SMALL DAMS

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Chapter III The section Geotechnical studies in Chapter IV, p. 68 emphasises the advantages of a simple test (water content) and explains what practical conclusions should be drawn from the results of those various tests. Rockfill For aggregate and rockfill, the laboratory tests required are: !" measurement of intrinsic characteristics: apparent density, mineralogical study (examination of thin slices under a microscope); !" measurement of state characteristics: water content, grain size range and block size range, shape coefficients, porosity, degree of cracking, continuity index; !" measurement of withstand characteristics: impact (Los Angeles or LA test), abrasion (Micro-Deval test with water), compressive strength Rc (on cylindrical core samples), freeze thaw cycles. SITE TESTS AND MEASUREMENTS Several types of tests and measurements can be done in situ at various stages of study on a dam site according to a variety of criteria (nature of the foundation, geotechnical problems, dam size, etc.). They can be used to roughly measure the foundation's mechanical characteristics, incorporating the effect of discontinuities in the rock mass. The tests done will depend on the nature of the foundation. In loose overburden, we can cite: !"static or dynamic penetrometer tests, which in particular distinguish between layers of different consistence without offering the possibility of directly and reliably linking peak resistance to their mechanical characteristics; !"pressure meter tests to obtain a stress-strain relation in the ground (e.g. determination of a strain modulus, creep pressure and limit pressure); !"shear vane apparatus to measure the undrained cohesion of the ground when it is less than 0.1 MPa. It is not possible to measure the cohesion of layers whose thickness is less than the height of the vane apparatus blades; !"phicometer to give an approximate direct measurement in the drillhole of the shear strength of heterogeneous or coarse soils. These various in situ tests are less rarely used to study a dam than for other constructions except when the foundation is of very mediocre quality, for example mud. On rocky terrains, the classic tests are as follows, the first two concerning the foundation, and the second two knowledge of materials: !"dilatometer deformability test in the drillhole, plate bearing or flat-jack test to measure the strain modulus of the rock in various directions (these tests are difficult to do, require highly qualified labour and are very expensive, which generally restricts their use to the largest structures); 47
G eological and geotechnical studies !" measurement of seismic velocities in the foundation rock, which gives a global value for the quality of that rock; !" rockfill blasting tests using various blasting systems and charges should be done, with a determination of the characteristics of the resulting rockfill (block size distribution, shapes, amount of tailings, etc.); !" full size rockfill compaction test embankments. RECOMMENDATIONS FOR CONDUCT OF THE STUDIES 48 The sequencing suggested hereafter is obviously subjective. It corresponds to routine practice for dams of a certain size but obviously it would be possible to envisage a different breakdown of the geological and geotechnical studies, in particular for small dams (with the phases simplified and combined), or according to the specific features of the site whether they are technical or not (for example land ownership problems may cause difficulties in access and can speed up or delay some site investigations). Similarly, the naming of these phases is not standardised, and practice varies considerably from one project to another. Outside questions of terminology, the important point is that the content of the studies corresponds to the stages that must be gone through in succession when a dam project is set up and carried out. SITE IDENTIFICATION AND SELECTION Objective If possible, the ideal situation is a location near the needs to be met, permitting storage of the required volume of water (in relation with the results of the hydrological study, i.e. filling by natural or mechanical means), with a geometrically optimal structure (ratio of the volume stored to the volume of the dam, which is directly related to its cost). In the case of a reservoir for recreational purposes, the surface area of the lake will be more important. Methodology Systematic inventory of potential dam sites is generally carried out over a certain area and according to criteria that are related to the nature of the needs to be met. Projects can be sorted in a preliminary manner in this stage according to various considerations (suitability to the size of the catchment area and therefore natural inflow to meet storage requirements; land use constraints such as flooding of inhabited areas, roads or other networks, etc.; potential of the site's geometry; proximity to needs; and so on).
Page 1 and 2: FRENCH COMMITTEE ON LARGE DAMS COMI
Page 3 and 4: PHOTOGRAPH REFERENCES Cover: CACG,
Page 5 and 6: M E M B E R S O F T H E R E A D I N
Page 7 and 8: TABLE OF CONTENTS Foreword - What n
Page 9 and 10: Table of contents FILL DAM DESIGN..
Page 11 and 12: Table of contents Chap. VII - Life
Page 13 and 14: W hat need for guidelines for small
Page 15 and 16: W hat need for guidelines for small
Page 17 and 18: C hoice of site and type of dam TOP
Page 19 and 20: C hoice of site and type of dam AVA
Page 21 and 22: C hoice of site and type of dam CON
Page 23 and 24: P reliminary determination of desig
Page 37 and 38: G eological and geotechnical studie
Page 45: G eological and geotechnical studie
Page 67 and 68: F ill dams GEOTECHNICAL STUDIES 68
Page 69 and 70: F ill dams For fill, the wetter the
Page 71 and 72: F ill dams 72 If the latter is unal
Page 73 and 74: F ill dams As concerns freeboard R,
Page 75 and 76: F ill dams Wave height h (m) Thickn
Page 77 and 78: F ill dams In the case of a widely
Page 79 and 80: F ill dams Fig. 3 - Sloped granular
Page 81 and 82: F ill dams It is therefore necessar
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Page 85 and 86: F ill dams 86 Case of compressible
Page 87 and 88: F ill dams In present practice, the
Page 89 and 90: F ill dams MONITORING SYSTEM 1 The
Page 91 and 92: F ill dams The most common measurem
Page 93 and 94: F ill dams 94 When H 2 V > 30, the
Page 95 and 96: F ill dams DESIGN OF THE FREE OVERF
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F ill dams 98 In the case of very w
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F ill dams TENDERING AND DAM CONSTR
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F ill dams In the case of a rock fo
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F ill dams However, when the materi
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F ill dams All of the inspections m
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F ill dams SPECIFIC FEATURES OF VER
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F ill dams !"engineering costs. The
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▲ 1 - Compacting clay in the cut-
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▲ 7 - Scarification after passage
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▲ 12 - Rip-rap on a dam built for
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▼ 20 - Overspill part of a side i
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C H A P T E R V Small concrete dams
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Chapter V Arch dams Arch dams trans
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Chapter V Masonry dams are no longe
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Chapter V Finally, the slope of the
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Chapter V FOUNDATION TREATMENT Hydr
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Chapter V and account will be taken
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Chapter V Thrust of ice This force
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Chapter V The commonly accepted cri
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Chapter V MONITORING SYSTEMS The ge
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Chapter V The typical cross-section
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Chapter V LOUBERRIA DAM Louberria d
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Chapter V Some of these barrages, a
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Chapter V Fig. 8 - Dam with a tilti
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Chapter V BIBLIOGRAPHY 1 - Ministè
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M anagement of water quality EUTROP
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M anagement of water quality !"the
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M anagement of water quality Proces
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M anagement of water quality 148 Al
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M anagement of water quality While
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M anagement of water quality It con
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M anagement of water quality It sho
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M anagement of water quality These
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4. Grégoire (A.), 1987- Caractéri
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L ife of the dam SPECIAL FEATURES O
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L ife of the dam GENERAL SURVEILLAN
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L ife of the dam ORGANISATION OF SU
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L ife of the dam During such period
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L ife of the dam MAINTENANCE 168 Th
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L ife of the dam BIBLIOGRAPHY 1 - C
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C onclusion FLOOD DATA It is fairly
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SMALL DAMS

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