NB/T 10872-2021Code for design of roller-compacted embankment dams (English PDF)

Foreword

This document was issued on 22 December 2021 by the National Energy Administration of the PRC and takes effect on 22 June 2022.

It is a NB/T standard: recommended rather than compulsory, but it is the text a Chinese reviewer applies when assessing a submission.

It is classified under ICS 27.140, Chinese classification P 59.

It replaces DL/T 5395-2007, which is superseded.

This code has been revised in accordance with the requirements of the Notice of the National Energy Administration on Issuing the 2015 Plan for the Development and Revision of Sector Standards in the Field of Energy (Guo Neng Ke Ji [2015] No. 283). The drafting group carried out extensive investigation and research, summarized practical engineering experience in earnest, and prepared the revision on the basis of a wide solicitation of comments.

The main technical contents of this code are: general provisions; terms and symbols; basic requirements; dam type selection and project layout; selection and design of embankment materials; dam structure; dam foundation treatment; connection between the dam and other structures; calculation and analysis of embankment dams; staged construction and dam heightening; instrumentation design; construction requirements; and initial impoundment, operation and maintenance.

The main technical changes introduced by this revision are the following.

The terms contact soil, special soil, soft clay and slightly cohesive soil have been added.

Requirements have been added for the provision of release facilities in structures used to draw down the reservoir water level.

Requirements have been added for the physical and mechanical indices of gravelly soil used as the impervious element.

Requirements have been added for the material properties and compaction of contact soil.

Requirements have been added for the zoning of extra-high dams of 200 m in height and above and for the filling and rolling indices of each material zone.

A requirement has been added for providing a transition zone at the junction between the dam shell material and rigid structures or the abutment slopes.

Provisions have been added for grouting galleries and for the concrete cover slab of the foundation.

Requirements have been added for consolidation grouting of sand and gravel foundations.

Criteria have been added for the safety factors against sliding of extra-high dams of 200 m in height and above.

Provisions have been added for the seismic design of embankment dams.

A chapter entitled Construction Requirements has been added, covering the use of construction information technology.

A chapter entitled Initial Impoundment, Operation and Maintenance has been added.

The scope of application and the classification of dams by height have been revised.

The scope of application of soft rock used as embankment material and the corresponding engineering measures have been revised.

The values of the partial coefficients used in the calculation of the sliding stability of the dam body have been revised.

The requirements and methods for the calculation of stress and deformation of the dam body and for three-dimensional seepage analysis have been improved.

The requirements for the flood-retaining standard during the construction period and for the filling elevations have been deleted.

The construction requirements for the closure section have been deleted.

This code is under the administration of the National Energy Administration. The China Renewable Energy Engineering Institute has proposed the code and is responsible for its routine administration. The Energy Sector Standardization Technical Committee for Hydropower Investigation and Design (NEA/TC15) is responsible for the interpretation of its specific technical contents. Comments and suggestions arising during implementation should be sent to the China Renewable Energy Engineering Institute (address: No. 2 Liupukang Beixiaojie, Xicheng District, Beijing; postcode 100120).

Chief development organizations: PowerChina Northwest Engineering Corporation Limited and the China Renewable Energy Engineering Institute.

Participating development organizations include PowerChina Chengdu, Kunming, Beijing, Guiyang, Zhongnan and Huadong Engineering Corporations Limited, the China Institute of Water Resources and Hydropower Research, the Nanjing Hydraulic Research Institute, Hohai University, Wuhan University and Guoneng Dadu River Basin Hydropower Development Co., Ltd.

Scope of the Code and Arrangement of Its Chapters

The English contents page printed in the standard shows how the design process is ordered. Chapter 3, Basic Requirements, begins on page 9 and sets out the general design requirements that apply throughout, including dam classification and the safety criteria referred to by the later chapters.

Chapter 4, Dam Type Selection and Project Layout, begins on page 11 and is divided into 4.1 Dam Type Selection, 4.2 Dam Axis, and 4.3 Layout of Water Release and Conveyance Structures.

Under 4.3 the foreword records a new requirement of this edition: release facilities are to be provided in the structures used to draw down the reservoir water level.

Chapter 5, Selection and Design of Embankment Materials, begins on page 14 and comprises 5.1 General Requirements, 5.2 Embankment Material Selection and Parameters, and 5.3 Filling and Compaction Requirements.

Two of the additions announced in the foreword belong to Chapter 5: the physical and mechanical indices required of gravelly soil used as an impervious element, and the material and compaction requirements for contact soil.

The revision also restates the permitted scope of use of soft rock as embankment material and the engineering measures to be taken with it.

Chapter 6, Dam Structure, begins on page 23 and is the longest chapter of the code, running to eleven subclauses.

Its subclauses cover embankment zoning, dam slope and berm, freeboard and settlement, crest detailing, the impervious element, filter, cushion and transition zones, dam drainage, slope protection and dam face drainage.

The last two subclauses of Chapter 6 deal with the foundation and abutment galleries of clay core embankment dams and with the concrete cushion plate of such dams; both correspond to provisions newly added by this revision on grouting galleries and the concrete cover slab of the foundation.

Chapter 6 also carries the new zoning requirements for extra-high dams of 200 m in height and above, and the requirement for a transition zone where the dam shell material meets rigid structures or the abutment slopes.

Chapter 7, Dam Foundation Treatment, begins on page 37 and is divided into general requirements, sand and gravel foundation treatment beginning on page 37, rock foundation treatment beginning on page 44, and special soil foundation treatment beginning on page 48.

The requirement for consolidation grouting of sand and gravel foundations that the foreword lists among the additions belongs to 7.2.

Chapter 8, Connection Between Dam and Other Structures, occupies pages 50 and 51 and governs the junctions between the embankment and adjoining concrete structures, abutments and conduits.

Chapter 9, Embankment Dam Calculation and Analysis, begins on page 52 and contains 9.1 Seepage and Seepage Stability Calculation and Analysis, 9.2 Sliding Stability Calculation and Analysis, and 9.3 Stress and Deformation Calculation and Analysis.

In Chapter 9 the values of the partial coefficients used in the calculation of the sliding stability of the dam body have been revised, the safety factors against sliding for extra-high dams of 200 m and above have been added, and the requirements and methods for stress and deformation analysis and for three-dimensional seepage analysis have been improved.

The provisions on the seismic design of embankment dams are also new in this edition.

Chapter 10, Staged Construction and Dam Heightening, begins on page 62 and is divided into 10.1 Staged Construction and 10.2 Dam Heightening.

Chapter 11, Instrumentation Design, begins on page 65 and comprises general requirements, monitoring items, and the processing and analysis of monitoring data.

Chapter 12, Construction Requirements, beginning on page 69, is a chapter newly added by this revision and includes matters relating to construction information technology; the requirements of the previous edition for the flood-retaining standard during construction, the filling elevations and the closure section have been deleted.

Chapter 13, Initial Impoundment, Operation and Maintenance, beginning on page 71, is likewise new in this edition and closes the design sequence at the point where the completed dam is first put into service.

Appendices and Supplementary Material

Seven appendices follow the thirteen chapters and carry the calculation methods on which the design provisions rely.

Appendix A, Calculation of Wave and Slope Protection, begins on page 73 and supports the freeboard requirements of 6.3 and the slope protection requirements of 6.8.

Appendix B, Filter Zone Design, begins on page 86 and supports subclause 6.6 on filter, cushion and transition zones.

Appendix C, Seepage Calculation Method and Seepage Stability Criteria, begins on page 90 and is the longest appendix, running to seventeen pages; it applies the definitions of soil flow and piping given in Chapter 2.

Appendix D, Sliding Stability Analysis, begins on page 107 and supports subclause 9.2.

Appendix E, Determination of Shear Strength of Embankment Materials, begins on page 119.

Appendix F, Stress and Deformation Analysis, begins on page 122 and supports subclause 9.3.

Appendix G, Tests and Parameter Determination for Embankment Materials, begins on page 131 and supports the material parameter requirements of 5.2.

The Explanation of Wording in This Code on page 135 defines the degrees of obligation attached to the auxiliary verbs used in the provisions.

The List of Quoted Standards on page 136 gives the other standards referred to in the text.

The Addition, Explanation of Provisions, begins on page 139 and gives the drafting group's commentary on the individual clauses.

1 Scope

NB/T 10872-2021 is the Chinese design code for roller-compacted earth and rockfill dams, replacing DL/T 5395-2007. It governs the design of embankment dams built by placing and compacting soil, gravel and rock in layers, across the full range of dam classes and heights used on hydropower and water resources projects. The code begins with the general provisions and a full set of defined terms, then works through the design in the order an engineer meets it: selection of the dam type and axis, the zoning of the embankment and the choice of materials for each zone, the investigation and testing of borrow areas, and the design of the impervious element - central or inclined clay core, concrete face slab, or asphaltic concrete. Filters and transitions, drainage systems, the foundation and its treatment including cut-offs and grout curtains, and the seepage analysis that ties them together each receive their own treatment. Stability analysis under construction, steady seepage, rapid drawdown and seismic loading is set out with the methods and the safety factors required. Settlement and deformation, slope protection against wave and ice action, the crest and its freeboard, and the instrumentation installed to monitor the dam in service complete the document. It applies to the feasibility, preliminary and detailed design stages of embankment dams in China, and is the text a Chinese reviewer applies when assessing such a design.

1.0.1 This code has been formulated in order to standardize the design of roller-compacted embankment dams, so that such designs are safe and reliable, economically rational, technically advanced, environmentally friendly and sparing of resources.

1.0.2 This code applies to the design of roller-compacted embankment dams of hydropower projects that are newly built, rebuilt or extended.

1.0.3 In addition to complying with this code, the design of roller-compacted embankment dams shall also comply with the provisions of the relevant current national standards.

The three general provisions above set the purpose, the field of application and the relationship of this code to other standards. They make clear that the code is written for hydropower engineering practice and that it does not stand alone: national standards on loads, seismic design, concrete, grouting, foundation investigation and construction remain applicable alongside it.

The publication data of the code are stated on its cover: it was issued by the National Energy Administration on 22 December 2021 under Announcement No. 6 of 2021 and came into force on 22 June 2022, replacing DL/T 5395-2007.

2 Terms and Symbols

Chapter 2 is divided into 2.1 Terms, which begins on page 2, and 2.2 Symbols, which begins on page 5. The terms are given in Chinese with their English equivalents and are followed by a definition; the symbols subclause lists the notation used in the formulas of the code and in its appendices.

2.1.1 embankment dam: a dam built by filling with local materials such as soil, sand and gravel, and rock.

2.1.2 roller-compacted embankment dam: an embankment dam in which the earth and rockfill materials are placed in layers and compacted dense by rolling.

2.1.3 homogeneous earth dam: a dam whose cross section is not divided into an impervious element and dam shells, the greater part of the section consisting of a single impervious soil material.

2.1.4 zoned embankment dam with earth impervious element: a dam whose cross section is formed by an earth impervious element together with a number of zones of earth and rockfill materials of differing permeability.

2.1.5 zoned embankment dam with non-earth impervious element: a dam in which the impervious element consists of concrete, asphalt concrete, a geomembrane or similar material, while the remainder of the section is formed of earth and rockfill materials.

2.1.6 dam axis: the line representing the plan position of the dam across the river valley; for an embankment dam the centre line of the dam crest is generally taken as the axis.

2.1.7 dam length: the length measured along the dam axis between the two ends of the dam crest.

2.1.8 dam height: the height measured from the base of the impervious element of the dam, or from the foundation surface at the position of the dam axis, up to the dam crest, excluding foundation seepage-control works such as concrete cut-off walls, grout curtains and cut-off trenches; the greater of the two values is taken.

2.1.9 dam crest: the top surface of the dam body.

2.1.10 dam slope: the slope of the upstream and downstream faces of the dam body.

2.1.11 berm: a platform of a certain width provided at a suitable position on the slope of an embankment dam to meet the needs of construction, observation, maintenance and traffic.

2.1.12 parapet wall: a wall provided along the water-retaining edge of the dam crest to prevent waves from overtopping the crest.

2.1.13 cohesionless soil: a soil in which the content by mass of clay particles finer than 0.005 mm is not greater than 3 percent, whose plasticity index is not greater than 3, and whose particles have no cohesive bond between them.

2.1.14 gravelly soil: a soil material composed of particles such as cobbles or crushed stone, gravel, sand, silt and clay particles, including natural soils, artificially blended soils, and the various widely graded soils formed after rolling of weathered rock or soft rock.

2.1.15 impervious soil: a soil material used for the impervious element of an embankment dam and possessing an imperviousness function.

2.1.16 contact soil: a cohesive soil material used at the position where the earth impervious element meets a rigid structure or the dam foundation, in order to make the deformations of the two compatible.

2.1.17 special soil: a cohesive soil material with a special material composition, structure and distinctive engineering properties, including red clay, expansive soil, collapsible loess and dispersive clay.

2.1.18 expansive soil: a highly plastic soil rich in hydrophilic minerals, showing marked swelling on absorbing water and shrinkage on losing water.

2.1.19 dispersive clay: a cohesive soil in which, in water of low salt content or in pure water, the repulsive forces between the ions exceed the attractive forces, so that the soil particles disperse.

2.1.20 soft clay: a fine-grained soil with a natural void ratio greater than or equal to 1.0 and a natural water content greater than the liquid limit, having high compressibility, low strength, high sensitivity, low permeability and high creep deformation, and liable to seismic settlement under a relatively large earthquake action; it includes mud, muddy soil, peat and peaty soil.

2.1.21 organic soil: a soil with an organic matter content greater than or equal to 5 percent and less than or equal to 10 percent.

2.1.22 peaty soil: a soil containing a large amount of undecomposed humus, with an organic matter content greater than 10 percent and less than or equal to 60 percent.

2.1.23 peat: a soil containing a large amount of undecomposed humus and with an organic matter content greater than 60 percent.

2.1.24 collapsible loess: a loess whose structure is rapidly destroyed when it is soaked with water under a given pressure, producing a significant additional settlement.

2.1.25 red clay: a highly plastic clay of brown-red or brownish-yellow colour, with a liquid limit greater than or equal to 50 percent, formed by relatively complete chemical weathering of the rocks of outcrop areas of carbonate rock series, occurring as residual slope deposits or after transport and redeposition, and existing in the form of an aggregate structure.

2.1.26 gap-graded soil: a soil material whose particle size distribution curve has at least one flat segment where the content of particles of a given size fraction is not greater than 3 percent.

2.1.27 soil flow: the phenomenon in which, under the action of seepage, the surface of a local soil mass heaves or is pierced, or in which coarse and fine particles float and are lost together.

2.1.28 piping: the phenomenon in which fine particles within a soil mass are lost through the pore channels of the skeleton under the action of seepage.

The definitions of soil flow and piping introduce the seepage stability criteria that are applied in Chapter 9 and in Appendix C, while the definitions of the several special soils are the basis of the special soil foundation treatment requirements of 7.4.