GEOTECHNICAL ENGINEERING OF EMBANKMENT DAMS

Transcription

1 GEOTECHNICAL ENGINEERING OF EMBANKMENT DAMS ROBINFELL Professar ofcivil Engineering School ofcivil Engineering, University ofnew South Wales, Sydney PATRICK MacGREGOR Chief Engineering Geo/ogist Snowy Mountains Engineering Corporation, Sydney DA VID STAPLEDON Geotechnical Consultant & Professar of Applied Geology University ofsouth Australia, Adelaide A.A. BALKEMA l ROTTERDAM l BROOKFIELD 11992

2 Contents PREFACE lx l EMBANKMENT DAMS, THEIR ZONING ANO SELECTION 1.1 Types of embankment dams, their advantages and limitations 1.2 Zoning of embankment dams and typical construction materials Selection of embankment type 17 2 WEATHERING PROCESSES AND PROFILES IN V ALLEYS I High horizontal stresses in rock Weathering of rocks Chemical alteration Rapid weathering Classification of weathered rock Landsliding 55 3 GEOTECHN ICAL QUESTIONS ASSOCIATED WITH VARIOUS GEOLOGICAL ENVIRONMENT$ Grani tic rocks Volcanic rocks (intrusive and flow) Pyroclastics Schistose rocks Mudrocks Sandstones and related sedimentary rocks Carbonate rocks l Alluvia1 soils Colluvial soils O Laterites and 1ateritic weathering profiles Glacial deposits and landforrns PLANNING, CONDUCTING AND REPORTING OF GEOTECHNICAL INVESTIGATIONS The need to ask the right questions Geotechnical input at various stages of project development 157 v

3 VI Geoter.:hn ù.:al engìneering of embankment dams 4.3 An iterative approach to the investigations Progression from regional to local studies Reporting Timing and funding of geotechnical studies The site investigation team SITE INVESTIGATION TECHNJQUES Topographic mapping and survey Interpretation of satellite images and aeri al photographs Geotechnica1 mapping Geophysical methods Test pits and trenches Adits and shafts Drill holes Sampling In situ testing O Groundwater In situ permeability tests on soil In situ permeability tests in rock Common errors an d defìciencies in geotechnica1 investigation 21 O 6 LABORATORY TESTING TECHNIQUES AND THEIR LIMITATIONS Shear strength of soils Shear strength of rock Permeability of soils DESIGN, SPECIFICATION AND CONSTRUCTION OF FILTERS l Basic requirements for fìlters Filterdesign methods Specifìcation of size and durability of fìlters Dimensions, placement and compaction of fìlters Use of geotextiles as fìlters in dams CLA Y MINERALOGY, SOIL PROPERTIES, DISPERSIVE SOILS AND PIPING FAILURE Introduction Clay minerals and their structure Interaction between water and clay minerals ldentifìcation of clay minerals Engineering properties of clay soils related to the types of clay minerals present Identifìcation of dispersive soils Use of dispersive soi1s in embank:mentdams DAMS ON HIGHL Y PERMEABLE SOIL FOUNDATIONS Generai description of the special problems 318

4 Contents VII 9.2 Contro! of erosion and 'blowup' or Iiquefaction of the foundation 9.3 Contro! ofunderseepage by cutoffs 10 STABILITY ANALYSIS l 0.1 Generai principles l 0.2 Estimation of pore pressure l 0.3 Analysis of stability Il FOUNDATION PREPARATION ANO CLEANUP Il. l Generai requirements l 1.2 Generai foundation preparation 11.3 Cutoff foundation l 1.4 Width and batter slopes for cutoff 11.5 Selection of cutoff foundation criteria 11.6 Slope modification and seam treatment 12 FOUNDATIONGROUTING 12.1 Generai concepts of grouting dam foundations 12.2 Grouting design - Cement grout 12.3 Some practical aspects of grouting with cement 12.4 Chemical grouts in dam engineering 13 EMBANKMENTDETA~S 13.1 Freeboard 13.2 Embankment crest details 13.3 Embankment dimensioning and tolerances 13.4 Slope protection 13.5 Conduits through embankments 13.6 Interface between earthfill and concrete structures 13.7 Flood contro! structures 13.8 Design of dams for overtopping during construction 14 SPECIFICA TION ANO QUALITY CONTRO L OF EARTHFILL ANDROCKF~L 14.1 Specification of rockfill 14.2 Specification of earthfill 14.3 Quality contro! 14.4 Testing of rockfill 14.5 Testing of earthfill 15 DESIGN OF DAMS TO WITHSTAND EARTHQUAKES 15.1 Effect of earthquake on embankment dams 15.2 Assessment of design earthquake 15.3 Liquefaction of dam embankments and foundations 15.4 Evaluation of liquefaction potential 15.5 Analysis of stability and deformations 15.6 Design for earthquake

5 v III Geotechnical engineering of embankment dams 16 CONCRETE FACEROCKFILLDAMS Generai arrangement and reasons for selecting this type of da m 16.2 Rockfi Il zones and their properties 16.3 Concrete face 16.4 Construction aspects 16.5 Some non-standard design features 17 MINE AND INDUSTRIAL TAILINGS DAMS 17.l Generai 17.2 Tailings and their properties 17.3 Methods of tailings discharge and water recovery 17.4 Prediction of tailings properties 17.5 Methods of construction of tailings 'dams' 17.6 Seepage from tailings dams and its contro! 18 MONITORING ANO SURVEILLANCE OF EMBANKMENT DAMS 18.1 What is monjtoring and survei llance? 18.2 Why undertake monitoring and surveillance? 18.3 What monitoring is required? 18.4 How is the monitoring done? 18.5 Ho w often stiould monitoring be carri ed out? REFERENCES SUBJECT INDEX