UNIVERSITÉ D’AIX-MARSEILLE ÉCOLE DOCTORALE SCIENCE POUR L’INGÉNIEUR: MÉCANIQUE, PHYSIQUE, MICRO ET NANOÉLECTRONIQUE THÈSE HYDRO-MECHANICAL ANALYSIS OF BREACH PROCESSES DUE TO LEVEE FAILURE PRÉPARÉE À IRSTEA D’AIX-EN-PROVENCE POUR OBTENIR LE GRADE DE DOCTEUR DE L’UNIVERSITÉ D’AIX-MARSEILLE SPÉCIALITÉ MÉCANIQUE DES SOLIDES PAR LIU ZHENZHEN SOUTENUE PUBLIQUEMENT LE 03 JUILLET 2015 DEVANT LE JURY COMPOSÉ DE Frédéric Golay Rapporteur MCF, Université du Sud Toulon Var Didier Marot Rapporteur PR, IUT de Saint-Nazaire Fabien Anselmet Examinateur PR, Ecole Centrale de Marseille Said EI Youssoufi Examinateur PR, Université de Montpellier Stéphane Bonelli Directeur de thèse DR, IRSTEA, Aix en Provence Introduction Floods can have serious consequence in floodplains. Worldwide, many areas can become flooded or are at risk, and numerous people risk being displaced. Determining flood risks is an effective method of ensuring safety against inundation. The accurate analysis of the failure of flood protection structures is the first step in mapping the resulting inundation in a floodplain. Thus, hydro-mechanical analyses of breach processes due to the failure of embankment dams and levees are conducted. As one of the main cause of the serious failure of embankment dams and levees, piping (or the internal erosion of soil) failure process is simulated in Chapter 2. The pipe flow with erosion mechanism is employed into the pipe enlargement model for embankment dams and levees. The hydraulic head variation in the upstream, the trail water conditions in the downstream, the collapse of the pipe top and the transition to a breach are taken into account in the pipe enlargement model. Once a breach is formed, it begins to enlarge downward and laterally. The hydraulic erosion in the breach and episodic retreat of the headcut are considered as controlling mechanisms during breach widening processes. A simply headcut migration model based on the soil tensile strength is presented in Chapter 3 to simulate the critical length of the headcut. Input parameters of this model are: the breach geometry, the soil properties and the flow situations in the breach. Heights of embankment dams ranging from 2 to 12 meters are used to calculate the critical lengths of the headcut under different soil tensile strengths ranging from 0 to 18 kPa. This analytical model is verified by the traditional side slope stability analysis method with three typical embankment dam scales (2, 4 and 6 meters high) in Chapter 4. Due to quick variations of flow streamlines in the breach, distributions of shear stress on the boundary of the breach are complex with the effects of the secondary flow. To accurate estimate erosion processes, a simple numerical model is proposed to calculate averaged lateral and bottom shear stresses and the depth-averaged velocity in Chapter 5. It accounts I for turbulent effects via the dimensionless eddy viscosity coefficient , and secondary flow effects via the dimensionless secondary flow parameters k1 and k2 . A large-scale test is used to validate our numerical model in Chapter 6. The comparisons with measured data are with good agreements. II Contents Chapter 1. Bibliography 1.1. Floods and flood risk ................................................................................................ 3 1.1.1. Floods in China .................................................................................................... 3 1.1.2. Floods in France ................................................................................................. 12 1.2. Breach models of embankment dam and levee failures ...................................... 15 1.2.1. Introduce............................................................................................................. 15 1.2.2. Experimental breach models .............................................................................. 16 1.2.3. Physical breach models ...................................................................................... 20 1.3. Laboratory and field dam breach tests ................................................................. 35 1.3.1. IMPACT project in the EU (from 2001 to 2004) ............................................... 35 1.3.2. Overtopping research in the US ......................................................................... 37 1.3.3. Headcut migration tests ...................................................................................... 42 1.4. Conclusions .............................................................................................................. 46 Chapter 2. Pipe enlargement processes 2.1. Literature review of the failure of embankment dams and levees due to internal erosion and piping .......................................................................................................... 49 2.1.1. Introduction ........................................................................................................ 49 2.1.2. Initiation and continuation of erosion ................................................................ 49 2.1.3. Pipe enlargement ................................................................................................ 50 2.1.4. Formation of breach ........................................................................................... 54 2.1.5. Breach widening ................................................................................................. 55 2.2. Piping flow with erosion ......................................................................................... 55 2.2.1. General introduction of pipe flow ...................................................................... 55 2.2.2. Soil surface erosion by tangential flow .............................................................. 56 2.2.3. Pipe flow with erosion ....................................................................................... 57 I 2.3. Soil erodibility ......................................................................................................... 58 2.3.1. Soil erodibility tests ........................................................................................... 58 2.3.2. Erosion rate coefficient ...................................................................................... 60 2.3.3. Critical shear stress ............................................................................................ 62 2.4. Model for pipe enlargement ................................................................................... 63 2.4.1. Model description .............................................................................................. 63 2.4.2. Model calculation ............................................................................................... 66 2.4.3. Computational algorithm ................................................................................... 69 2.5. Conclusions.............................................................................................................. 69 Chapter 3. Breach widening processes 3.1. Literature review of the breach widening processes ........................................... 73 3.1.1. The formation of a breach .................................................................................. 73 3.1.2. Breach enlargement ........................................................................................... 73 3.1.3. Final breach ........................................................................................................ 80 3.2. The breach width expression ................................................................................. 82 3.2.1. Simplifications of breach geometry ................................................................... 82 3.2.2. Calculation of the breach width ........................................................................ 84 3.2.3. General classification of breach widening ......................................................... 84 3.2.4. The knowledge of the two variables .................................................................. 85 3.3. Headcut migration .................................................................................................. 87 3.3.1. Failure modes ..................................................................................................... 87 3.3.2. Sketch of a headcut ............................................................................................ 89 3.3.3. Failure criterions ................................................................................................ 90 3.3.4. Soil shear strength .............................................................................................. 90 3.3.5. Bending failure calculations .............................................................................. 94 3.3.6. Shear failure calculations ................................................................................. 103 3.4. Analytical results and discussion......................................................................... 109 3.4.1. The specific soil weight ................................................................................... 110 3.4.2. The water head in the breach ........................................................................... 110 3.4.3. The ratio of the depth of erosion to the water head ......................................... 110 3.4.4. Infiltration coefficient ...................................................................................... 111