Training Aids for Dam Safety Evaluation of Seepage Conditions EVALUATION OF SEEPAGE CONDITIONS TABLE OF CONTENTS Page UNIT I. OVERVIEW SIGNIFICANCE OF SEEPAGE PROBLEMS IN DAM SAFETY .....................................................I-1 Introduction............................................................................................................I-1 HISTORICAL PERSPECTIVE.................................................................................................I-2 Introduction............................................................................................................I-2 Early Methods Of Dam Design..................................................................................I-2 Current Practices In Dam Design..............................................................................I-2 Evolution Of Seepage Control Methods .....................................................................I-3 Current Practices In Seepage Control .......................................................................I-8 MODES OF FAILURE...........................................................................................................I-9 Introduction............................................................................................................I-9 Uplift, Heave, Or Blowout ........................................................................................I-9 Piping ................................................................................................................. I-11 Internal Erosion .................................................................................................... I-13 Solutioning ........................................................................................................... I-14 Internal Pressures And Saturation .......................................................................... I-15 Summary: Seepage Conditions............................................................................... I-17 UNIT II. REVIEW AND EVALUATION OF PROJECT DATA OVERVIEW .......................................................................................................................II-1 Introduction...........................................................................................................II-1 DOCUMENTATION REVIEW ...............................................................................................II-2 Introduction...........................................................................................................II-2 Documentation ......................................................................................................II-2 Field And Laboratory Investigations..............................................................II-3 Design Analyses And Construction Plans and Specifications............................II-3 Construction Reports, Logs, Records, Photographs, And As-Built Drawings ...............................................................................II-4 Operation And Maintenance Records ............................................................II-5 Instrumentation Records..............................................................................II-5 Past Inspection Reports ...............................................................................II-5 Relating Data to Visual Inspection ...........................................................................II-5 Continued… EVALUATION OF SEEPAGE CONDITIONS TABLE OF CONTENTS Page UNIT II. REVIEW AND EVALUATION OF PROJECT DATA Relating Data To Visual Inspection ..........................................................................II-6 SEEPAGE CONTROL MEASURES .........................................................................................II-7 Introduction...........................................................................................................II-7 Filters ..................................................................................................................II-7 Seepage Reduction Methods .................................................................................II-10 Embankment Seepage Reduction Methods.............................................................II-11 Flat Slopes ................................................................................................II-11 Thin Upstream Sloping Impervious Zone.....................................................II-11 Zoned Embankment With Impervious Core .................................................II-12 Anti-Seep Collars Around Conduits..............................................................II-14 Foundation And Abutment Seepage Reduction Methods..........................................II-15 Cutoffs .....................................................................................................II-15 Partial Cutoffs ...........................................................................................II-20 Upstream Impervious Blankets...................................................................II-21 Downstream Berms ...................................................................................II-22 Grouting ...................................................................................................II-22 Drainage Methods ................................................................................................II-24 Introduction..............................................................................................II-24 Pervious Shells ......................................................................................... II-25 Horizontal Drains.......................................................................................II-25 Chimney Drains.........................................................................................II-26 Filter Diaphragms Around Conduits.............................................................II-27 Toe (or Trench) Drains ..............................................................................II-28 Relief Wells...............................................................................................II-28 Structural Drain Methods-Concrete Dams...............................................................II-29 Introduction..............................................................................................II-29 Galleries And Relief Wells...........................................................................II-29 Drainage Adits And Lateral Drains Into Rock Abutments ..............................II-29 Structural Drain Methods-Appurtenant Structures...................................................II-30 Vertical Drains, Weep Holes, And Toe Drains ..............................................II-30 Geosynthetic Drains And Filters ..................................................................II-31 Sub-Drain Systems ....................................................................................II-31 SUMMARY .....................................................................................................................II-33 Review And Evaluation Of Project Data..................................................................II-33 Continued… EVALUATION OF SEEPAGE CONDITIONS TABLE OF CONTENTS Page UNIT III. FIELD INVESTIGATION OVERVIEW ................................................................................................................... III-1 Introduction......................................................................................................... III-1 Areas Of Investigation .......................................................................................... III-1 SOURCES OF DATA ......................................................................................................... III-3 Introduction......................................................................................................... III-3 Visual Evidence From Onsite Observation .............................................................. III-3 Interviews ........................................................................................................... III-3 Instrumentation ................................................................................................... III-4 Field Investigation................................................................................................ III-5 Laboratory Investigation....................................................................................... III-6 Laboratory Methods................................................................................... III-7 Field Methods............................................................................................ III-7 SPECIAL SEEPAGE CONDITIONS.....................................................................................III-10 Introduction........................................................................................................III-10 Field Observations...............................................................................................III-10 Evaluating Observations ......................................................................................III-11 Seepage Through Soluble Rock ............................................................................III-12 Seepage Through Dispersive Soils ........................................................................III-12 SUMMARY ....................................................................................................................III-13