SMALL DAMS PETITS BARRAGES

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APPENDIX - RECOMMENDED EMBANKMENT SLOPES FOR EARTHFILL <strong>DAMS</strong> 1. Experience of China In China the completed earth dams are mainly of rolled-fill type, and comprise up to date over 95% of the entire large dams. There are many causes of slope failure. The major ones are the improper control of the placement water content, the low dry density and the low shearing strength. Practice has shown that for a homogeneous dam of poor placement quality, sudden drawdown of reservoir level from full height to one third of the full height may easily cause sliding of the upstream slope, and that the high position of phreatic line during the first filling of the reservoir or the saturation of the embankment by submergence after continual raining may also lead to sliding of the downstream slope. In some cases, the dam slopes during construction or reservoir drawdown often slid along the weak layers interbedded in the foundation. In the Hubei Province, the dam slopes are specified within the limit as shown in Table 5.21. This method provides convenience for the masses and also ensures the dam safety. Homogeneos Dams Sloping-core Earth Dams Earth dams with central core Table 5.21 – Range of embankment slopes for dams below 15 m.[1] Sand Clay Silty loam Widt h of berms (m) Berm Nº of Berms 1.5 1 Widt h of berms (m) Berm Nº of Berms 1.5 1 Widt h of berms (m) Berm Nº of Berms 1.5 1 Upstream slope (from top to bottom) Downstrea m slope (from top to bottom) Width of berms (m) Berm Nº of Berms Upstrea m slope (from top to bottom) Downstrea m slope (from top to bottom) 1:2.5 1:2.25 1:2.25 1:2.0 1:2.75 1:2.5 1:2.5 1:2.25 Embankment Sloping-core and cutoff trench Upstream slope (from top to bottom) 1:2.50 1:2.75 Downstrea m slope (from top to bottom) 1:2.0 1:2.25 Top thickness (normal to dam slope) 0.8 m Bottom thickness (normal to dam slope) ¼ of dam height Bottom width of foundation cutoff trench ¼ of dam height Dam Shell Central core and cutoff trench Upstream slope (from top to bottom) 1:2~1:2.25 1:2.25~1:2.5 0 2. Experience of United States •Homogeneous Dam Downstrea m slope (from top to bottom) 1:1.75~1:2. 0 1:2~1:2.25 Top width Slope 1.5 1:0.2 Bottom width of foundation cutoff trench ¼ water head Bottom width of abutment cutoff trench ¼ of dam height Bottom width of abutment cutoff trench ½ water head 86
The homogeneous dam is recommended only where the lack of free-draining materials make the construction of a zoned embankment uneconomical, with the further qualification that for storage dams the homogeneous dam must be modified to include internal drainage facilities. Even in the construction of a homogeneous embankment, there is likely to be some variation in the nature of borrow material. It is important that the coarse and more pervious material be placed at the outer slopes to approach, as much as possible, the advantages of zoned embankment. It is also important to avoid segregation of the larger particles when the fill is dumped. Segregation leads to the formation of layers of much greater permeability than the other embankment; these layers tend to form drainage channels for percolating water and to increase the possibility of piping. Because of the possibility of oversights during construction and of cracking, dispersive soil, etc., as discussed previously, consideration should be given to providing an inclined filterdrain to intercept any seepage along defects in the embankment. The recommended slopes for small homogeneous earthfill dams are shown in Table 6 for detention and storage dams on stable foundations with and without rapid drawdown as a design condition. Where more than one soil classification is shown for a set of slopes, the table indicates that the dam can be constructed to the slopes shown by using any of the soil or combinations thereof. Zoned embankments The zoned embankment dam consists of a central impervious core flanked by zones of material that are considerably more pervious. The recommended slopes for small zoned embankment dams are shown in Table 5.23. An excellent example of a zoned dam from the 1950 era is Carter Lake Dam. An excellent example of a more recent era is Ute Dam Dike. This type of embankment should always be constructed where there is a variety of soils readily available because its inherent advantages lead to savings in the costs of construction. Three major advantages in using zoned embankments are listed below: � Steeper slopes may be used with consequent reduction in total volume of embankment materials; � A wide variety of materials may be used; � Maximum use can be made of material excavated from the foundation, spillway, outlet works, and other appurtenant structures. 87
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SMALL DAMS Design, Surveillance and
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FOREWORD The ICOLD - International
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ACKNOWLEDGEMENT The Ad Hoc Committe
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FOREWORD ACKNOWLEDGEMENT SUMMARY TA
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5.5.5 Compaction in confined areas
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7.2.1 Introduction 7.2.2 Spillway c
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1. SMALL DAMS DEFINITION AND CLASSI
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2 Fig. 1.2 - Relationship H . V wit
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1.3 REFERENCES [1] French Committe
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2.3 ZONED EARTHFILL DAMS In arid pa
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sloping core guarantees water impou
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Fig. 2.11 - Hlinky Concrete Gravity
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Fig. 2.13 - Photograph of Neusberg
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The gabion dam as the gabion retain
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Some inflatable dams are operated b
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3.1 INTRODUCTION 3. SAFETY OF SMALL
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Condition Effect on safety 13. Dama
Page 35 and 36: Fig. 3.2 - Massive dam break overto
Page 37 and 38: and suffusion or internal instabili
Page 39 and 40: downstream part of the embankment m
Page 41 and 42: small dam impounding a lot of water
Page 43 and 44: Whenever the Supervising Authority
Page 45 and 46: emergency management organizations
Page 47 and 48: c) The decommissioning plan should
Page 49 and 50: 5.1 INTRODUCTION 5. FEATURES OF THE
Page 51 and 52: 5.2 DESIGN FLOODS Inadequate flood
Page 53 and 54: downstream slope will show seepage
Page 55 and 56: Fig. 5.2 - Design Freeboard 5.4.3 F
Page 57 and 58: 2 U f Fe S 1400 D Where Uf is the d
Page 59 and 60: Maximum compaction is obtained at c
Page 61 and 62: characteristic must be determined.
Page 63 and 64: 5.6.1 Foundation Watertightness The
Page 65 and 66: � A continuous vertical chimney d
Page 67 and 68: Thickness of pervious layer Thick D
Page 69 and 70: t 5.7.1.4 Practical Considerations
Page 71 and 72: It is generally accepted that cohes
Page 73 and 74: � Simple Bishop (1955) � Spence
Page 75 and 76: � The elements for surface draina
Page 77 and 78: The supporting layer for the rip-ra
Page 79 and 80: For very small reservoirs (fetch of
Page 81 and 82: The junction of the downstream slop
Page 83 and 84: Fig. 5.14 - Hongshiyan homogenous d
Page 85: material has been left in place or
Page 89 and 90: [3] OL and OH soils are not recomme
Page 91 and 92: part (core) lies in the zone (Fig.
Page 93 and 94: 6. GUIDELINES ON SURVEILLANCE OF SM
Page 95 and 96: cases the owner may retain the serv
Page 97 and 98: Surface displacement on an embankme
Page 99 and 100: Fig. 6.1 - Leakage measurement usin
Page 101 and 102: Water Level Sounder - Details of th
Page 103 and 104: pressure) Left abutment 2 5 Weir ga
Page 105 and 106: Fig. 6.9 - Recommended standpipe pi
Page 107 and 108: the others weir gauges need to be i
Page 109 and 110: � Earthquakes sensible at the dam
Page 111 and 112: APPENDIX INSPECTION CHECKLIST FOR S
Page 113 and 114: Exposed reinforcement � The condu
Page 115 and 116: These spillways can be lined or unl
Page 117 and 118: flowing water. Flowing water with h
Page 119 and 120: Fig. 7.3 - Installation of the arti
Page 121 and 122: Fig. 7.7 - Dam overtopping protecti
Page 123 and 124: complete construction was in 2001,
Page 125 and 126: In some cases, the downstream face
Page 127 and 128: Tube-a-manchettes injection system
Page 129 and 130: 7.3.5 Slope Protection Measures 7.3
Page 131 and 132: Pipe Rehabilitation SLIPLINING MODI
Page 133 and 134: Conditions Pros Cons Comments types
Page 135 and 136: Embankment dams that have properly
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and minimize erosion. Design of sui
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[20] SMEC- “Draft Guidelines for
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present visual information. It must
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Fig. 8.1 - Three small dams in casc
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Social Disruption low (rural area)
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Fig. 8.4 - Flood water level after
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8.9 REFERENCES [1] BURREC (1994) -
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SMALL DAMS PETITS BARRAGES

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