SMALL DAMS

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Chapter II C H A P T E R I I I Geological and geotechnical studies Chairman: Patrice BRUNEL (CARA) Committee members: Emmanuel ALONSO (Cemagref), Jean-Pierre BECUE (SAFEGE), Jean-Luc BRODIN (CACG), Bernard COUTURIER (BRL), Danièle LAUTRIN (Cemagref) and Georges MICHEL (SCP). On the topic of geological and geotechnical studies, special attention is given to: !"the various techniques available; !"identification and choice of a dam site; !"geological and geotechnical studies and site investigations to adapt the dam project to the chosen site, in particular including the choice of the most suitable type of dam for the site; !"geological supervision during dam construction. 37 PRELIMINARIES This chapter is intended to give some recommendations based on the authors' experience and current practice. Given the specific nature of geological and geotechnical problems, no typical program can be given but the minimum that is usually accepted is stated. In fact, the fundamental importance of knowledge of the geological and geotechnical context in which the dam will be built, combined with the great variety of foundations that might be encountered, making each dam project unique, preclude any prior definition of the extent and nature of the required site investigations.
G eological and geotechnical studies Only an experienced professional has the competence to adapt the studies undertaken to the geological context that they gradually reveal and to identified or assumed problems, following an iterative process that usually results in a site investigation program planned in several stages (with the orientation and contents of each stage defined as the preceding stage is concluded). Those site investigations should make it possible to avoid, insofar as is possible, encountering any unforeseen problem as the dam is built, leading to improvisation, cost overruns and delays, which are always adverse (especially when the dam is small and financing generally limited with little margin). Herein we successively look at: !"the various techniques used in geological and geotechnical studies for dam projects; !" methodological recommendations concerning the various stages in the geological and geotechnical investigations, from site identification to construction. The basic concepts of geotechnics and rock mechanics are assumed to be familiar to the reader who, if necessary, may refer to the many specialised manuals published in those fields. 38 TECHNIQUES This section looks at all of the techniques that are applicable to dams under a height of about 25 metres. Depending on the nature of the site and the size of the dam, only some of these techniques may need to be employed. SITE INVENTORY A systematic inventory of dam sites is undertaken when there is a need to find potential storage sites to meet specific needs for water resources within a given area, which may be small (a catchment area measuring a few hundred hectares) or vast (a large catchment area measuring several hundred square kilometres). This approach makes use of several techniques: !"desk study using topographical maps of a scale suited to the size of the envisaged reservoir (1/25 000 for the dams addressed in this document, bearing in mind that very small sites are not identifiable at that scale); !" aerial photography (stereo pairs); !" direct field investigation. These three techniques are very complementary and it is always preferable to combine them whenever possible, as each provides information that helps to better assess the characteristics of the site:
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
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Page 15 and 16: W hat need for guidelines for small
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Page 23 and 24: P reliminary determination of desig
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Page 39 and 40: G eological and geotechnical studie
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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
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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
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F ill dams In present practice, the
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F ill dams MONITORING SYSTEM 1 The
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F ill dams The most common measurem
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F ill dams 94 When H 2 V > 30, the
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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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