SMALL DAMS PETITS BARRAGES

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Kind of reinforcement of the dam slope Coarse surface (stone packing, armouring, vegetation cover) Smooth surface (asphalt-concrete, concrete, pavement) 5.4.5 Camber Table 5.6 – Height of wind waves Camber (overbuild) of the crests of embankment dams is generally provided, in addition to conventional freeboard allowances, to accommodate anticipated post-construction settlements. Federal guidelines in the U.S. also recommend increasing freeboard in areas that have high seismic activity to accommodate the possibility of permanent embankment displacements and/or reservoir seiches during large earthquakes (ICODS, 1998). If the reservoir rim is unstable, additional freeboard may also be provided for the possibility of landslide-generated water waves and/or displacement of reservoir volume. 5.5 SOIL COMPACTION Compaction is the most important factor in achieving a stable, durable and solid earth embankment, which is resistant to the constant seepage of water through the soil as well as having stable slopes. It is important to point out that many dams failed because of poor compaction. Compaction occurs when pressure is applied to the soil so that the individual soil grains are pushed together as air is expelled. Compaction in the field is directed at reducing the percentage voids to less than 5%. Compaction of soil to a certain standard (i.e. density and water content) not only prevents excessive leakage and failure but also provides the basis for the determination of other properties e.g. strength, permeability, settlement and elasticity. By applying compaction to a specific standard a norm is set against which the properties are known and the behaviour and safety of an embankment can be forecasted. Stress/strain deformation characteristics of embankments are also important. Embankments should under no condition develop low compressive stresses and excessive shear forces as this can lead to failure. 5.5.1 Compaction Standards Effective length of wave run-up in meters Height of the wave run-up in m For a design speed 72 km.h-1 1 : 3 1 : 2 100 0.33 0.42 200 0.43 0.54 300 0.50 0.64 100 0.42 0.53 200 0.54 0.67 300 0.62 0.80 Regardless of the type of compacting equipment or the degree of cohesion of the soil, the effectiveness of the compaction procedure depends to a large extent on the moisture content of the soil. This statement applies especially to almost nonplastic uniform fine-grained soils. 58
Maximum compaction is obtained at certain water content for a specific energy application. In the Fig. 5.3 is presented the relation between dry density and placement moisture content for a particular soil under a specific compaction procedure for a given compaction equipment. Fig.5.4 – Usual relation between dry density and optimum water content for a specific compaction energy. When the soil is compacted by the same method but using different compaction equipment (different energy), it is obtained a family of similar curves, as illustrated in Fig. 5.4. Fig.5.5 – Typical moisture-density curves for the same soils but with different compaction energy. With reasonable care it is usually possible to maintain the water content at +/- 2 % of optimum, which is the usual standard. 59
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SMALL DAMS Design, Surveillance and
Page 3 and 4:
FOREWORD The ICOLD - International
Page 5 and 6:
ACKNOWLEDGEMENT The Ad Hoc Committe
Page 7 and 8: FOREWORD ACKNOWLEDGEMENT SUMMARY TA
Page 9 and 10: 5.5.5 Compaction in confined areas
Page 11 and 12: 7.2.1 Introduction 7.2.2 Spillway c
Page 13 and 14: 1. SMALL DAMS DEFINITION AND CLASSI
Page 15 and 16: 2 Fig. 1.2 - Relationship H . V wit
Page 17 and 18: 1.3 REFERENCES [1] French Committe
Page 19 and 20: 2.3 ZONED EARTHFILL DAMS In arid pa
Page 21 and 22: sloping core guarantees water impou
Page 23 and 24: Fig. 2.11 - Hlinky Concrete Gravity
Page 25 and 26: Fig. 2.13 - Photograph of Neusberg
Page 27 and 28: The gabion dam as the gabion retain
Page 29 and 30: Some inflatable dams are operated b
Page 31 and 32: 3.1 INTRODUCTION 3. SAFETY OF SMALL
Page 33 and 34: 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: 2 U f Fe S 1400 D Where Uf is the d
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 and 86: material has been left in place or
Page 87 and 88: The homogeneous dam is recommended
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
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� Earthquakes sensible at the dam
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APPENDIX INSPECTION CHECKLIST FOR S
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Exposed reinforcement � The condu
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These spillways can be lined or unl
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flowing water. Flowing water with h
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Fig. 7.3 - Installation of the arti
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Fig. 7.7 - Dam overtopping protecti
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complete construction was in 2001,
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In some cases, the downstream face
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Tube-a-manchettes injection system
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7.3.5 Slope Protection Measures 7.3
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Pipe Rehabilitation SLIPLINING MODI
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Conditions Pros Cons Comments types
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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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