Geotechnical Engineering of Dams

ISBN-13: 9781138000087 / Angielski / Twarda / 2014 / 1348 str.

Robin Fell; Patrick MacGregor; David Stapledon

Opis

Geotechnical Engineering of Dams, 2nd edition provides a comprehensive text on the geotechnical and geological aspects of the investigations for and the design and construction of new dams and the review and assessment of existing dams. The main emphasis of this work is on embankment dams, but much of the text, particularly those parts related to geology, can be used for concrete gravity and arch dams. All phases of investigation, design and construction are covered. Detailed descriptions are given from the initial site assessment and site investigation program through to the preliminary and detailed design phases and, ultimately, the construction phase. The assessment of existing dams, including the analysis of risks posed by those dams, is also discussed. This wholly revised and significantly expanded 2nd edition includes a lengthy new appendix on the assessment of the likelihood of failure of dams by internal erosion and piping. This valuable source on dam engineering incorporates the 200+ years of collective experience of the authors in the subject area. Design methods are presented in combination with their theoretical basis, to enable the reader to develop a proper understanding of the possibilities and limitations of a method. For its practical, well-founded approach, this work can serve as a useful guide for professional dam engineers and engineering geologists and as a textbook for university students.

Spis treści

Author Biographies 1 Introduction 1.1 Outline of the book 1.2 Types of embankment dams and their main features 1.3 Types of concrete dams and their main features 2 Key geological issues 2.1 Basic definitions 2.2 Types of anisotropic fabrics 2.3 Defects in rock masses 2.3.1 Joints 2.3.2 Sheared and crushed zones (faults) 2.3.3 Soil infill seams (or just infill seams) 2.3.4 Extremely weathered (or altered) seams 2.3.5 The importance of using the above terms to describe defects in rock 2.4 Defects in soil masses 2.5 Stresses in rock masses 2.5.1 Probable source of high horizontal stresses 2.5.2 Stress relief effects in natural rock exposures 2.5.3 Effects in claystones and shales 2.5.4 Special effects in valleys 2.5.5 Rock movements in excavations 2.6 Weathering of rocks 2.6.1 Mechanical weathering 2.6.2 Chemical decomposition 2.6.3 Chemical weathering 2.6.3.1 Susceptibility of common minerals to chemical weathering 2.6.3.2 Susceptibility of rock substances to chemical weathering 2.6.4 Weathered rock profiles and their development 2.6.4.1 Climate and vegetation 2.6.4.2 Rock substance types and defect types and pattern 2.6.4.3 Time and erosion 2.6.4.4 Groundwater and topography 2.6.4.5 Features of weathered profiles near valley floors 2.6.5 Complications due to cementation 2.7 Chemical alteration 2.8 Classification of weathered rock 2.8.1 Recommended system for classification of weathered rock substance2.8.2 Limitations on classification systems for weathered rock 2.9 Rapid weathering 2.9.1 Slaking of mudrocks 2.9.2 Crystal growth in pores 2.9.3 Expansion of secondary minerals 2.9.4 Oxidation of sulphide minerals 2.9.4.1 Sulphide oxidation effects in rockfill dams – some examples 2.9.4.2 Possible effects of sulphide oxidation in rockfill dams 2.9.4.3 Sulphide oxidation – implications for site studies 2.9.5 Rapid solution 2.9.6 Surface fretting due to electro-static moisture absorption 2.10 Landsliding at dam sites 2.10.1 First-time and “reactivated’’ slides 2.10.1.1 Reactivated slides 2.10.1.2 First-time slides 2.10.2 Importance of early recognition of evidence of past slope instability at dam sites 2.10.3 Dams and landslides: Some experiences 2.10.3.1 Talbingo Dam 2.10.3.2 Tooma Dam 2.10.3.3 Wungong Dam 2.10.3.4 Sugarloaf Dam 2.10.3.5 Thomson Dam 2.11 Stability of slopes around storages 2.11.1 Vital slope stability questions for the feasibility and site selection stages 2.11.1.1 Most vulnerable existing or proposed project features, and parts of storage area? – Question 1 2.11.1.2 Currently active or old dormant landslides? – Questions 2 and 4 to 72.11.1.3 Areas where first-time landsliding may be induced (Questions 3 to 7) 2.11.1.4 What is the likely post failure velocity and travel distance? 2.11.1.5 What is the size of impulse waves which may be created? 2.12 Watertightness of storages 2.12.1 Models for watertightness of storages in many areas of non-soluble rocks 2.12.2 Watertightness of storage areas formed by soluble rocks 2.12.3 Features which may form local zones of high leakage, from any storage area 2.12.4 Watertightness of storages underlain by soils 2.12.5 Assessment of watertightness 2.12.5.1 Storages in non-soluble rock areas – assessment of watertightness 2.12.5.2 Storages in soluble rock areas – assessment of watertightness 2.12.5.3 Storages formed in soils – assessment of watertightness 2.12.6 Methods used to prevent or limit leakages from storages 3 Geotechnical questions associated with various geological environments 3.1 Granitic rocks 3.1.1 Fresh granitic rocks, properties and uses 3.1.2 Weathered granitic rocks, properties, uses and profiles 3.1.3 Stability of slopes in granitic rocks 3.1.4 Granitic rocks: check list 3.2 Volcanic rocks (intrusive and flow) 3.2.1 Intrusive plugs, dykes and sills 3.2.2 Flows 3.2.2.1 Flows on land 3.2.2.2 Undersea flows 3.2.3 Alteration of volcanic rocks 3.2.4 Weathering of volcanic rocks 3.2.5 Landsliding on slopes underlain by weathered basalt 3.2.6 Alkali-aggregate reaction 3.2.7 Volcanic rocks (intrusive and flow) check list of questions 3.3 Pyroclastics 13.3.1 Variability of pyroclastic materials and masses 3.3.2 Particular construction issues in pyroclastics 3.3.3 Pyroclastic materials – check list of questions 3.4 Schistose rocks 3.4.1 Properties of fresh schistose rock substances 3.4.2 Weathered products and profiles developed in schistose rock 3.4.3 Suitability of schistose rocks for use as filter materials, concrete aggregates and pavement materials 3.4.4 Suitability of schistose rocks for use as rockfill 3.4.5 Structural defects of particular significance in schistose rocks 3.4.5.1 Minor faults developed parallel and at acute angles to the foliation 3.4.5.2 Kink bands 3.4.5.3 Mica-rich layers 3.4.6 Stability of slopes formed by schistose rocks 3.4.7 Schistose rocks – check list of questions 3.5 Mudrocks 3.5.1 Engineering properties of mudrocks 3.5.2 Bedding-surface faults in mudrocks 3.5.3 Slickensided joints or fissures 3.5.4 Weathered products and profiles in mudrocks 3.5.5 Stability of slopes underlain by mudrocks 3.5.6 Development of unusually high pore pressures 3.5.7 Suitability of mudrocks for use as construction materials 3.5.8 Mudrocks – check list of questions 3.6 Sandstones and related sedimentary rocks 3.6.1 Properties of the rock substances 3.6.2 Suitability for use as construction materials 3.6.3 Weathering products 3.6.4 Weathered profile and stability of slopes 3.6.5 Sandstones and similar rocks – list of questions 3.7 Carbonate rocks 3.7.1 Effects of solution 3.7.1.1 Rock masses composed of dense, fine grained rock substances comprising more than 90% of carbonate (usually Category O) 3.7.1.2 Rock masses composed of dense fine grained rock substance containing 10% to 90% of carbonate (usually Category O) 3.7.1.3 Rock masses composed of porous, low density carbonate rock substance (usually Category Y) 3.7.2 Watertightness of dam foundations 3.7.2.1 Dams which have experienced significant leakage problems 3.7.3 Potential for sinkholes to develop beneath a dam, reservoir or associated works 3.7.4 Potential for continuing dissolution of jointed carbonate rock in dam foundations 3.7.5 Potential for continuing dissolution of aggregates of carbonate rock particles and of permeable carbonate substances (Category O carbonate, in each case) 3.7.6 Discussion – potential for continuing dissolution of carbonate rocks in foundations 3.7.6.1 Category O carbonate rocks 3.7.6.2 Category Y carbonate rocks 3.7.7 Potential problems with filters’ composed of carbonate rocks 3.7.7.1 Category O carbonate rocks 3.7.7.2 Category Y carbonate materials 3.7.8 Suitability of carbonate rocks for embankment materials 3.7.9 Suitability of carbonate rocks for concrete and pavement materials 3.7.10 Stability of slopes underlain by carbonate rocks 3.7.11 Dewatering of excavations in carbonate rocks 3.7.12 Carbonate rocks – check list of questions 3.8 Evaporites 3.8.1 Performance of dams built on rocks containing evaporites 3.8.2 Guidelines for dam construction at sites which contain evaporites 3.8.3 Evaporites – checklist of questions 3.9 Alluvial soils 3.9.1 River channel deposits 3.9.2 Open-work gravels 3.9.3 Oxbow lake deposits 3.9.4 Flood plain, lacustrine and estuarine deposits 3.9.5 Use of alluvial soils for construction 3.9.6 Alluvial soils, list of questions 3.10 Colluvial soils 3.10.1 Occurrence and description 3.10.1.1 Scree and talus 3.10.1.2 Slopewash soils 3.10.1.3 Landslide debris 3.10.2 Properties of colluvial soils 3.10.2.1 Scree and talus 3.10.2.2 Slopewash 3.10.2.3 Landslide debris 3.10.3 Use as construction materials 3.10.4 Colluvial soil – list of questions 3.11 Laterites and lateritic weathering profiles 3.11.1 Composition, thicknesses and origin of lateritic weathering profiles 3.11.2 Properties of lateritic soils 3.11.3 Use of lateritic soils for construction 3.11.4 Karstic features developed in laterite terrain 3.11.5 Recognition and interpretation of silcrete layer 3.11.6 Lateritic soils and profiles – list of questions 3.12 Glacial deposits and landforms 3.12.1 Glaciated valleys 3.12.2 Materials deposited by glaciers 3.12.2.1 Properties of till materials 3.12.2.2 Disrupted bedrock surface beneath glaciers 3.12.3 Glaciofluvial deposits 3.12.4 Periglacial features 3.12.5 Glacial environment – list of questions 4 Planning, conducting and reporting of geotechnical investigations 4.1 The need to ask the right questions 4.1.1 Geotechnical engineering questions 4.1.2 Geological questions 4.1.2.1 Questions relating to rock and soil types, climate and topography 4.1.2.2 Questions relating to geological processes, i.e. to the history of development of the site 4.1.3 Geotechnical questions for investigations of existing dams 4.2 Geotechnical input at various stages of project development 4.3 An iterative approach to the investigations 4.4 Progression from regional to local studies 4.4.1 Broad regional studies 4.4.1.1 Objectives 4.4.1.2 Activities 4.4.2 Studies at intermediate and detailed scales 4.4.2.1 Objectives 4.4.2.2 Activities 4.5 Reporting 4.6 Funding of geotechnical studies 4.7 The site investigation team 5 Site investigation techniques 5.1 Topographic mapping and survey 5.2 Interpretation of satellite images aerial photographs and photographs taken during construction 5.2.1 Interpretation of satellite images 5.2.2 Interpretation of aerial photographs 5.2.2.1 Coverage 5.2.2.2 Interpretation 5.2.3 Photographs taken during construction 5.3 Geomorphological mapping 5.4 Geotechnical mapping 5.4.1 Use of existing maps and reports 5.4.2 Geotechnical mapping for the project 5.4.2.1 Regional mapping 5.4.2.2 Geotechnical mapping 5.5 Geophysical methods, surface and downhole 5.5.1 Surface geophysical methods 5.5.1.1 Seismic refraction 5.5.1.2 Self potential 5.5.1.3 Electrical resistivity 5.5.1.4 Electromagnetic conductivity 5.5.1.5 Magnetic 5.5.1.6 Microgravity 5.5.1.7 Ground penetrating radar 5.5.2 Down-hole logging of boreholes 5.5.3 Cross-hole and up-hole seismic 5.6 Test pits and trenches 5.6.1 Test pits 5.6.2 Trenches 5.7 Sluicing 5.8 Adits and shafts 5.9 Drill holes5.9.1 Drilling objectives 5.9.2 Drilling techniques and their application 5.9.3 Auger drilling 5.9.4 Percussion drilling 5.9.5 Rotary drilling 5.9.6 Sonic drilling 5.10 Sampling 5.10.1 Soil samples 5.10.2 Rock samples 5.11 In situ testing 5.11.1 In situ testing in soils 5.11.2 In situ testing of rock 5.11.2.1 Borehole orientation 5.11.2.2 Borehole impression packer 5.11.2.3 Borehole imaging 5.12 Groundwater5.13 In situ permeability tests on soil 5.14 In situ permeability tests in rock 5.14.1 Lugeon value and equivalent rock mass permeability 5.14.2 Test methods 5.14.3 Selection of test section 5.14.4 Test equipment 5.14.4.1 Packers 5.14.4.2 Water supply system 5.14.4.3 Selection of test pressures 5.14.5 Test procedure 5.14.5.1 Presentation and interpretation of results 5.15 Use of surface survey and borehole inclinometers 5.15.1 Surface survey 5.15.2 Borehole inclinometers 5.16 Common errors and deficiencies in geotechnical investigation 6 Shear strength, compressibility and permeability of embankment materials and soil foundations 6.1 Shear strength of soils6.1.1 Drained strength – definitions 6.1.2 Development of drained residual strength φR6.1.3 Undrained strength conditions 6.1.4 Laboratory testing for drained strength parameters, and common errors 6.1.4.1 Triaxial test 6.1.4.2 Direct shear test 6.1.4.3 Ring shear test 6.1.4.4 Comparison of field residual with laboratory residual strength obtained from direct shear and ring shear 6.1.5 Laboratory testing for undrained strength 6.1.6 Estimation of the undrained strength from the Over-Consolidation Ratio (OCR), at rest earth pressure coefficient Ko, and effective stress strengths 6.1.6.1 Estimation of undrained strength from OCR 6.1.6.2 Estimation of undrained strength from effective stress shear parameters 6.1.7 Estimation of the undrained strength of cohesive soils from in situ tests 6.1.7.1 Cone Penetration and Piezocone Tests 6.1.7.2 Vane shear 6.1.7.3 Self Boring Pressuremeter 6.1.8 Shear strength of fissured soils 6.1.8.1 The nature of fissuring, and how to assess the shear strength 6.1.8.2 Triaxial testing of fissured soils 6.1.9 Estimation of the effective friction angle of granular soils 6.1.9.1 Methods usually adopted 6.1.9.2 In situ tests 6.1.9.3 Laboratory tests 6.1.9.4 Empirical estimation 6.1.10 Shear strength of partially saturated soils 6.2 Shear strength of rockfill 6.3 Compressibility of soils and embankment materials 6.3.1 General principles 6.3.1.1 Within the foundation6.3.1.2 Within the embankment 6.3.2 Methods of estimating the compressibility of earthfill, filters and rockfill 6.3.2.1 Using data from the performance of other dams – earthfill 6.3.2.2 Using data from the performance of other dams – rockfill 6.3.2.3 In situ testing 6.3.2.4 Laboratory testing 6.3.2.5 Tensile properties of plastic soils 6.4 Permeability of soils 6.4.1 General principles 6.4.2 Laboratory test methods 6.4.3 Indirect test methods 6.4.3.1 Oedometer and triaxial consolidation test 6.4.3.2 Estimation of permeability of sands from particle size distribution 6.4.4 Effects of poor sampling on estimated permeability in the laboratory 6.4.5 In situ testing methods 7 Clay mineralogy, soil properties, and dispersive soils 7.1 Introduction 7.2 Clay minerals and their structure 7.2.1 Clay minerals 7.2.2 Bonding of clay minerals 7.2.2.1 Primary bonds 7.2.2.2 Secondary bonds 7.2.3 Bonding between layers of clay minerals 7.3 Interaction between water and clay minerals 7.3.1 Adsorbed water 7.3.2 Cation exchange 7.3.3 Formation of diffuse double layer 7.3.4 Mechanism of dispersion 7.4 Identification of clay minerals 7.4.1 X-ray diffraction 7.4.2 Differential Thermal Analysis (DTA) 7.4.3 Electron microscopy 7.4.4 Atterberg limits 7.4.5 The activity of the soil 7.5 Engineering properties of clay soils related to the types of clay minerals 7.5.1 Dispersivity 7.5.2 Shrink and swell characteristics 7.5.3 Shear strength 7.5.4 Erosion properties 7.6 Identification of dispersive soils 7.6.1 Laboratory tests 7.6.1.1 Emerson class number 7.6.1.2 Soil Conservation Service test 7.6.1.3 Pinhole dispersion classification 7.6.1.4 Chemical tests 7.6.1.5 Recommended approach 7.6.2 Field identification and other factors 7.7 Use of dispersive soils in embankment dams 7.7.1 Problems with dispersive soils 7.7.2 Construction with dispersive soils 7.7.2.1 Provide properly designed and constructed filters 7.7.2.2 Proper compaction of the soil 7.7.2.3 Careful detailing of pipes or conduits through the embankment 7.7.2.4 Lime or gypsum modification of the soil 7.7.2.5 Sealing of cracks in the abutment and cutoff trench 7.7.3 Turbidity of reservoir water 8 Internal erosion and piping of embankment dams and in dam foundations 8.1 The importance of internal erosion and piping to dam safety 8.2 Description of the internal erosion and piping process 8.2.1 The overall process leading to failure of a dam 8.2.2 Initiation of internal erosion 8.2.3 Continuation of erosion 8.2.4 Progression of erosion 8.2.5 Detection and intervention 8.2.6 Breach 8.3 Concentrated leak erosion 8.3.1 The overall process 8.3.2 Situations where cracking and low stress zones may be present in an embankment or the foundation 8.3.2.1 Cracking and hydraulic fracture due to cross valley differential settlement of the core 8.3.2.2 Cracking and hydraulic fracture due to cross valley arching 8.3.2.3 Cracking and hydraulic fracture due to differential settlement in the foundation under the core 8.3.2.4 Cracking and hydraulic fracture due to small scale irregularities in the foundation profile under the core 8.3.2.5 Cracking due to lack of support for the core by the shoulders of the embankment 8.3.2.6 Cracking and hydraulic fracture due to arching of the core onto the shoulders of the embankment 8.3.2.7 Crack or gap adjacent to a spillway or abutment walls and where concrete dams abut embankment dams 8.3.2.8 Crack or hydraulic fracture in poorly compacted layers in the embankment 8.3.2.9 Internal erosion associated with conduits embedded in the embankment 8.3.2.10 Cracking due to desiccation8.3.2.11 Transverse cracking caused by settlement during earthquakes 8.3.2.12 Cracking or high permeability layers due to freezing 8.3.2.13 Internal erosion initiated by the effects animal burrows and vegetation 8.3.2.14 Relative importance of conduits, spillway walls cracking mechanisms, and poorly compacted zones 8.3.3 Estimation of crack width and depth of cracking 8.3.3.1 Cracking due to differential settlement, adjacent walls 8.3.3.2 Cracks formed by collapse settlement of poorly compacted soil 8.3.4 The mechanics of erosion in concentrated leaks 8.3.4.1 The procedure for assessing whether erosion will initiate 8.3.4.2 The estimation of hydraulic shear stresses in cracks and pipes 8.3.4.3 Erosion properties of soils in the core of embankment dams – basic principles 8.3.4.4 Effect of degree of saturation of the soil 8.3.4.5 Effect of the testing method on the critical shear stress to initiate erosion (τc) and the erosion rate index 8.3.4.6 Effect of dispersion, slaking, soil structure and shear strength on erosion properties 8.3.5 Comparison of the hydraulic shear stress in the crack (τ) to the critical shear stress which will initiate erosion for the soil in the core of the embankment (τc) 8.4 Backward erosion 8.4.1 General description of backward erosion 8.4.2 Experimental modelling of backward erosion piping 8.4.3 Methods for predicting whether backward erosion piping will initiate and progress 8.4.3.1 Empirical rules for estimating a factor of safety 8.4.3.2 Terzaghi and Peck (1948) 8.4.3.3 Sellmeijer and co-workers at Deltares method 8.4.3.4 Schmertmann method 8.4.4 Some field observations 8.4.5 Suggested approach to design for and assessing backward erosion piping 8.4.6 Guidance on whether the overlying soil will form a roof to the pipe 8.4.7 Methods for prediction of initiation and progression of global backward erosion 8.5 Suffusion of internally unstable soils 8.5.1 General description of suffusion 8.5.2 Methods of identifying soils which are internally unstable and potentially subject to suffusion 8.5.2.1 General requirements 8.5.2.2 Some methods for assessing whether a soil is internally unstable 8.5.2.3 Some general comments 8.5.3 Assessment of the gradation after suffusion 8.5.4 Assessment of the seepage gradient which will cause suffusion 8.5.5 Some general comments 8.5.5.1 Need for project specific laboratory tests 8.5.5.2 Do not use “average’’ soil gradations 8.5.5.3 Allow for the effects of segregation when assessing suffusion 8.6 Contact erosion 8.6.1 General description of contact erosion 8.6.2 Methods for predicting initiation and progression of contact erosion 8.6.2.1 Non plastic sand below a coarse soil layer 8.6.2.2 Non plastic silt and clay (particles <75μm) below a coarse layer 8.6.2.3 Non-plastic silt above a coarse soil layer 8.6.2.4 General comment 8.6.3 Contact erosion or scour of the dam core into open joints in rock in the foundation 8.7 Continuation and filter action 8.8 Progression of erosion 8.8.1 General description 8.8.2 Overall approach for assessing progression for concentrated leak erosion 8.8.3 Assessing whether the soil will hold a roof to a developing pipe 8.8.4 Assessing whether crack filling action will occur 8.8.4.1 Internal erosion in the embankment 8.8.4.2 Internal erosion through the foundation 8.8.4.3 Internal erosion of the embankment into or at the foundation 8.8.5 Assessing whether upstream flow limitation will occur 8.8.6 Assessing the rate of development of the pipe 8.9 Detection of internal erosion and piping 8.9.1 General principles 8.9.2 Some information on the rate of internal erosion and piping 8.9.3 The likelihood of detection and intervention 8.10 Intervention and repair 8.11 Initiation of breach 8.11.1 General principles 8.11.2 Breach by gross enlargement 8.11.3 Breach by slope instability 8.11.4 Breach by unravelling or sloughing 8.11.5 Breach by sinkhole development leading to loss of freeboard 8.12 Assessment of the likelihood of internal erosion and piping in existing dams 8.12.1 General procedure 8.12.2 The importance of having complete and reliable information upon which to make the assessment of internal erosion 8.12.2.1 Geometric model 8.12.2.2 Geological model of the foundation 8.12.2.3 Geotechnical model of the embankment and foundations 8.12.2.4 Hydraulic or seepage model 8.12.2.5 Stress state in the dam and its foundation 8.12.2.6 General comments 8.12.3 Loading conditions 8.12.3.1 Reservoir level loading 8.12.3.2 Earthquake loading 8.12.4 Potential Failure Modes Analysis (PFMA) 8.12.5 Screening of potential failure modes 8.12.5.1 Screening of PFM on the zoning of the dam and the properties of the core of the embankment 8.12.5.2 Screening of PFM on foundation geology and properties 8.12.5.3 Screening of PFM on details of the embankment foundation geometry, compaction of the core, and conduits and retaining walls 8.12.6 Estimation of likelihoods of failure for the Potential Failure Modes applicable to the dam 8.12.6.1 Some general principles 8.12.6.2 Summary of how to estimate conditional probabilities within the event tree 8.12.6.3 Ways in which the safety of the dam against internal erosion and piping can be considered 8.12.6.4 Quantitative risk analysis methods for internal erosion and piping 9 Design, specification and construction of filters 9.1 General requirements for design and the function of filters 9.1.1 Functional requirements 9.1.2 Flow conditions acting on filters 9.1.3 Critical and non critical filters 9.1.4 Filter design notation and concepts 9.1.4.1 Notation 9.1.4.2 Filtering concepts 9.1.4.3 Laboratory test equipment 9.2 Design of critical and non-critical filters 9.2.1 Particle size based methods for designing no erosion filters with flow normal to the filter 9.2.1.1 Original USBR method 9.2.1.2 Sherard and Dunnigan method 9.2.1.3 Foster and Fell method 9.2.1.4 Vaughan and Soares method 9.2.2 Methods based on constriction or opening size 9.2.3 Methods based on the permeability of the filter 9.2.3.1 Delgardo and co-workers 9.2.3.2 Vaughan and Soares, Vaughan and Bridle method 9.2.4 Recommended method for design of critical no erosion filters, with flow normal to the filter 9.2.5 Recommended method for design of less critical and non-critical filters 9.2.5.1 Filters upstream of the dam core 9.2.5.2 Filters under rip-rap 9.2.6 Review of available methods for designing filters with flow parallel to the filter 9.2.7 Design criteria for pipe drains and pressure relief well screens 9.2.7.1 Pipe drains 9.2.7.2 Pressure relief well screens 9.2.8 Other factors affecting filter design and performance 9.2.8.1 Criteria to assess internal instability or suffusion 9.2.8.2 Segregation 9.2.8.3 Ability of the filter to hold a crack 9.2.8.4 Permeability 9.2.8.5 “Blow-out’’ or “heave’’ of the filter 9.3 Assessing filters and transition zones in existing dams 9.3.1 Some general issues and concepts 9.3.2 Continuing and excessive erosion criteria 9.3.3 Discussion of continuation scenarios in existing dams 9.3.3.1 Internal erosion in the embankment, from the embankment into the foundation or into openings in conduits passing through the embankment 9.3.3.2 Internal erosion in the foundation 9.3.3.3 Internal erosion of the embankment at or into the foundation 9.3.4 Assessment of the likelihood of continuation where a filter/transition zone does not satisfy no-erosion filter criteria 9.3.4.1 General principles 9.3.4.2 Details of how to apply the Foster and Fell (1999a, 2001) method for assessing the likelihood of continuation of erosion for filters and transitions which do not meet modern filter design criteria 9.3.5 Assessment of the likelihood of continuation for internal erosion into an open defect, joint or crack in the foundation, in a wall or conduit 9.4 Specification of particle size and durability of filters 9.4.1 Particle size distribution 9.4.2 Durability 9.4.2.1 Standard tests for durability and particle shape 9.4.2.2 Possible effects if carbonate rocks are used as filter materials 9.4.2.3 Effects if rocks containing sulphide minerals are used as filter materials 9.4.2.4 Other investigations for filter materials 9.4.3 Contractual difficulties associated with gradation and durability of filters 9.4.3.1 Fines content 9.4.3.2 Use of crushed rock for fine filters 9.5 Dimensions, placement and compaction of filters 9.5.1 Dimensions and method of placement of filters 9.5.1.1 Some general principles 9.5.1.2 Placement methods 9.5.2 Sequence of placement of filters and control of placement width and thickness 9.5.3 Compaction of filters 9.6 Use of geotextiles as filters in dams 9.6.1 Types and properties of geotextiles 9.6.2 Geotextile filter design criteria 9.6.2.1 General requirements 9.6.2.2 Filtering requirement 9.6.2.3 Clogging and blinding resistance 9.6.2.4 Permeability requirement 9.6.2.5 Durability or “survivability’’ requirement 9.6.2.6 Use of geotextile filters in dams 9.6.2.7 Construction factors 9.6.2.8 Sources of detailed information 10 Embankment dams, their zoning and design for control of seepage and internal erosion and piping 10.1 Historic performance of embankment dams and the lessons to be learned 10.2 Types of embankment dams, their advantages and limitations 10.2.1 The main types of embankment dams and zoning 10.2.2 The general principles of control of seepage pore pressures and internal erosion and piping 10.2.3 Taking account of the likelihood and consequences of failure in selecting the type of embankment 10.2.4 Types of embankment dams, their advantages, limitations and applicability 10.3 Zoning of embankment dams and typical construction materials 10.3.1 General principles 10.3.2 Examples of embankment designs 10.3.2.1 Zoned earthfill dams 10.3.2.2 Earthfill dams with horizontal and vertical drains 10.3.2.3 Central core earth and rockfill dams 10.3.2.4 Sloping upstream core earth and rockfill dam 10.3.2.5 Concrete face rockfill dams 10.4 Selection of embankment type 10.4.1 Availability of construction materials 10.4.1.1 Earthfill 10.4.1.2 Rockfill 10.4.1.3 Filters and filter drains 10.4.2 Foundation conditions 10.4.3 Climate 10.4.4 Topography and relation to other structures 10.4.5 Saddle dam 10.4.6 Staged construction 10.4.7 Time for construction 10.5 General requirements and methods of control of seepage and internal erosion and piping in embankment dams and their foundations 10.6 Some particular features of rock and soil foundations which affect seepage and internal erosion control 10.7 Details of some measures for pore pressure and seepage flow control 10.7.1 Horizontal and vertical drains in the embankment 10.7.2 Treatment of the sides of the cutoff trench 10.7.3 Prevention of critical seepage gradients and heave of the foundation 10.7.4 Design of pressure relief wells 10.8 Control of foundation seepage and internal erosion and piping by cutoffs 10.8.1 General effectiveness of cutoffs 10.8.2 Cutoff trench 10.8.3 Slurry trench cutoff backfilled with bentonite-sand-gravel 10.8.4 Grout diaphragm wall 10.8.5 Diaphragm wall using rigid or plastic concrete 10.8.6 Methods of excavation of diaphragm walls 10.8.7 Permeability and performance of cutoff walls 10.8.8 We live in a three dimensional world 10.9 Examples of dam upgrades to address deficiencies in internal erosion and piping control 10.9.1 Upgrades to reduce the likelihood of continuation of erosion by providing filters and cutoffs 10.9.2 Upgrades to reduce the likelihood of breach 11 Analysis of stability and deformations 11.1 Analysis of stability and deformations methods of analysis 11.2 Limit equilibrium analysis methods 11.2.1 General characteristics 11.2.2 Some common problems 11.2.3 Three dimensional analysis 11.2.4 Shear strength of partially saturated soils 11.3 Selection of shear strength for design 11.3.1 Drained, effective stress parameters 11.3.1.1 Peak, residual or fully softened strength in clay soils? 11.3.1.2 Selection of design parameters in clay soils 11.3.1.3 Selection of design parameters – granular soils and rockfill 11.3.2 Undrained, total stress parameters 11.3.2.1 Triaxial compression, extension or direct simple shear strength 11.3.2.2 Selection of design parameters 11.3.3 Inherent soil variability 11.4 Estimation of pore pressures and selection of strengths for steady state, construction and drawdown conditions 11.4.1 Steady state seepage condition 11.4.1.1 Steady state pore pressures 11.4.1.2 Pore pressures under flood conditions 11.4.2 Pore pressures during construction and analysis of stability at the end of construction 11.4.2.1 Some general principles 11.4.2.2 Estimation of construction pore pressures by Skempton (1954) method 11.4.2.3 Estimation of construction pore pressures from drained and specified undrained strengths 11.4.2.4 Estimation of pore pressures using advanced theory of partially saturated soil 11.4.2.5 Undrained strength analysis 11.4.2.6 Summing up 11.4.3 Drawdown pore pressures and the analysis of stability under drawdown conditions 11.4.3.1 Some general issues 11.4.3.2 Estimation of drawdown pore pressures, excluding the effects of shear-induced pore pressures 11.4.3.3 Methods for assessment of the stability under drawdown conditions 11.4.3.4 Some detailed issues for drawdown analyses 11.5 Design acceptance criteria 11.5.1 Acceptable factors of safety 11.5.2 Post failure deformation assessment 11.6 Examples of unusual issues in analysis of stability 11.6.1 Hume No. 1 Embankment 11.6.2 Eppalock Dam 11.6.3 The lessons learnt 11.7 Analysis of deformations 11.7.1 Analyses of embankment cross sections 11.7.2 Cross valley deformation analyses 11.8 Probabilistic analysis of the stability of slopes 12 Design of embankment dams to withstand earthquakes 12.1 Effect of earthquake on embankment dams 12.2 Earthquakes and their characteristics 12.2.1 Earthquake mechanisms and ground motion 12.2.2 Earthquake magnitude and intensity 12.2.3 Attenuation and amplification of ground motion 12.2.4 Earthquakes induced by the reservoir 12.3 Evaluation of seismic hazard 12.3.1 Terminology 12.3.2 General principles of seismic hazard assessment 12.3.2.1 Probabilistic approach 12.3.2.2 Seismic hazard from known active or capable faults 12.3.3 Other forms of expression of seismic hazard 12.3.4 Selection of design seismic loading 12.3.4.1 Deterministic approach 12.3.4.2 Risk based approach 12.3.4.3 Which approach to use? 12.3.5 Modelling vertical ground motions 12.3.6 The need to get good seismological advice 12.4 Principles of risk based analyses for earthquake loads 12.4.1 General principles 12.4.2 Failure by loss of freeboard and overtopping 12.4.3 Failure by cracking and internal erosion and piping 12.5 Liquefaction of dam embankments and foundations 12.5.1 Definitions and the mechanics of liquefaction 12.5.1.1 Definitions 12.5.1.2 Some consideration of the mechanics of liquefaction of granular soils 12.5.1.3 Suggested flow chart for evaluation of soil liquefaction 12.5.2 Soils susceptible to liquefaction 12.5.2.1 Methods based on soil classification and in situ moisture content 12.5.2.2 Discussion and recommended approach 12.5.2.3 Methods based on geology and age of the deposit 12.5.3 The “simplified procedure’’ for assessing liquefaction resistance of a soil 12.5.3.1 Background to the simplified method 12.5.3.2 Discussion of differences between the Youd et al. (2001), Seed et al. (2003) and Idriss and Boulanger (2008) methods 12.5.3.3 The simplified method – outline 12.5.3.4 Evaluation of Cyclic Stress Ratio (CSR) 12.5.3.5 Evaluation of Cyclic Resistance Ratio for M7.5 earthquakes (CRR7.5) from the Standard Penetration Tests using the Boulanger and Idriss (2012), Idriss and Boulanger (2008) method 12.5.3.6 Evaluation of the Cyclic Resistance Ratio for M7.5 earthquake (CRR7.5) from Cone Penetration Tests using the Idriss and Boulanger (2008) method 12.5.3.7 Evaluation of Cyclic Resistance Ratio for M7.5 earthquake (CRR7.5) from shear wave velocity using the Andrus and Stokoe (2000) method 12.5.3.8 Earthquake magnitude scaling factors and factor of safety against liquefaction 12.5.3.9 Corrections for overburden stress and static shear stress 12.5.3.10 Allowance for the age of the soil deposit 12.6 Liquefied undrained shear strength and post earthquake stability analysis 12.6.1 Some general principles 12.6.2 Background to the assessment of the liquefied shear strength Su(LIQ) 12.6.3 Some methods for assessing the strength of liquefied soils in the embankment and foundation 12.6.3.1 “Critical State’’ based methods 12.6.3.2 Normalized strength ratio methods 12.6.3.3 Other methods 12.6.4 Some other factors to consider 12.6.5 Recommended approach to assessing the liquefied undrained strength soils of in the embankment and foundation 12.6.6 Methods for assessing the post earthquake strength of non-liquefied soils in the embankment and foundation 12.6.6.1 Saturated potentially liquefiable soils 12.6.6.2 Cyclic softening in clays and plastic silts 12.6.6.3 Compacted plastic and non-plastic soils 12.6.7 Liquefaction potential and limit equilibrium stability analysis 12.6.8 Site investigations requirements and development of geotechnical model of the foundation 12.7 Seismic deformation analysis of embankment dams 12.7.1 Preamble 12.7.2 Performance of embankment dams during earthquakes 12.7.3 The methods available and when to use them 12.7.4 Suggested approach to estimation of deformations 12.7.5 Screening methods 12.7.5.1 USACE method 12.7.5.2 Hynes-Griffin and Franklin (1984) pseudo-static seismic coefficient method 12.7.6 Empirical database methods 12.7.6.1 Swaisgood (1998, 2003) empirical method for estimating crest settlements 12.7.6.2 Pells and Fell empirical method for estimating settlement, damage and cracking 12.7.7 Simplified methods of deformation analysis for dams where liquefaction and significant strain weakening do not occur 12.7.7.1 General principles 12.7.7.2 Makdisi and Seed (1978) method 12.7.7.3 Bray and Travasarou (2007) method 12.7.8 Advanced numerical methods for estimating deformations during and post earthquake for non-liquefied and liquefied conditions 12.7.8.1 Total stress codes 12.7.8.2 Effective stress codes 12.7.8.3 Summary 12.8 Defensive design principles for embankment dams 12.9 Methods for upgrading embankment dams for seismic loads 12.9.1 General approaches 12.9.2 Upgrading of embankment dams not subject to liquefaction 12.9.3 Embankment dams subject to liquefaction 13 Embankment dam details 13.1 Freeboard 13.1.1 Definitions and overall requirements 13.1.2 Examples of freeboard requirements 13.1.2.1 New embankment dams 13.1.2.2 Existing embankment dams 13.1.2.3 Suggested approach for determining freeboard 13.1.3 Estimation of wave run up freeboard for design of small dams and for feasibility and preliminary design 13.1.4 Estimation of wind setup and wave run-up for detailed design 13.1.4.1 Fetch 13.1.4.2 Design wind 13.1.4.3 Wave height 13.1.4.4 Wave length and wave period 13.1.4.5 Wave run-up 13.1.4.6 Wind set-up 13.2 Slope protection 13.2.1 Upstream slope protection 13.2.1.1 General requirements 13.2.1.2 Sizing and layer thickness 13.2.1.3 Selection of design wind speed and acceptable damage 13.2.1.4 Rock quality and quarrying 13.2.1.5 Design of filters under rip-rap 13.2.1.6 Use of soil cement and shotcrete for upstream slope protection 13.2.2 Downstream slope protection 13.2.2.1 General requirements 13.2.2.2 Grass and rockfill cover 13.3 Embankment crest details 13.3.1 Camber 13.3.2 Crest width 13.3.3 Curvature of crest in plan 13.4 Embankment dimensioning and tolerances 13.4.1 Dimensioning 13.4.2 Tolerances 13.5 Conduits through embankments 13.5.1 Piping into the conduit 13.5.2 Piping along and above the conduit 13.5.3 Flow out of the conduit 13.5.4 Conclusions 13.5.5 Recommendations 13.6 Interface between earthfill and concrete structures 13.6.1 Interface between retaining walls and embankment 13.6.2 Interface between concrete gravity dam and embankment 13.7 Flood control structures 13.8 Design of dams for overtopping during construction 13.8.1 General design concepts 13.8.2 Types of steel mesh reinforcement 13.8.3 Design of steel reinforcement 13.9 Design of rip rap for minor overtopping of levees or small dams during floods 13.10 Other overtopping protection methods for embankment dams 14 Specification and quality control of earthfill and rockfill 14.1 Specification of rockfill 14.2 Specification of earthfill 14.3 Specification of filters 14.4 Quality control 14.4.1 General 14.4.2 ‘Methods,’ and ‘performance’ criteria 14.4.3 Quality control 14.4.4 Influence of non technical factors on the quality of embankment dams 14.5 Testing of rockfill 14.5.1 Particle size, density and permeability 14.5.2 Field rolling trials 14.6 Testing of earthfill 14.6.1 Compaction-test methods 14.6.2 Compaction control – some common problems 14.6.3 Compaction control – some other methods 15 Concrete face rockfill dams 15.1 General arrangement and reasons for selecting this type of dam 15.1.1 Historic development of concrete face rockfill dams 15.1.2 General arrangement – modern practice 15.1.3 Site suitability, and advantages of concrete face rockfill dams 15.2 Rockfill zones and their properties 15.2.1 Zone 2D – Transition rockfill 15.2.2 Zones 2E, 3A and 3B – Fine rockfill, rockfill and coarse rockfill 15.2.2.1 General requirements 15.2.2.2 Layer thickness and compaction 15.2.2.3 Use of gravel as rockfill 15.2.3 Effect of rock properties, compaction and addition of water during compaction on modulus of rockfill 15.2.4 Estimation of the modulus of rockfill 15.2.4.1 Estimation of the secant modulus Erc 15.2.4.2 Estimation of the first filling ‘pseudo modulus’ Erf 15.2.4.3 Effect of valley shape 15.2.5 Selection of side slopes and analysis of slope stability 15.3 Concrete face 15.3.1 Plinth 15.3.2 Face slab 15.3.2.1 Face slab thickness 15.3.2.2 Reinforcement 15.3.2.3 Vertical and horizontal joints 15.3.3 Perimetric joint 15.3.3.1 General requirements15.3.3.2 Water stop details 15.3.4 Crest detail 15.4 Construction aspects 15.4.1 Plinth construction and special details 15.4.2 River diversion 15.4.3 Embankment construction 15.5 Some non-standard design features 15.5.1 Use of dirty rockfill 15.5.2 Dams on erodible foundation 15.5.3 Leaving alluvium in the dam foundation 15.5.4 Plinth gallery 15.5.5 Earthfill cover over the face slab 15.5.6 Spillway over the dam crest 15.6 Observed settlements, and displacements of the face slab, and joints 15.6.1 General behaviour 15.6.2 Post construction crest settlement 15.6.3 Face slab displacements and cracking 15.6.4 Cracks in CFRD dams 15.7 Observed leakage of CFRD 15.7.1 Modern CFRD 15.7.2 Early CFRD and other dams which experienced large leakage 15.8 Framework for assessing the likelihood of failure of CFRD 15.8.1 Overview of approach 15.8.2 Assessment of likelihood of initiation of a concentrated leak 15.8.3 Assessment of the likelihood of continuation of a concentrated leak 15.8.4 Assessment of the likelihood of progression to form a pipe 15.8.5 Assessment of the likelihood of a breach forming 15.8.6 Concluding remarks 15.9 Further reading 16 Concrete gravity dams and their foundations 16.1 Outline of this chapter 16.2 Analysis of the stability for normal operating and flood loads 16.2.1 Design loads 16.2.2 Load combinations 16.2.3 Kinematically feasible failure models 16.2.4 Analysis of stability 16.2.5 Acceptance criteria 16.3 Strength and compressibility of rock foundations 16.3.1 Some general principles 16.3.2 Assessment of rock shear strength 16.3.2.1 General requirements 16.3.2.2 Shear strength of clean discontinuities 16.3.2.3 Shear strength of infilled joints and seams showing evidence of previous displacement 16.3.2.4 Shear strength of thick infilled joints, seams or extremely weathered beds with no previous displacement 16.3.2.5 Shear strength of jointed rock masses with no persistent discontinuities 16.3.3 Tensile strength of rock foundations 16.3.4 Compressibility of jointed rock foundation 16.3.5 Ultimate bearing capacity of rock foundations 16.4 Strength of the concrete in the dam 16.4.1 What is recommended in guidelines 16.4.2 Measured concrete strengths from some USA dams 16.4.2.1 Background to the data 16.4.2.2 Tensile strength of concrete and lift joints 16.4.2.3 Shear strength of concrete 16.5 Strength of the concrete – rock contact 16.6 Uplift in the dam foundation and within the dam 16.6.1 What is recommended in guidelines? 16.6.2 Some additional information on uplift pressures 16.6.2.1 Effects of geological features and deformations on foundation uplift pressures 16.6.2.2 Analysis of EPRI (1992) uplift data 16.6.2.3 Design of drains 16.6.2.4 Hydro-dynamic forces 16.6.2.5 Aprons 16.6.2.6 ‘Contact’ or ‘box’ drains 16.7 Silt load 16.8 Ice load 16.9 The design and analysis of gravity dams for earthquake loading 16.9.1 Introduction 16.9.2 Gravity dams on soil foundations 16.9.3 Gravity dams on rock foundations 16.9.3.1 General 16.9.3.2 The Westergaard pseudo-static method 16.9.3.3 The Fenves-Chopra refined pseudo-static method 16.9.3.4 The US Corps of engineers method 16.9.3.5 Finite Element Method (FEM) 16.9.3.6 Design earthquake input motion 16.9.3.7 Should vertical ground motion be included? 16.9.3.8 Reservoir level variation 16.9.3.9 What do the results of analyses mean? 16.9.3.10 Post-earthquake analyses 16.9.3.11 Dams on rock foundations with potentially deep-seated failure mechanisms 16.9.3.12 Dams on foundations that could be subjected to ground displacement 16.9.4 Concluding remarks 17 Foundation preparation and cleanup for embankment and concrete dams 17.1 General requirements 17.1.1 Embankment dams 17.1.2 Concrete dams 17.1.3 Definition of foundation requirements in geotechnical terms 17.2 General foundation preparation for embankment dams 17.2.1 General foundation under earthfill 17.2.1.1 Rock foundation 17.2.1.2 Soil foundation 17.2.2 General foundation under rockfill 17.2.3 General foundation under horizontal filter drains 17.3 Cutoff foundation for embankment dams 17.3.1 The overall objectives 17.3.2 Cutoff in rock 17.3.3 Cutoff in soil 17.4 Width and batter slopes for cutoff in embankment dams 17.4.1 Cutoff width W 17.4.2 Batter slope 17.4.3 Setting out 17.5 Selection of cutoff foundation criteria for embankment dams 17.6 Slope modification and seam treatment for embankment dams 17.6.1 Slope modification 17.6.2 Seam treatment 17.6.3 Dental concrete, pneumatically applied mortar, and slush concrete 17.6.4 The need for good records of foundation treatment 17.7 Assessment of existing embankment dams 17.8 Foundation preparation for concrete gravity dams on rock foundations 17.8.1 The general requirements 17.8.2 Excavation to expose a suitable rock foundation 17.8.3 Treatment of particular features 17.8.4 Treatment at sites formed by highly stressed rock 18 Foundation grouting 18.1 General concepts of grouting dam foundations 18.2 Grouting design – cement grout 18.2.1 Staging of grouting 18.2.2 The principles of ‘closure’ 18.2.3 The design and quality control of cement grouts 18.2.3.1 The cement and additives used for grouting 18.2.3.2 Water cement ratio 18.2.3.3 Rheological properties of grout 18.2.3.4 High, medium and low mobility grouts 18.2.3.5 Field quality control testing of grouts 18.2.3.6 Grout pressure 18.2.3.7 Recommended closure criteria for embankment and concrete dams18.2.4 Effect of cement particle size, viscosity, fracture spacing and Lugeon value on the effectiveness of grouting 18.2.5 The effectiveness of a grout curtain in reducing seepage 18.2.6 The depth and lateral extent of grouting 18.2.7 Grout hole position and orientation 118.3 Some practical aspects of grouting with cement 18.3.1 Grout holes 18.3.2 Standpipes 18.3.3 Grout caps 18.3.4 Grout mixers, agitator pumps and other equipment 18.3.5 Monitoring of grouting program 18.3.6 Water pressure testing 18.4 Prediction of grout takes 18.5 Durability of cement grout curtains 18.6 Chemical grouts in dam engineering 18.6.1 Types of chemical grouts and their properties18.6.2 Grout penetrability in soil and rock 18.6.3 Grouting technique 18.6.4 Applications to dam engineering 19 Mine and industrial tailings dams 19.1 General 19.2 Tailings and their properties 19.2.1 What are mine tailings? 19.2.2 Tailings terminology and definitions 19.2.3 Tailings properties 19.2.3.1 General 19.2.3.2 Particle size 19.2.3.3 Mineralogy 19.2.3.4 Dry density and void ratio 19.2.3.5 Permeability 19.2.3.6 Properties of water in tailings 19.3 Methods of tailings discharge and water recovery 19.3.1 Tailings discharge 19.3.2 Cyclones 19.3.3 Sub-aqueous vs sub-aerial deposition 19.3.4 Water Recovery 19.4 Prediction of tailings properties 19.4.1 Beach slopes and slopes below water 19.4.2 Particle sorting 19.4.3 Permeability 19.4.4 Dry density 19.4.5 The prediction of desiccation rates 19.4.6 Drained and undrained shear strength 119.4.6.1 Drained shear strength 19.4.6.2 Undrained shear strength 19.5 Methods of construction of tailings dams 19.5.1 General 19.5.2 Construction using tailings 19.5.2.1 Upstream method 19.5.2.2 Downstream method 19.5.2.3 Centreline method19.5.3 Construction using conventional water dams19.5.4 Selection of embankment construction method 19.5.5 Control of seepage by tailings placement, blanket drains and under-drains 19.5.5.1 Tailings placement 19.5.5.2 Drainage blankets and under-drains 19.5.6 Some factors affecting the potential for internal erosion and piping of tailings dams 19.5.7 Some factors to consider for seismic design of tailings dams 19.5.7.1 Conventional dams and downstream construction 19.5.7.2 Upstream construction 19.5.8 Storage layout 19.5.9 Other disposal methods 19.5.9.1 Thickened discharge or Robinsky method 19.5.9.2 Co-disposal 19.5.9.3 Paste disposal 19.5.9.4 Belt filtration19.5.9.5 Disposal into open cut and underground mine workings 19.5.9.6 Discharge into rivers or the sea 19.6 Seepage from tailings dams and its control 19.6.1 General 19.6.2 Principles of seepage flow and estimation 19.6.3 Some common errors in seepage analysis 19.6.4 Seepage control measures 19.6.4.1 Controlled placement of tailings 19.6.4.2 Foundation grouting 19.6.4.3 Foundation cutoffs 19.6.4.4 Clay liners 19.6.4.5 Under-drains 19.6.4.6 Synthetic liners (geomembranes) 19.6.4.7 Geomembrane liners 19.6.5 Seepage collection and dilution measures 19.6.5.1 Toe drains 19.6.5.2 Pump wells 19.6.5.3 Seepage collection and dilution dams 19.6.6 Rehabilitation 19.6.6.1 Long term stability and settlement 19.6.6.2 Erosion control 19.6.6.3 Seepage control 19.6.6.4 Return of area to productive use 20 Monitoring and surveillance of embankment dams 20.1 What is monitoring and surveillance? 20.2 Why undertake monitoring and surveillance? 20.2.1 The objectives 20.2.2 Is it really necessary? 20.2.3 Some additional information on embankment dam failures and incidents 20.2.4 Time for development of internal erosion and piping failure of embankment dams and ease of detection 20.2.5 The ability of monitoring to detect slope instability 20.3 What inspections and monitoring is required? 20.3.1 General principles 20.3.2 Some examples of well instrumented embankment dams 20.3.3 Dam safety inspections 20.4 How is the monitoring done? 20.4.1 General principles 20.4.2 Seepage flow measurement and observation 20.4.3 Surface displacements 20.4.4 Pore pressures 20.4.4.1 Why and where are pore pressures measured? 20.4.5 Pore air and pore water pressure 20.4.5.1 Fluctuations of pore pressure with time and the lag in response of instruments 20.4.5.2 Types of instruments and their characteristics 20.4.6 Should piezometers be installed in the cores of earth and earth and rockfill dams? 20.4.7 Displacements and deformation 20.4.7.1 Vertical displacements and deformation 20.4.7.2 Horizontal displacements and deformations 20.4.8 Thermal monitoring of seepage 20.4.8.1 General 20.4.8.2 Distributed fibre optic temperature sensing 20.4.8.3 Thermotic sensors in stand pipes in the dam 20.4.8.4 Infra-red imaging of the downstream face of the dam and foundations 20.4.9 Use of geophysical methods to detect seepage 20.4.9.1 Self potential 20.4.9.2 Resistivity 20.4.9.3 Other methods ReferencesAppendix A: Methods for estimating the probability of failure by internal erosion and piping Subject index