...36Figure 4.8. Relationship between Cyelic Stress Ratio and Number of Loading Cyeles....37Figure 4.9 Relationship between Excess Pore Water Pressure Ratio and Number of

Loading Cycles 37Figure 4.10 Relationship between Axial Strain and Number of Loading Cycles 38Figure 4.11 Relationship between Deviatoric Stress and Mean Effective Principal Stess

38Figure 4.12 Relationship between Deviatoric Stress and Axial Strain 39Figure 4.13 Relationship between ‘cess Pore Water Pressure Ratio and Axial Strain ..39Figure 4.14 Relationship between Cyclic Stress Ratio and Number of Loading Cycles...40Figure 4.15 Relationship between Excess Pore Water Pressure Ratio and Number ofLoading Cycles 40Figure 4.16 Relationship between Axial Strain and Number of Loading Cycles 41Figure 4.17 Relationship between Deviatorie Stress and Mean Effective Principal Stress

Figure 4.18 Relationship betveen Deviatorie Stress and Axial Strain a2

Figure 4.19 Relationship between Excess Pore Water Pressure Ratio and Axial Strain ..42Figure 4.20 Schematic Definition of the Number of Cycles Ne for the Specified DA value

44Figure 4.21 Liquefaction curve of soil samples from Hanoi harbor area 4

igure 5.1 Location of the research Red River Dike, Km73+500 ~ Km74+100 46

Figure 5.5 Section

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Figure 5.7 Accel

second 5seration time histor ars for initial 10swith return period of T475 yFigure 5.8 Acceleration time histories with return period of T2475 years 56Figure 5.9 Acceleration time histories with return period of T2475 years for initial 10second 56Figure 5.10 Liquefaction zone, T = 475 years, acceleration record: 475rla 7Figure 5.11 Liquefaction zone, T = 475 years, acceleration record: 475124. 37Figure 5.12 Liquefaction zone, T = 475 years, acceleration recond: 475:3a 58igure 5.13 Liquefaction zone, T = 475 years, acceleration record: 475314 38Figure 5.14 Liquefaction zone, T= 475 years, acceleration record: 475424 5Figure 5.15 Liquefaction zone, T = 475 years, acceleration record: 475434 9Figure 5.16 Liquefaction zone, T = 2475 years, acceleration record: 2475rla 39Figure 5.17 Liquefaction zone, T = 2475 years, acceleration record: 2475124, 9Figure 5.18 Liquefaction zone, T= 2475 years, acceleration record: 247513 0Figure 5.19 Liquefaction zone, T= 2475 years, acceleration record: 2475914 0Figure 5.20 Liquefaction zone, T = 2475 years, acceleration record: 2475s2a 0Figure 5.21 Liquefaction zone, T= 2475 years, acceleration record 61Figure 5.22 Liquefaction zone, T = 475 years, acceleration record: 475s3a, WL: +10.5..63Figure 5.23 Liquefaction zone, T = 2475 years, acceleration record: 475s3a, WL: +13.463Figure 5.24 Liquefaction zone, T = 2475 years, acceleration record: 2475s3a, WL: +105

Figure 5.25 Liquefaction zone, T = 2475 years, acceleration record: 247533a, WL: +13.4

6Figure 5.26 Slope stability, safety factor K = 2.846, acceleration record: 475r1a. 65gure 5.27 Slope stability, safety factor K = 2,863, acceleration record: 47512a. 65Figure 5.28 Slope stability, safety factor K = 2.845, acceleration record: 47513a. 6Figure 5.29 Slope stability, safety factor K = 2.737, acceleration record: 475914 66Figure 5.30 Slope stability, safety factor K = 2.94, acceleration record: 475s2a 66

Figure 5.31 Slope stability, safety factor K = 2.882, acceleration record: 475s3a 66

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Figure 5.32 Slope stability, safety factor K = 2.613, acceleration record: 2475rla...6?

Figure 5.33 Slope stability, safety factor K = 2.799, acceleration record: 2475124...6?

Figure 5.34 Slope stability, safety factor K = 2,610, acceleration record: 2475134...67

Figure 5.35 Slope stability, safety factor K = 2.697, acceleration record: 24758la...8

Figure 5.36 Slope stability, safety factor K = 2.739, acceleration record: 2475924...68

74, acceleration record: 241593a...68

Figure 5.37 Slope stability, safety factor KFigure 5.38 Total displacement (m), acceleration record: 475r1a 70Figure 5.39 Total displacement (m), acceleration record: 475/24 70Figure 5.40 Total displacement (mm), acceleration record: 415r3a 70

igure 5 41 Total displacement (m), acceleration record: 475914 7

Figure 5.42 Total displacement (m), acceleration record: 475:2a 1Figure 5.43 Total displacement (m), acceleration record: 475838 nFigure 5.44 Total displacement (m), acceleration record: 2475rla nFigure 5.45 Total displacement (mm), acceleration record: 2475:2a nFigure 5.46 Total displacement (m), acceleration record: 2475:3a nFigure 5.47 Total displacement (m), acceleration record: 2475914 7

Figure 5.48 Total displacement (m), acceleration record: 2475524 B

Figure 5.49 Total displacement (m), acceleration record: 2475338 B

APPENDIX FIGURES.

Figure A.1 Initial horizontal effective stress (KPa), acceleration record: 47533a 2Figure A.2 Initial vertical effective stress (kPa), acceleration record: 475s3a saFigure A.3 Dynamic horizontal effective stress (KPa), acceleration record: 47593a...2Figure A.4 Dynamic vertical effective sess (kPa), acceleration record: 475s3a 83Figure A.5 Liquefaction zone, acceleration record: 475834 83Figure A.6 Horizontal displacement (m), acceleration record: 475334 83Figure A.7 Vertical displacement (m), acceleration record: 475s3a 83Figure A.8 Total displacement (m), acceleration record: 475934 4“Figure A.9 Slope stability, safety factor K = 2.882, acceleration record: 475s3a. 84

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Figure B.1 Initial horizontal effective stress (kPa), acceleration record: 2475332Figure B.2 Initial vertical effective stress (KPa), acceleration record: 2475s3a,Figure B.3 Dynamic horizontal effective stress (KPa), acceleration record: 2475s3aFigure B.4 Dynamic vertical effective stress (kPa), acceleration record: 2475s3a,Figure B.5 Liquefaction zone, acceleration record: 2475s3a.

Figure B.6 Horizontal displacement (m), acceleration record: 2475534.Figure B.7 Vertical displacement (m), acceleration record: 247583,Figure B.8 Total displacement (m), acceleration record: 2475534

474, acceleration record: 2475534.Figure B.9 Slope stability, safety factor K

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LIST OF TABLES

Table 3.1 Saturation degi ulation 28Table 3.2 Necessary diagrams for the analysis of triaxial test 31Table 4.1 Soil particle distribution table from sieve analysis (ASTM D422-63) 32‘Table 4.2 Input data from 4 samples of the harbor soil. 33Table 4.3 Analysis data from 4 samples of the harbour soil 4‘Table 5.1 Soil properties of each layers 52‘Table 5.2 Peak Ground Acceleration (PGA) value of the return period of 475 years at theboring holes 4‘Table 5.3 Peak Ground Acceleration (PGA) value of the return period of 2475 years atthe boring holes 54‘Table 5.4 Liquefaction calculation results of Red river dike, section K73+750, 6tTable 5.5 The water level corresponding to the warning level at Hanoi river đike...62‘Table 5.6 Liquefaction potential results corresponding to different water levels at Hanoiriver dike 6Table 5.7 Slope stability results of Red river dike, section K73+750. 69‘Table 5.8 Displacement results of Red river dike, section K73+750. 14

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CHAPTER 1: INTRODUCTION1.1. The theoretical basis of liquefaction

LLL. Earthquake definition

Earthquake is a dangerous natural disaster that can ruin the structures located not‘only on the ground but also underground, Earthquakes can be understood as the

vibrations caused by rocks breaking under stress. The underground surface along

which the rock breaks and moves is called a fault plane (Figure 1.1). The starting

point of fracturing rocks or the actual point, where the fault rupture begins, is

‘called the hypocenter. Directly above the hypocenter, the point on a planeUssurface is called the epicenter or the focus of an earthquake (University of

California, 2013),

Figure 1.1 Earthquake simple visualization (University of California, San Diego, 2013)1.1.2. Liquefaction phenomenon

Due to the earthquake loading, the pore water pressure increases significantly

which leads to the volume decrease of soil particle. ‘Therefore, load bearing

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capacity and shear resistance of soil are decreased, called as soil liquefactionLiquefaction is considered as the transition of state that the soil changes fromdiscrete state (0 liquid state. It can be represented that the shear stress of saturateddiscrete soil decrease to equalize with the shear stress subjected to dynamicloading, which makes the soil transfer to liquid state.

In normal state cach soil particle interacts with the other surrounding particles, andthe interaction force is formed by the loading on the ground and self-weights of theabove particle layers, Additionally, this force makes the particles interact with eachother at a position without movement, and it also creates the load bearing capacityof soil. In terms of saturated soil, the interaction force acts on the particles and porewater as seen in Figure 1.2a.

Note: - The blue column in the right side represents for pore water pressure

‘The length of the arrow represents for the magnitude of interaction forces

between particles.

At the initial time, the interaction of particles and pore water pressure is relativelylow as seen in Figure 1.2b. When earthquake happens, it causes strong stress inshort period. The seismic waves transmit through the saturated soil layers, whichchanges the position of particles and distribute them to the new order. The discreteparticles have the trend to move closer and make the soil denser. At that time, these

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particles take the place and push water away in the pore, which makes the porewater pressure increase, Therefore, water tends to dissipate around where the waterpressure is less than,

‘The saturated soil does not have enough time to drain out the water, so the pore‘water pressure increase and the friction connection of those particles is weakened(Figure 1.2c). When the pore water pressure increases to the certain value, theconnection of particles will be lost and the soil is in the liquid state, called as soilliquefaction (Bhandari, 2015),

‘Therefore, the soil liquefaction phenomenon happens, which may cause the

deformation and destruction of the structure. Evaluation of soil liquefaction

potential subjected to earthquake loading is an important aspect of geotechnical

engineering practice,

1.1.3. Liquefaction of river dikes

It is obviously that the seismic motion of earthquake might cause damages to manystructures. These structures include river dikes or levees which display in cracks,settlement or sand boils caused by liquefaction, The in situ tests about earthquake‘on embankments resting on loose saturated sand show that the major cause of dikesettlement is the lateral deformation of liquefied soil beneath dike away from theembankment centerline (Ehime University, 2015). The mechanism of liquefactionof river dike soil (Figure 1.3) can be summarized as follows:

— Construction of levee with highly compressive and less permeable soilscauses consolidation and settlement on foundation ground,

— Rain and underground water infiltrated through the dike will beaccumulated in the bowl and formed as the saturated zone,

During the strong earthquake, the sandy soils in saturated zone might beliquefied which causes the significant deformation to the levee.

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Conslidation Original shape of levee

CT lies

Uniquetiable cohesive soft soil

Figure 1.3 Schematic illustration of mechanism of liquefaction inside a levee

(Maugeri, 2014)

When the liquefaction phenomenon exits in the foundation, the foundation has no

load bearing capacity, which leads to the settlement, horizontal displacement and

cracks on the river dike. Additionally, in terms of high ground water level, theliquefaction happens in dike body leading to the loss of connection capability andinitial shape of construction, Hence, it causes the deformation and destruction of

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— The liquefied levee slope slide down and spread laterally with convex toes

Figure 1.5 Tohoku earthquake, 2011 (Japan) (Ehime University, 2015)

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1.2. The situation of earthquake problem and dike system in Vietnam

In recent years, the frequency of earthquake in Vietnam is relatively high, especiallyin 2010 with the biggest earthquake reached 5.0 Richter. Some regions are noticed inthe fault line with 6.0 — 7.0 Richter earthquake potential such as Red ~ Chay Riverfollowing the Figure 1.6. In the past, Vietnam has recorded two big earthquakes: DienBien earthquake (1935) with 675 Richter at Ma river fault line and Tuan Giáoearthquake (1983) with 68 Richter at Son La fault line. When earthquake happens,soil is easily liquefied in the presence of water such as along rivers, lakes, bays,‘Therefore, hydraulic structures like embankment, dike are most commonly affected

and damaged when soil liquefaction happens,

Figure 1.6 Map of fault system of South East Sea area (Cao Dinh Trieu, 2005)

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The stability studies of in-situ material dikes or embankments filled have beenimplemented in hydraulic construction for 50 years. However, the stability studies of‘earth works due to earthquake effects are very limited, mainly for concrete dam,

Dike is the structure against river flood or seawater. The total length of dike inVietnam is more than 13,200km, including 10,600km of river dikes, 2,600km of seadikes and 2,500km of special dikes for flood control. It is nec: ty to regularlyrepair and upgrade these special dikes, especially in the condition of climate changeand sea level rise inthe future, Currently, Vietnam dike system has been designedagainst storm grade 9 with the maximum tide of $%%, Many dikes have beentructed on the thí

sand layer which is easily liquefied if the strong earthquake

happens. Additionally, there are some dikes on the soft soil foundation leading topotential instability due to the poor filling soil quality by using handerafted fillingmethod (Nam 1997 & 1998). The government has recently approved two big projects:sea dike improvement project, from Quang Ninh to Quang Nam provinces and fromQuang Ngai to Kien Giang provinces and river dike improvement project at 19provinces having the decentralized dikes, with total funds above 50 thousand billiondong, lasted until 2020.

Note that Vietnam construction law has few rules and standards for taking account ofsoil liquefaction in hydraulic construction design such as TCXDVN 285-2002,14TCN 157-2005, However, the stability evaluation method was mainly based on thepseudo-static method with earthquake acceleration coefficient corresponding to the

iruction grade, Recently, designing constru

mentioned in TCXDVN 375-2006, which was compiled based on EUROCODE 8Nevertheless, the limitations of TCXDVN 375-2006 do not consist of seismic

n under earthquake loading wasrecordings, peak ground acceleration with the earthquake return period of more than475 years in comparison with EUROCODE 8,

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“The reasons of the selection of Red river dike at Hanoi as a ease study in this thesisare based on the following basis:

— Hanoi dike system has the special mission in protecting Hanoi ~ the center ofeconomic, culture, politics of Vietnam with the population of 6.45 millionpeople (Census Steering Committee on Population and Housing. 2010),

— Hanoi was in the zone of fault fine Red river ~ Chay river; some historicalstrong earthquakes happened with grade 7, grade 8 in 1277, 1278, 1285

(earthquake magnitude seale MSK-64);

— The soil stratigraphy of dike foundation consist the thick sand layer which iseasily iquefied when strong earthquake happens:

— Some water supply projects will be constructed,1.3. Past studies related to the problem and area

In order to have a general view of the problem and study area, so we should refer tosome researches related to the study area, application in the world

Nam (2015) studied and modeled the liquefaction potential and stability of an actualriver dike at Hanoi under the different earthquake secnarios according to FiniteElement method, using Quake/W software. The analysis results showed that with thethick sand layer, the right bank of Red river dike has the liquefaction potential of soilsoil inside dike with the earthquake return period of 475 years and 2475 years, whichendangers the dike and the constructions on it.

Nam (2012) analyzed the cause of slope failure of the right bank of Red river,‘corresponding to K29+850 ~ K304050 Red river dike at Son Tay. The analysis results

showed that the main causes of the failure of the right bank of Red river was theplacement of heavy sand pile and the soft soil 2a in the foundation through critical‘ross section 2 The liquefaction phenomenon was not considered because of no‘earthquake,

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Duong (2012) studied the liquefaction mechanism of in-situ material dam Nam KhauHu, Dien Bien province. The analysis results showed that the in-situ material dam

was totally complied with dam quality, eliminated the seepage flow drawbacks and

the liquefaction risk if earthquake happens.

“Tam- etal, (2011) analyzed the liquefaction potential of Red river dike Km294900 toKm304050 in Son Tay district, The analysis results showed that the level ofearthquake was corresponding to the scope of liquefaction area, The result with‘employing the linear equivalent model was smaller than that with the Tinear elastie

Binh and Phuong (2008) studied experimentally the change of Pore Water Pressure

for sedimentary clays Holocen at Red River Delta subjected to dynamic loadingeycles. However, the experimental results were still limited, and the accuracy of

results, the experimental condition and the apparatus need to be clarified

Youd: etal. (2001) summarized the method of evaluation of liquefaction resistance ofsoil known as simplified procedure, The CPT and SPT provide detailed soilstratigraphy and robust filed-data based liquefaction resistance curve. Procedures for

evaluation of liquefaction resistance beneath sloping ground or embankments have

not been developed (slope greater than 6%).

Nghia (2008) study and determine the coefficients of soil dynamic to apply for‘computing the works under dynamie loading. Stress waves were loading transmissionincluding compress wave (P-wave) and shear wave (S-wave). The liquefaction was

‘due to expansion causing shear deformation. The shear resistance module D was

calculated approximately through Vane Shear Test.

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1A, Resi ‘ch objectives

‘The main objective of this research can be represented as follows:— Determining the liquefaction risk due to strong earthquake

Evaluating the liquefaction potential of Red river dike foundation for differentcalculation scenarios.

Slope Stability assessment of Red river dike caused by earthquake.

— Recommendation for the improvement of the safety of Red river dike when

strong earthquake happens.1.5. Research methodology

The research can be implemented by two methods: experimental method and‘numerical modeling method based on Finite Element Method (FEM). The following

approach will be implemented in the research:

Collecting the ne ry data from all related sourees including.+ Basic data of topography, hydrology, water level

<small>+ Soil properties ofeach layer forall boring holes</small>

<small>+ Historical records of earthquake and acceleration time history in the study</small>

~ Clarify the formation mechanism of liquefaction

~ Experimental studies using dynamic wiaxial apparatus on Red river sandsamples.

Modeling of liquefaction and slope stability based on Finite Element Method,calibrating and validating using measured data

= As

and determine the safety of Red river dike based on the measured and

simulated results

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Chapter 4: Test results and discussion

Chapter 5: Liquefaction modeling of Red river dike and Slope stability analysis

Chapter 6: Conclusion and Recommendation

Appendix A: Liquefaction results corresponding to 475-year earthquake returnperiod

Appendix B: Liquefaction results corresponding to 2475-year earthquake retumperiod

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CHAPTER 2: LIQUEFACTION ANALYSIS AND SLOPE STABILITY

THEORETICAL BASIS.2.1. Overview of analysis methods

In terms of soil liquefaction analysis and assessment, there are many methods toimplement in the past studies in all over the world such as simplified procedure,experimental method, numerical modeling method and physical modeling methodOver the past 45 years, a methodology termed the “simplified procedure” (Seed and1d 1971) has evolved as a standard of practice for evaluating the liquefactionresistance of soils, The simplified procedure was developed from empirical

evaluations of field observatio

s and field and laboratory test data, Two variables arerequired for evaluation of liquefaction resistance of soils: the seismic demand on asoil layer, expressed in terms of CSR, and the cap: ity of the soil to resistliquefaction, expressed in terms of CRR. The equation 2-1 for factor of safety (FS)against liquefaction is writen in terms of CRR and CSR as follows:

* đụ, and o’y, are total and effective vertical overburden stresses

<small># r= stress reduction coefficient= CRRis</small>

be determined based onin-situ test data (SPT data, CPT data or V,y data orcyclic resistance ratio for magnitude 7.5 earthquakes, which canexperimental test data (cyclic triaxial test, simple shear test or hollowcylinder torsional shear test)

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This research will be implemented by combining the experimental method and thenumerical modeling method.

To begin with, the experimental method uses the laboratory experimental apparatus 10study the liquefaction parameters (as described in section 2.2), mechanism and soilbehavior due to cyclic loading. Firstly, the liquefaction parameters need to be clarified.to have the general view about the parameters obtained from the test. After that, the

Cyclic Triaxial apparatus, Following the test procedure, the output data of triaxial test‘Undrained Triaxial Test will be implemented with the sand samples by usingcan be determined and analyzed to get the relationship between liquefaction

parameters corresponding to the representative diagrams,

Additionally, these above output data of experiment and the representative diagramswill be applied as the input data in modeling problem based on the numericalmodeling method. First of all, the model will be set up following Finite Elementmethod with the specified boundary conditions and the necessary input parameters.Hence, the model results can be analyzed more clearly with the accurate figures andsummarized in the tables.

2.2, Experimental methodLiquefaction parameters

+ Cyclic Stress Ratio, CSR

‘The relationship between density, cyclie stress amplitude and number of cyclesto liquefaction failure can be expressed graphically by laboratory cyelicstrength curves. Cyclic strength values are normalized by the initial effectiveoverburden pressure to produce a eycle stress ratio (CSR), For the eyelic triaxial test, the CSR is defined as the ratio ofthe maximum cyclic shear stress tothe initial effective confining pressure (2-1).

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CSR = 4/2,

<small>beoF Exce</small>

‘To quantify pore pressure build-up during a tri-axial test, the excess pore waterpressure ratio Ry is often used. This can be defined as the ratio of excess porepressure change during loading to the effective stress applied at the beginningof loading (2-2)

* DeViatoric Stress versus Mean Effective Principal Stress, q~ p`

During cyclic triaxial testing

diagram when analyzing soil behavior because of the different circles changingboth in size and position. Therefore, in order to picture stress condition, thedeviatoric stress, q is represented as a function of mean effective stress, p”

it is impractical to use Mohr's circle in o-t

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2.3. Modeling the problem of Red river dike ~ modeling method2.3.1. Overview of modeling method

In order to understand clearly about the liquefaction potential and slope stability ofcase study, the numerical modeling using the Finite Element Method (FEM) shoutdbe applied by one of the most common geotechnical software = moduleQUAKE/W in GeoStudio 2007 -developed by GEO-Slope International Ltd,Canada, This software supports for analyzing the response and behavior of earthstructures subjected to earthquake shaking including:

‘© The movement, internal forees during the shaking

‘© The generation of excess pore water pressure‘© The potential reduction of the soil shear strength

© The effect on stability

The Finite Element Stre s-based method is applied to evaluate the stability

variation due to ground shaking during an earthquake (SLOPE/W manual, 2008)

“The stresses can come from a QUAKE/W dynamic finite element analysis thesame as they can from a static stress analysis. The stresses computed during adynamic earthquake analysis can be saved at regular intervals during the shaking,‘The Finite element stress can be imported into a conventional limit equilibrium

analysis, The stresses ơ,, 05, and ty, are known within each element, and the

normal and mobilized shear stresses can be computed at the base mid-point of each

slice, Therefore, the forecan be integrated over the length of the slip surface to,

determine a stability factor as formula 2.5.

<small>- S; is the total available shear resistance</small>

- Swsurface

the total mobilized shear along the entire length of the slip

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A factor of safety then can be computed for each moment in that that the stressesare available, and in the end a plot of factor of safety versus time graph can becreated, as shown in Figure 2.1. This type of plot can be created for cach and everytrial slip surface.

Factor of Safety vs. Time

Figure 2.1 Factor of safety versus time during the earthquake

‘The Finite element based approach overcomes any of the limitations inherit in a

limit equilibrium analysis, and it has many advantages as follow

‘There is no need to make assumptions about interslice forces

‘The stability factor is deterministic once the stresses have been computed,sand consequently, there are no iterative convergence problems.

‘The issue of displacement compatibility is satisfied.

‘The computed ground stresses are much closer to reality,

‘Stress concentrations are indirectly considered in the stability analysis,Soil-structure interaction effects are readily handled in the stability analysis

Dynamic stresses arising from earthquake shaking can be directly

considered in a stability analysis

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2.3.2. Modeling the problem

Based on the cross-sections following the topographical and geologicalinvestigation document of Red river dike Km73+500 to Km74+100, TLU (2015),the section K734750 is selected to model and analyze with maximum historicalflood level (+13.4) in 1971 at the river side and no water at the land side. Figure22 illustrates the mesh and boundaries of section K73+750 of Red river dike

Depth (m)

Figure 2.2 Modeling of problem for section K73+750

After determining the geometry and mesh of problem, the soil behaviour modelneed to be specified with linear elastic model for all layers. According to thegeological document, some required soil properties were determined, including:

‘+ Unit weight, (7)<small>+ Poisson ‘s ratio, (V)</small>+ Damping ratio, (Dy

+ Cyclic number function, (CSR = N

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“The soil behaivor model is presented in the Figure 2.3 with the specified value ofmodel parameters for each soil layer.

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analyze the slope stability based on FEM.

analyze the slope stability for the downstream slope sn in the Figure 26,

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<small>‘SECTION Kmr2750,</small>

Figure 2.6, Diagram of modeling dike slope stability subjected to earthquake loading‘The most critical slip surface is selected from the stability factor result with thedifferent assumed slipping centers and slipping radius for the different timeperiods. For each time period, the number of analysis slipping surface is 1331slipping surfaces by selecting number of radius increments equal 10, The totalnumber of slipping are is 1331x2000/10=266200 potential sliding arcs.

<small>Fie Hếp</small>

fl suoPE/w- 3

<small>ata ie Lata 13417327505Posh: Fite Eirnet Sope Say</small>

<small>emu Stablty Factor——</small>

RE Matha 3578

SoSufeces: 1301 of1391<small>—.</small>

Figure 2.7 Number of slipping surfaces

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2.3.3. Output of modeling2.3.3.1, Liquefaction zone

Loose sand fundamentally has a collapsible soil-grain structure, and when the

srain-strueture collapses the shear strenth under undrained conditions may

diminish to what is known as the steady-state strength, The soil liquefaction

behavior can be described in the context of a q-p" diagram (shear stress vesus

‘mean principal stress), A collapse surface definition together with a specifiedsteady-state strength can optionally be used in QUAKE/W to flag elements as“Tiquefied” and assign these elements a steady-state strength in SLOPE/Wstability analysis or a SIGMA/W stress re-distribution analysis. The excess

pore water pressure will continue to increase until the stress cyclic path reaches

the collapse surface, Then, the soil will liquefy and the strength falls along the

collapse surface to the steady state point.

Figure 2.8 Cyclic stress path from B to the collapse surface (QUAKEW

manual, 2010)

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The field variable of a stress/deformation problem is displacement, which isrelated to the strain vector through

te) = IEI{}

[B] = strain matrix

uy = nodal displacement in x-and y-diteetion, respectively

“The deformed mesh presents a clear picture of displacements for a single time

<small>step.</small>

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CHAPTER 3: TEST MATERIAL, APPARATUS, PROCEDURE AND.OUTPUT PARAMETERS

By applying the modeling analytical method, the experiment results in the laboratory‘will play the vital role in not only the next step of analysis and modeling but also the

general results of this research, Therefore, we need (0 figure out the general

characteristics of specimens, the experiment apparatus, the method and the output oftriaxial test

3.1. Test material

‘The tested Red river sand samples were taken at the area of Hanoi harbor, Hanoi city(Figure 3.1). The material was retrieved from the Red river dike’s sandy subsoil layerby extracting it from the river bottom bed using machine with high pressure andpumping it up tothe stilling basin in the river upper bank. The test material was takenby using thin-walled tube samplers after removing ground surface,

Figure 3.1 Sand material dumped at the Hanoi harbor

3.2. Dynamic tri

The employed apparatus is Cyclic Triaxial Apparatus, the model DTC-367D‘manufactured by SEIKEN Company, Japan (Figure 3.2). This apparatus consists of aTran Anh Duy ~ Master Course <small>2</small>

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triaxial cell, cell pressure and back pressure control devie. a data acquisition andrecording system for axial load, axial displacement, volume change, and pore water

pressure of specimen, The whole machine is connected to a laptop through data

amplifiers and Sensor Interface including a sampling software in order to obtain theraw test data

Figure 3.2 Cyclic Triaxial Apparatus DTC ~ 367D, SEIKEN Japan3.3. Test procedure

‘The method used for carrying out the test is followed the JGS2000 “Method for Cyclic Undrained Triaxial Test on Soils

standard: IGS

0541-Following is thedescription of test procedure employed in this study

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3.3.1. Sample preparation

‘The red river sand sample collected at the field was set in accordance with the JGS

standard: JGS 0520-2000 “Preparation of Soil Specimens for Triaxial Test” as seen

in Figure 343

‘The cylindrical specimen was prepared with the initial dimension: diameter

D=50mm, height H=100mm. The specimen was formed by pluviating sand

particles through air in which air-dried sand falls through a funnel with the desired

calculated height of fall maintained constant by using the string Hiner to get the

uniform relative density Dr based on the following formula (3-1):

Dr = —— 40)

_Smax~Emin.

ep: Initial void ratio

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‘maxi Maximum void ratio.

nia? Minimum void ratio

Note that: the initial void ratio ep was determined based on density at site.3.3.2. Water supply and Pressure supply

After the specimen preparation, the de-aired water was supplied to the cylindricaltank by opening the valve Confining water. Until water reached the target level inorder to guarantee that the specimen is submerged, but it is not higher than the

upper part of membrane attached to the top cap in case that water might go inside

the specimen (Figure 3.4)

‘Then, we supplied the initial confining pressure of 30 kPa for this cylindrical tank.

Figure 3.4 Water supply and Pressure supply for specimen inside the triaxial cell

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3.3.3. Carbon dioxide (CÓ,) pervasion

After supplying the tial confining pressure in cylindrical tank, the CO; gas waspervaded into the specimen for 30 minutes with the recommended rate of 2-3bubbles per second following the JGS 0520-2000. The reason for CO; pervasion isthat the CO, gas goes through the bottom porous stone with the monocular mass

(44) being higher than air (-29), which leads to the air pump through the upper

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3.3.5. Saturation checking

We check the saturated condition of the specimen based on the B value which was

measured by the ratio of the pore water pressure (PWP) and ell pressure (CP) by

Firstly, we increased the back pressure to get 80kPa of CP and SOkPa of PWP.

Secondly, we locked the valve for undrained condition and increase the cell

pressure to 150kPa, then we checked the measured value of PWP by the samplingsoftware as shown in the Table 3.1. Then, we decreased the cell pressure back t0S0kPa and released the valve. The process was repeated with cách increment of

50kPa until the accepted B value was greater than 95%.

Table 3.1 Saturation degree calculation

‘Trial time Ist 2

Phase Initial Final Initial Final

Cell Pressure (kPa) 80 150 130 200Back Pressure (kPa) 50 7 100 168

Saturation B (%) 95.71 97.14

3.3.6. Consolidation

We released the load cell to take isotropic consolidation for about 30 minutes, and

then recorded the data from burette and measurement device.

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3.3.7. Cyclic undrained loading

In the cyclic loading stage, the sinusoidal cyclic load with frequency of 0.1 Hz wasapplied under undrained condition. ‘The load amplitude values were varied for eachspecimen. We recorded the data until the specimen was liquefied with certainnumber of loading cycles. The condition for liquefaction is that the excess pore‘water pressure Ru reaches 95% or the double amplitude of axial strain, is above5% UGS 0541 ~ 2000).

When conducting the liquefaction test, the load frequency and magnitude were

controlled by Pneumatic Servo Controller E0-260. From this machine, a signalvoltage would be sent to the piston to apply the force in the load cell. The SensorInterface would receive the results and transfer it to the computer so that the‘measured data was recorded and controlled by the program DCS-10A ElectronicInstrument

3.4, Output parameters

‘The output data obtained when performing the cyclic triaxial test include:

* Piston force: Fc (KIN) measured by Strain Amplifier DPM-911B,« _ Conlining pressure: ø,„¿ (kPa) measured by sensor PGM-10KE,‘© Pore pressure: u (kPa) measured by sensor PGM-10KE

‘External vertical displacement: LD (mm) measured by ODC-25

‘© Small displacement: SD (mm) measured by Model LP-200

+ Elapsed time: ¢ (s) measured by DCS-10A Electronic Instrument

* Volume change: AV (ml) measured by burette and OUTPUT (V)

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