Design Standards No. 13 Embankment Dams Chapter 8: Seepage Phase 4 (Final) U.S. Department of Interior Bureau of Reclamation January 2014 Mission Statements The U.S. Department of the Interior protects America’s natural resources and heritage, honors our cultures and tribal communities, and supplies the energy to power our future. The mission of the Bureau of Reclamation is to manage, develop, and protect water and related resources in an environmentally and economically sound manner in the interest of the American public. Design Standards Signature Sheet Design Standards No. 13 Embankment Dams DS-13(8)-4.1: Phase 4 (Final) January 2014 Chapter 8: Seepage Revision Number DS-13(8)-4.1 Summary of revisions: • A Foreword section was added before the Chapter Signature Sheet. • In Section 8.2.2.2, "High Exit Gradients in a Cohesionless Soil," on page 8-7, in the table appearing on that page, the "Recommended Safety Values" in column 2 were changed. • In Section 8.3.2.4, "Effect ofDegrce of Saturation on Permeability," on page 8-30, in the next to last paragraph on the page, the incorrect word "Note" was deleted. • On the cover, title page, and footers, the date was changed from "October 2011" to "January 2014." • Minor editorial corrections made throughout. Prepared by: Biii~P.E. Date Civil Engineer, Geotechnical Services Division Peer Review: tla'I/Z.otf Derek T. Wittwer, P.E. Date Civil Engineer, Geotechnical Engineering Group 4 Submitted: I I K~ Knighl,P£. Date Chief, Geotechnical Services Division Approved: Thomas A. Luebke, P.E. Date Director, Technical Service Center Foreword Purpose The Bureau of Reclamation (Reclamation) design standards present technical requirements and processes to enable design professionals to prepare design documents and reports necessary to manage, develop, and protect water and related resources in an environmentally and economically sound manner in the interest of the American public. Compliance with these design standards assists in the development and improvement of Reclamation facilities in a way that protects the public's health, safety, and welfare; recognizes needs of all stakeholders; and achieves lasting value and functionality necessary for Reclamation facilities. Responsible designers accomplish this goal through compliance with these design standards and all other applicable technical codes, as well as incorporation of the stakeholders’ vision and values, that are then reflected in the constructed facilities. Application of Design Standards Reclamation design activities, whether performed by Reclamation or by a non- Reclamation entity, must be performed in accordance with established Reclamation design criteria and standards, and approved national design standards, if applicable. Exceptions to this requirement shall be in accordance with provisions of Reclamation Manual Policy, Performing Design and Construction Activities, FAC P03. In addition to these design standards, designers shall integrate sound engineering judgment, applicable national codes and design standards, site-specific technical considerations, and project-specific considerations to ensure suitable designs are produced that protect the public's investment and safety. Designers shall use the most current edition of national codes and design standards consistent with Reclamation design standards. Reclamation design standards may include exceptions to requirements of national codes and design standards. Proposed Revisions Reclamation designers should inform the Technical Service Center (TSC), via Reclamation’s Design Standards Website notification procedure, of any recommended updates or changes to Reclamation design standards to meet current and/or improved design practices. Chapter Signature Sheet Bureau of Reclamation Technical Service Center Design Standards No. 13 Embankment Dams Chapter 8: Seepage DS-13(8)-4.11 Phase 4 (Final) Chapter 8 – Seepage is an existing chapter (last revised March 1987) within Design Standard 13 and was revised as follows: • Expanded discussion of seepage analysis principles and procedures • Expanded discussion of seepage mitigation measures • Revised discussion of seepage-related failure modes • Provided discussion for seepage monitoring • Provided discussion of key data for seepage evaluations • Added discussion of SEEP/W analyses and example problems • Provided illustrative considerations and examples of exit gradients and uplift pressures at the downstream toe of the embankment 1 DS-13(8)-4 refers to Design Standards No. 13, chapter 8, revision 4, minor intermediate revision 1. Prepared by: 407/ZiAti Bill Enge en, RE. Date Civil Engineer, Geotechnical Services Division Peer Review: LL JL-­ Derek T. Wittwer, RE. Date Civil Engineer, Geotechnical Engineering Group 1 Secur Review: 0/404/07 o il Larry K. •4( ss, P.E. Date Structu'll Engineer, Structural Analysis Group Recommended for Technical Approval: Thomas McDaniel Geotechnical Engineering Group 2 Submitted: /4,412 /2/ 03 'Oz.)/2 KaAren Knight, RE. D te Chief, Geotechnical Sericesl Division Approved: (7J- Z' Lowell Pimley, P.E. Date Director, Technical Service Center Design Standard No. 13, Chapter 8 Contents Page Chapter 8: Seepage 8.1 Introduction .............................................................................................. 8-1 8.1.1 Purpose ....................................................................................... 8-1 8.1.2 Scope .......................................................................................... 8-1 8.1.3 Deviations from Standard .......................................................... 8-1 8.1.4 Revisions of Standard ................................................................ 8-2 8.1.5 Applicability .............................................................................. 8-2 8.1.6 Definition of Terms.................................................................... 8-2 8.1.6.1 Seepage ...................................................................... 8-2 8.1.6.2 Pore Pressure .............................................................. 8-2 8.1.6.3 Phreatic Surface ......................................................... 8-2 8.1.6.4 Hydraulic Gradient..................................................... 8-2 8.1.6.5 Permeability ............................................................... 8-3 8.1.6.6 Anisotropy.................................................................. 8-3 8.1.6.7 Saturated Flow ........................................................... 8-3 8.1.6.8 Unsaturated Flow ....................................................... 8-3 8.1.6.9 Transient Flow ........................................................... 8-3 8.1.6.10 Seepage Force ............................................................ 8-3 8.1.6.11 Desiccation ................................................................. 8-4 8.1.6.12 Failure Mode .............................................................. 8-4 8.1.6.13 Internal Erosion .......................................................... 8-4 8.2 Seepage-Related Failure Modes .............................................................. 8-4 8.2.1 General ....................................................................................... 8-4 8.2.2 Excessive Exit Gradients and Uplift Pressures .......................... 8-5 8.2.2.1 General ....................................................................... 8-5 8.2.2.2 High Exit Gradients in a Cohesionless Soil ............... 8-5 8.2.2.3 Uplift of a Confining Soil Layer ................................ 8-7 8.2.2.4 Implications of High Vertical Exit Gradients and Uplift Pressures ........................................ 8-10 8.2.3 Unfiltered High Internal Gradients .......................................... 8-11 8.2.3.1 General ..................................................................... 8-11 8.2.3.2 Classical Piping ........................................................ 8-12 8.2.3.3 Internal Migration .................................................... 8-13 8.2.3.4 Scour ........................................................................ 8-13 8.2.3.5 Internal Instability, Suffusion, and Suffosion .......... 8-13 8.2.3.6 Analysis of Unfiltered High Internal Gradients ....... 8-14 8.2.3.7 Design Details to Protect Against High Internal Gradients ......................................................... 8-16 8.2.4 High Pore Pressures and Seepage Forces ................................ 8-16 8.2.5. Excessive Seepage Flows ........................................................ 8-17 8.2.6 Dissolution and Karst ............................................................... 8-17 8.2.7 Hydraulic Fracturing ................................................................ 8-18 8.2.8 Desiccation Cracking ............................................................... 8-19 DS-13(8)-4.1 January 2014 8-i Contents (continued) Page 8.2.9 Differential Settlement Cracking ............................................. 8-20 8.2.10 Additional Defects ................................................................... 8-21 8.2.11 Collapsible Soils ...................................................................... 8-21 8.3 Key Data for Seepage Evaluations ........................................................ 8-22 8.3.1 General ..................................................................................... 8-22 8.3.2 Permeability ............................................................................. 8-22 8.3.2.1 Estimating Permeability from