NB/T 10867-2021Code for design of spillways (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It replaces DL/T 5166-2002, which is superseded.

This code was revised in accordance with the requirements of the Notice of the National Energy Administration on Issuing the First Batch of Development and Revision Plans for Industry Standards in the Energy Sector for 2009 (Guo Neng Ke Ji [2009] No. 163). The drafting group carried out extensive investigation and research, carefully summarized practical experience and solicited opinions widely before completing the revision.

The main technical contents of this code are: general provisions; terms and symbols; basic requirements; layout of the spillway; hydraulic design; structural design; foundation and slope treatment design; safety monitoring design; construction requirements; and operation and maintenance requirements.

The main technical contents revised in this edition are listed below.

Provisions concerning the design of tunnel spillways have been added.

Provisions concerning the reasonable service life of the spillway and concerning design against ice and freezing have been added.

Two new chapters, Construction Requirements and Operation and Maintenance Requirements, have been added.

The provisions on the grade of the spillway and of the energy dissipation and erosion control structures, and on the corresponding flood standards, have been revised.

The provisions on the anti-floating stability of the stilling basin slab and on the structural design of gravity sidewalls along the straight section of the chute have been revised; the single safety factor method is adopted for structural stability calculation, corresponding safety evaluation criteria are proposed, and Appendix C and Appendix D of the former code have been revised accordingly.

Appendix A of the former code has been revised, with the addition of hydraulic calculation formulas for flow fluctuation and aerated water depth in the chute, hydraulic calculation formulas for bottom-flow hydraulic jump energy dissipation, and criteria for discriminating the flow regimes of stepped energy dissipation.

The contents concerning probabilistic limit state design and the related calculations in structural design have been deleted.

The contents concerning overflow weirs with breast walls have been deleted.

This code is under the administration of the National Energy Administration. It was proposed by, and is under the day-to-day administration of, China Renewable Energy Engineering Institute. The Energy Industry Standardization Technical Committee for Hydropower Survey and Design (NEA/TC15) is responsible for the interpretation of its specific technical content.

Comments and suggestions arising during the implementation of this code should be sent to China Renewable Energy Engineering Institute, No. 2 Liupukang Beixiaojie, Xicheng District, Beijing, postcode 100120.

Chief development organization of this code: PowerChina Zhongnan Engineering Corporation Limited.

Chief drafters of this code: Feng Shurong, Pan Jiangyang, Zhou Yuefei, Zhang Jianguo, Zhao Hongmin, Miao Baoguang, Li Yannong, Dai Xiaobing, Su Junan, Wen Fuyong, Zhang Jinwan, Liu Yaolai, Peng Kai, Wang Xiaoliang, Liu Dong, Ye Xiangfei, Li Yonggang, Cao Yuanyuan.

Chief examiners of this code: Zhou Jianping, Zhao Quansheng, Li Yonghong, Xiao Feng, Wang Fuqiang, Wei Yongxin, Zhang Yongtao, Hu Xiaoyun, Yang Zaihong, Mu Hongyou, Du Xiaokai, Wang Yuansheng, Long Wen, Chen Zhenwen, Li Yuetao, Sun Shuangke, Han Changhai, Liu Shanjun, Yin Jinbu, Zhang Dongsheng, Li Shisheng.

Publication data

Designation: NB/T 10867-2021, an energy industry standard of the People's Republic of China. The cover carries the classification data ICS 27.140 and the Chinese Standard Classification Code P 59, together with the sector letter P used on energy industry standards for water resources and hydropower engineering.

Chinese title as printed on the cover: Yi Hong Dao She Ji Gui Fan. Official English title as printed on the cover and on the title page: Code for Design of Spillways.

Replaced standard: this code supersedes DL/T 5166-2002, the previous edition of the design code for spillways, as stated by the line printed under the designation on the cover.

Issue date 2021-12-22 and implementation date 2022-06-22, both printed on the cover; the title page repeats the date of entry into force as 22 June 2022. The issuing authority is the National Energy Administration of the People's Republic of China.

Administering department named on the title page: China Renewable Energy Engineering Institute (the General Institute of Hydropower and Water Resources Planning and Design). Approving department: National Energy Administration. Publisher: China Water and Power Press, Beijing, 2022.

Approval instrument: Announcement No. 6 of 2021 of the National Energy Administration, dated 22 December 2021. Under the Standardization Law of the People's Republic of China and the Measures for the Administration of Energy Standardization, the Announcement approved 356 energy industry standards (Annex 1) and 25 foreign-language versions of energy industry standards (Annex 2). In the Annex 1 catalogue this code appears as item 18: standard number NB/T 10867-2021, replacing DL/T 5166-2002, approval date 2021-12-22, implementation date 2022-06-22.

Structure of the document

The code is organised in ten chapters followed by four appendices and the usual closing matter. The official English table of contents printed in the standard is reproduced word for word in the index of this listing.

Chapters 1 to 3 set the framework: General Provisions (page 1), Terms and Symbols with the two sub-clauses Terms and Symbols (page 2), and Basic Requirements (page 6).

Chapter 4, Layout of Spillway (page 8), covers General Requirements, Entrance Channel, Control Section, Chute, Energy Dissipation and Erosion Control Facilities and Outlet Channel, that is, the layout of the spillway component by component from the intake to the discharge back into the river.

Chapter 5, Hydraulic Design (page 16), follows the same component sequence and adds Cavitation Control, Flood Discharge Atomization Study and Ice Control and Defence.

Chapter 6, Structural Design (page 23), covers the lining of entrance and outlet channels, the control section, the chute invert, the flip bucket, the stilling basin slab, the sidewall and the downstream protection.

Chapter 7, Foundation and Slope Treatment Design (page 31), covers foundation excavation, consolidation grouting, foundation seepage control and drainage, treatment of faults, soft interlayers and karst, and slope excavation and slope treatment.

Chapters 8 to 10 cover Safety Monitoring Design (page 37), with general requirements and monitoring items and contents, Construction Requirements (page 39) and Operation and Maintenance Requirements (page 40).

The appendices carry the calculation procedures: Appendix A Hydraulic Calculation (page 41), Appendix B Cavitation Control Design for High Speed Flow Area (page 70), Appendix C Anti-floating Stability Calculation for Stilling Basin Slab (page 80) and Appendix D Structural Calculation of Gravity Sidewalls for Chute Straight Section (page 85). They are followed by the Explanation of Wording in This Code (page 89), the List of Quoted Standards (page 90) and the Addition: Explanation of Provisions (page 91).

1 Scope

NB/T 10867-2021 is the Chinese design code for spillways, replacing DL/T 5166-2002. The spillway is the structure that decides whether a dam survives its design flood, and on most Chinese schemes it is a separate chute cut into the abutment rather than an overflow over the dam itself. The code sets the general provisions, the defined terms and symbols, and the basic requirements: the spillway class following from the dam class, the design and check flood standards, the safety factors and the arrangement options - open chute, side channel, shaft and tunnel spillways, and the choice between gated and ungated control. Hydraulic design follows: the discharge capacity of the control section and the shape of the overflow crest, the water surface profile down the chute, the air entrainment and the freeboard, the cavitation index and the aeration devices that protect the floor at high velocity, and the energy dissipation and scour control at the outlet. Structural design covers the control structure and its piers and gates, the chute floor slabs and their anchorage, drainage and joints, the training walls, and the cut slopes and their support. Foundation treatment, the protection of the downstream channel and the banks, and the arrangements for passing floods during construction are all specified, with monitoring instrumentation and the operating rules closing the code. It applies to hydropower and water resources projects in China.

Chapter 1 states the purpose of the code, the works to which it applies and its relationship with the other standards in force.

1.0.1 This code is formulated in order to standardize the design of spillways of hydropower projects and to guarantee design quality, so that the design meets the requirements of safety and reliability, economic rationality, technical advancement, environmental friendliness, resource saving and convenience of management and operation.

1.0.2 This code applies to the design of bank-side open channel spillways and of tunnel spillways founded on rock, for newly built, rebuilt and extended hydropower projects.

1.0.3 In addition to complying with this code, the design of spillways shall also comply with the provisions of the relevant national standards currently in force.

2 Terms and symbols

Clause 2.1 Terms. The code defines twenty-three terms, each given in Chinese with its official English equivalent; the definitions are reproduced in full below.

2.1.1 open channel spillway — a spillway in which both the inlet control section and the chute are open, that is, unroofed.

2.1.2 tunnel spillway — a spillway wholly or partly formed as a tunnel inside the hillside on the bank, in which the flow has a free surface over its whole length; also called a spillway tunnel.

2.1.3 emergency spillway — a spillway used to discharge abnormal floods exceeding the design flood standard.

2.1.4 entrance channel — the channel located upstream of the control section which leads the flow to the control section of the spillway; it may be a channel of full cross section or of partial cross section.

2.1.5 control section — the weir, gate and connecting structures on both sides, located between the entrance channel and the chute, which control the discharge of the spillway.

2.1.6 chute — the steep-slope discharge channel between the outlet of the control section and the energy dissipation section.

2.1.7 ski-jump energy dissipation — a mode of energy dissipation in which a flip bucket is provided at the outflow end of the discharge structure, so that the supercritical flow leaving the structure is thrown into the air and falls as an aerated jet onto the downstream water cushion.

2.1.8 flip bucket — a bucket built at the end of a discharge structure, having a certain reverse-arc radius and a certain deflection angle, able to project the high velocity flow being discharged towards the downstream; also called a flip bucket nose.

2.1.9 continuous flip bucket — a continuous solid flip bucket built at the end of a discharge structure.

2.1.10 slotted flip bucket — a flip bucket formed of alternating teeth and slots, or made up of parts set at different elevations or with different deflection angles.

2.1.11 slit-type bucket — a flip bucket in which the sidewalls of the chute contract sharply at the outlet of the supercritical flow so as to form a narrow slit.

2.1.12 special-shaped flip bucket — a flip bucket of special body shape formed by twisting the invert surface, by cutting the corners of the bucket lip or by other means.

2.1.13 hydraulic jump energy dissipation — a mode of energy dissipation in which the hydraulic jump dissipates the residual energy of the supercritical flow discharged along the bottom of the discharge structure, turning the supercritical flow into subcritical flow which joins the downstream flow.

2.1.14 stilling basin — an energy dissipation facility placed at the outlet of a discharge structure and made up of sidewalls, a slab, an end sill, an apron and similar parts, designed according to the requirements of hydraulic jump energy dissipation.

2.1.15 apron — a rigid bed-protection structure built downstream of an energy dissipation structure to protect the river bed from scouring damage.

2.1.16 surface flow energy dissipation — a mode of energy dissipation in which a drop sill or a small flip bucket at the end of the discharge structure throws the main body of the supercritical flow up to the water surface, and the energy of the discharged flow is dissipated by surface diffusion, by the bottom roller and by the surface roller.

2.1.17 bucket-type flow energy dissipation — a mode of energy dissipation in which a bucket is provided at the end of the discharge structure so that the discharge is thrown to the water surface, and the energy of the discharged flow is dissipated by the roller inside the bucket, by the bottom roller and by the surface roller.

2.1.18 outlet channel — the discharge channel that leads the flow, after energy dissipation, smoothly into the downstream river course.

2.1.19 cavitation — the flow phenomenon in which cavities appear, involving the inception, growth and collapse of the cavities, when the absolute pressure at some point in a high velocity flow falls below the vapour pressure at that point.

2.1.20 cavitation number — a dimensionless parameter, composed of the pressure head and the velocity head of the flow, that describes the state of cavitation.

2.1.21 incipient cavitation number — when flow passes a boundary wall of a given geometric shape and the cavitation number of the flow reaches a certain critical value, cavitation begins to occur at some point on the wall; the cavitation number of the flow at that moment is called the incipient cavitation number of that body shape at that location.

2.1.22 cavitation damage — the erosion and destruction of a solid boundary caused by cavitation.

2.1.23 flood discharge atomization — the physical phenomenon in which rain and mist are formed during the flood discharge of a hydropower project by the break-up of the discharged flow, by the splashing of the water surface and by collisions in the air.

Clause 2.2 Symbols. The symbols are grouped into geometric features, material properties, hydraulic calculation parameters and hydraulic calculation coefficients.

2.2.1 Geometric features. P1 — upstream weir height.

2.2.1 Geometric features. P2 — downstream weir height.

2.2.1 Geometric features. D — height of the orifice.

2.2.1 Geometric features. R — radius of the reverse arc.

2.2.2 Material properties. gamma R prime — buoyant unit weight of the rock mass.

2.2.2 Material properties. C — symbol of the strength grade of concrete.

2.2.2 Material properties. f prime — friction coefficient for shear rupture on the contact surface between concrete and bedrock.

2.2.2 Material properties. c prime — cohesion for shear rupture on the contact surface between concrete and bedrock.

2.2.3 Hydraulic calculation parameters. H — difference between the upstream and the downstream water levels.

2.2.3 Hydraulic calculation parameters. H1 — upstream water depth.

2.2.3 Hydraulic calculation parameters. H2 — downstream water depth.

2.2.3 Hydraulic calculation parameters. h — water depth at the cross section.

2.2.3 Hydraulic calculation parameters. v — flow velocity.

2.2.3 Hydraulic calculation parameters. Q — discharge.

2.2.3 Hydraulic calculation parameters. q — discharge per unit width.

2.2.3 Hydraulic calculation parameters. Hd — design head of the weir profile.

2.2.3 Hydraulic calculation parameters. H0 — head on the weir crest.

2.2.3 Hydraulic calculation parameters. H max — maximum head.

2.2.3 Hydraulic calculation parameters. i k — critical slope of the channel.

2.2.3 Hydraulic calculation parameters. h k — critical water depth.

2.2.4 Hydraulic calculation coefficients. Fr — Froude number.

2.2.4 Hydraulic calculation coefficients. sigma — cavitation number of the flow.

2.2.4 Hydraulic calculation coefficients. m — discharge coefficient of the overflow weir.

2.2.4 Hydraulic calculation coefficients. sigma m — submergence coefficient.

2.2.4 Hydraulic calculation coefficients. phi — velocity coefficient.

3 Basic requirements

Chapter 3 sets the general design requirements for the spillway: the basic data to be collected, the grade of the works and the flood standards, the behaviour to be accepted under floods exceeding the design standard, the operating rules and the service life, and the hydraulic studies to be carried out.

3.0.1 The design of a spillway shall collect and analyse basic data on meteorology, hydrology, sediment, topography, geology, earthquake, construction materials, ecology and environment.

3.0.2 The grade of the spillway and of the energy dissipation and erosion control structures, and the discharge standards, shall comply with the relevant provisions of the current national standard GB 50201 Standard for flood control and of DL 5180 Classification and design safety standard for hydropower projects.

3.0.3 For floods exceeding the design standard for energy dissipation and erosion control, local damage to the energy dissipation and erosion control structures is permitted provided that it is easy to repair; such damage shall not endanger the dam and the other main structures, shall not affect the normal operation of the project, and shall satisfy the following requirements.

3.0.3 Item 1 — when damage to the energy dissipation and erosion control structures would affect the safety of the dam and of the other main structures, the check flood standard for energy dissipation and erosion control shall be studied and may be determined through demonstration on the basis of the layout of the project and of the degree of influence of the flood discharge on the safety of the structures of the project.

3.0.3 Item 2 — when instability of the water retaining structures may be caused, the check shall be made with the check flood standard of the water retaining structures.

3.0.4 The design of the spillway shall take into account frequently occurring floods lower than the design flood standard for energy dissipation and erosion control, discharge at small flow rates, and the unfavourable situations that may arise during the construction period and during early operation. The standard for frequently occurring floods may be chosen between the 2-year and the 20-year flood according to the natural conditions and the characteristics of the project.

3.0.5 The design of the spillway shall determine the mode of operation of the spillway and the mode of opening and closing of the gates in accordance with the flood control dispatching requirements of the project, and operating rules shall be drawn up. For large projects, a dispatching plan for the opening and closing of the gates during the construction period shall be prepared.

3.0.6 The reasonable service life of the spillway shall comply with the relevant provisions of the current national standard GB 50199 Unified standard for reliability design of hydraulic engineering structures and of NB/T 10857 Code for design of reasonable service life and durability of hydropower projects.

3.0.7 The hydraulic design of the spillway shall include hydraulic model tests and numerical analysis carried out in accordance with the requirements set out in the enumerated items of this clause, which continue on the following page of the printed code.