NB/T 10391-2020Code for design of hydraulic tunnel (English PDF)

Foreword

This document was issued on 23 October 2020 by the National Energy Administration of the PRC and takes effect on 1 February 2021.

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It replaces DL/T 5195-2004, which is superseded.

This code has been revised by the drafting group in accordance with the requirements of the Notice of the National Energy Administration on Issuing the Second Batch of Plans for Formulation and Revision of Industry Standards in the Energy Field in 2014 (Guo Neng Ke Ji [2015] No. 12), on the basis of extensive investigation and research, careful summarization of practical experience and wide solicitation of opinions.

The main technical contents of this code are: general provisions, terms, basic requirements, tunnel layout, shape and size of cross section, hydraulic design, unlined tunnel and anchor-shotcrete tunnel, basic principles for structural design, concrete and reinforced concrete lining, prestressed concrete lining, high pressure bifurcation tunnel with reinforced concrete lining, design for machine bored tunnel, design for special rock mass and poor geological tunnel, plugging body design, grouting and seepage control and drainage, safety monitoring, and operation and maintenance.

The main technical contents revised in this code are as follows.

Added the design of high pressure reinforced concrete lining tunnels, the design of machine bored tunnels, and the design of tunnel sections in special rock masses and poor geological conditions.

Added the technical requirements related to water filling and emptying of power generation tunnels.

Added the contents on discharge capacity, aerated water depth, external water pressure, and stress calculation of circular tunnel lining bearing uniform external water load.

Added design situations such as the tunnel construction period, the maintenance period and the operation period of the discharge tunnel, and added the action of backfill grouting pressure together with its partial factor.

Added the seepage stability requirements for the design of the plugging body.

Revised the relevant contents concerning the layout and the hydraulic design of high flow velocity hydraulic tunnels.

Revised the expression for the stability calculation of surrounding rock blocks, changing the partial factor expression into a safety factor expression.

Deleted from the original code Appendix A engineering geological classification of surrounding rock, Appendix B materials, Appendix F types and parameters of anchor-shotcrete support, and Appendix I calculation of circular free-flow tunnel lining and non-circular tunnel lining; the contents of Appendix D and Appendix E of the original code have been incorporated into the body text.

Integrated the contents of Appendix J of the original code, concrete lining cracks and measures for their prevention, into the relevant provisions.

This code is under the administration of the National Energy Administration; it is proposed by and under the routine administration of the China Renewable Energy Engineering Institute, and the specific technical contents are interpreted by the Energy Industry Standardization Technical Committee for Hydropower Survey and Design. Comments and suggestions arising in the course of implementation should be sent to the China Renewable Energy Engineering Institute, No. 2 Liupukang Beixiaojie, Xicheng District, Beijing, postcode 100120.

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

Participating development organizations of this code: PowerChina Huadong Engineering Corporation Limited; PowerChina Northwest Engineering Corporation Limited; PowerChina Zhongnan Engineering Corporation Limited.

Chief drafters of this code: Huang Yankun, Yang Huaide, Hao Yuanlin, Liu Yue, You Xiang, Xie Jinyuan, Liu Yuan, Zhang Yang, Liu Changgui, Liu Lijuan, Du Zhenyu, Chen Xiangrong, Yi Bo, Zhao Lu, Li Yun, Chen Xugao, Ju Lin.

Chief reviewers of this code: Dang Lincai, Hao Jungang, Zeng Xionghui, Liu Shanjun, Wang Jianhua, Wang Kangzhu, Tian Zhenghai, Ning Huawan, Li Linian, Chen Lifen, Wang Ke, Xiong Chungeng, Li Yun, Yang Xiaolong, Chen Wenhua, Du Xiaokai, Zheng Linping, He Shuangxi.

Structure of the code

Chapter 4 Tunnel Layout, beginning on page 6, is organized in three sections: 4.1 Tunnel Line Selection, 4.2 Tunnel Inlet and Outlet Layout, and 4.3 Multipurpose Tunnel.

Chapter 5 Shape and Size of Cross Section, beginning on page 12, is organized in three sections: 5.1 General Requirements, 5.2 Cross Section Shape, and 5.3 Cross Section Size.

Chapter 6 Hydraulic Design, beginning on page 15, is organized in two sections: 6.1 Principles for Hydraulic Calculation, and 6.2 Design of Cavitation Erosion Control for Water Boundary with High Flow.

Chapter 7 Unlined Tunnel and Anchor-Shotcrete Tunnel, beginning on page 19, is organized in five sections: 7.1 General Requirements, 7.2 Shotcrete Support, 7.3 Anchor Bolt Support, 7.4 Anchor-Shotcrete Support with Mesh, and 7.5 Combined Support.

Chapter 8 Basic Principles for Structural Design occupies page 25 and is presented without subdivision into sections.

Chapter 9 Concrete and Reinforced Concrete Lining, beginning on page 26, is organized in four sections: 9.1 General Requirements, 9.2 Action and Combination of Action Effects, 9.3 Lining Calculation, and 9.4 Lining Joint.

Chapter 10 Prestressed Concrete Lining, beginning on page 32, is organized in three sections: 10.1 General Requirements, 10.2 Grouting-Type Prestressed Concrete Lining, and 10.3 Circular Anchored Prestressed Concrete Lining.

Chapter 11 High Pressure Bifurcation Tunnel with Reinforced Concrete Lining begins on page 34 and is presented without subdivision into sections.

Chapter 12 Design for Machine Bored Tunnel begins on page 35 and is presented without subdivision into sections.

Chapter 13 Design for Special Rock Mass and Poor Geological Tunnel begins on page 37 and is presented without subdivision into sections.

Chapter 14 Plugging Body Design, beginning on page 41, is organized in three sections: 14.1 General Requirements, 14.2 Design and Calculation, and 14.3 Structural Requirements.

Chapter 15 Grouting and Seepage Control and Drainage, beginning on page 44, is organized in two sections: 15.1 Grouting, and 15.2 Seepage Control and Drainage.

Chapter 16 Safety Monitoring, beginning on page 46, is organized in two sections: 16.1 General Requirements, and 16.2 Monitoring Items and Requirements.

Chapter 17 Operation and Maintenance begins on page 48 and is presented without subdivision into sections.

Appendix A Head Loss Calculation begins on page 50 and is the most extensive appendix of the code.

Appendix B Calculation of Discharge Capacity for Hydraulic Tunnel with Pressure Inlet begins on page 59.

Appendix C Aeration Water Depth Calculation begins on page 61.

Appendix D Calculation of Circular Pressure Tunnel Lining begins on page 63.

Appendix E Calculation of External Water Pressure of Tunnel Concrete Lining begins on page 72.

Appendix F Stress Calculation of Circular Tunnel Lining under Uniform External Water Pressure begins on page 74.

The code closes with the Explanation of Wording in This Code on page 75, the List of Quoted Standards on page 76, and the Addition: Explanation of Provisions on page 77.

1 Scope

NB/T 10391-2020 is the Chinese design code for hydraulic tunnels, replacing DL/T 5195-2004. It governs the tunnels that carry water through rock on hydropower and water resources projects - diversion and headrace tunnels, tailrace and spillway tunnels, bottom outlets and flood discharge tunnels - whether they run free-surface or under pressure. The code opens with general provisions and a full set of defined terms, then sets the basic requirements: the class of the tunnel, the design and check flood standards, the service life and the safety factors that follow. Alignment and profile selection come next, with the geological investigation the choice depends on and the treatment of unfavourable ground. The hydraulic design covers flow capacity, free-surface and pressurised flow, air entrainment and aeration, cavitation and the surface finish needed to avoid it, energy dissipation at the outlet, and the transient analysis of surge and water hammer where a tunnel serves a power station. Structural design follows: the rock load and the external and internal water pressures, the design of unlined, shotcrete-lined and concrete-lined sections, reinforced and prestressed linings, steel lining where internal pressure demands it, and the grouting for consolidation and backfill. Construction requirements, drainage, the inlet and outlet structures and their gates, and the monitoring and inspection expected in service complete the document. It applies to the feasibility, preliminary and detailed design stages of hydraulic tunnels in China.

1.0.1 This code is formulated in order to standardize the design of hydraulic tunnels and to make such design safe and reliable, technically advanced and economically rational.

1.0.2 This code is applicable to the design of hydraulic tunnels of newly built, reconstructed and extended hydropower projects.

1.0.3 The grade of a hydraulic tunnel shall be determined in accordance with the relevant provisions of the current national standards Standard for Flood Control GB 50201 and Standard for Classification and Design Safety of Hydropower Projects DL 5180.

1.0.4 The design of a hydraulic tunnel shall make full use of the self-stabilizing capacity, the bearing capacity and the seepage resistance capacity of the surrounding rock.

1.0.5 For a pressure hydraulic tunnel with steel plate lining, the structural design shall be carried out in accordance with the relevant provisions of the current industry standard Design Code for Penstocks of Hydropower Stations NB/T 35056.

1.0.6 The design of a hydraulic tunnel shall satisfy the requirements of the overall planning of the project and of environmental protection.

1.0.7 In addition to this code, the design of hydraulic tunnels shall also comply with the provisions of the relevant current national standards.

2 Terms

2.0.1 hydraulic tunnel - A water passage with a closed cross section, excavated in a mountain body or underground in a hydropower or water conservancy project and used for water conveyance, power generation, irrigation, flood discharge, river diversion, emptying, sediment flushing and similar purposes.

2.0.2 pressure tunnel - A hydraulic tunnel in which the flow fills the whole section and the perimeter of the tunnel wall is subjected to the action of water pressure.

2.0.3 free-flow tunnel - A hydraulic tunnel in which the flow inside the tunnel has a free water surface.

2.0.4 high pressure tunnel - A tunnel in which the internal pressure head is not less than 100 m.

2.0.5 high flow velocity tunnel - A tunnel in which the flow velocity inside the tunnel is greater than 20 m/s.

2.0.6 tunnel support - Engineering measures that reinforce the surrounding rock of a tunnel by means of structures or members and other materials.

2.0.7 anchor-shotcrete support - Engineering measures that reinforce the rock mass by means of anchor bolts and shotcrete.

2.0.8 primary support - The support carried out immediately after the excavation of the underground opening.

2.0.9 secondary support - A further support carried out after the primary support, decided according to the monitoring results or to the service function.

2.0.10 random anchor bolt - Anchor bolts arranged locally in the surrounding rock in order to prevent collapse or sliding of the rock mass.

2.0.11 systematic anchor bolt - Anchor bolts arranged regularly over the whole excavation face with a certain spacing and row spacing, according to the stability requirements of the surrounding rock.

2.0.12 preset anchor bolt - Anchor bolts set in advance in the surrounding rock at the working face of the opening being excavated, for the stability of the next excavation section.

2.0.13 lining - Engineering measures in underground works that use materials such as concrete and reinforced concrete for support, in order to reinforce the surrounding rock or to make the water passage surface smooth.

2.0.14 backfill grouting - Grouting measures that fill with grout the voids and cavities between the concrete lining and the surrounding rock, in order to increase the compactness of the surrounding rock or of the structure.

2.0.15 joint grouting - Grouting measures that inject grout into the joint surfaces between concrete blocks through embedded pipelines or by other means, in order to strengthen the integrity of the structure and to improve the force transmission conditions.

2.0.16 contact grouting - Grouting measures that inject grout into the gap between the concrete and the bedrock through embedded pipelines or by other means, in order to strengthen the bonding capacity of the contact surface.

2.0.17 consolidation grouting - Grouting measures that reinforce with grout the surrounding rock having geological defects such as fissures or fractured zones, in order to strengthen its integrity, raise its bearing capacity and reduce leakage.

2.0.18 hydraulic fracturing - General term for the physical phenomena in which the pressurized water in a hydraulic tunnel drives the existing fissures and pores in the rock mass to expand, to extend and to become interconnected.

2.0.19 machine bored tunnel - A boring machine is a new and advanced type of tunnel construction machinery which excavates by means of rotary cutting tools, breaking at the same time the surrounding rock or the overburden inside the tunnel and advancing so as to form the whole tunnel section; a tunnel driven by means of a boring machine is called a machine bored tunnel.

2.0.20 cavitation - The process of formation, development and collapse of vapour or gas bubbles inside a liquid or at the liquid-solid interface, occurring when the local pressure inside the liquid drops to the saturated vapour pressure of the liquid.

2.0.21 cavitation erosion - The erosion and damage of a solid boundary caused by cavitation.

2.0.22 rock burst - The phenomenon in which the elastic deformation potential energy accumulated in the rock mass is released suddenly and violently under certain conditions, causing the rock to burst and to be ejected.

3 Basic requirements

3.0.1 According to the layout of the project complex, the function of the tunnel and the requirements of the different design stages, the design of a hydraulic tunnel shall collect data concerning hydrology, sediment, power economy, topography, geology, earthquake, ecological environment, soil and water conservation, construction conditions, metal structures, electromechanical equipment, building materials, mode of operation and similar aspects.

3.0.2 The geological investigation of the tunnel inlet and outlet and along the tunnel line shall be carried out in accordance with the relevant provisions of the current national standard Code for Hydropower Engineering Geological Investigation GB 50287, according to the degree of complexity of the topographic and geological conditions, the grade of the tunnel and the different design stages. For grade 1 high pressure hydraulic tunnels and high pressure concrete bifurcation tunnels, representative sections shall be selected in the field for tests such as in-situ stress measurement and hydraulic fracturing.

3.0.3 In the preliminary design stages the following basic geological data shall be collected for a hydraulic tunnel:

3.0.3 item 1 The characteristics of the surrounding rock, the geological structures and the in-situ stress along the tunnel line.

3.0.3 item 2 The karst and the hydrogeology along the tunnel line.

3.0.3 item 3 The stability of the tunnel inlet and outlet and of the related slopes.

3.0.3 item 4 Geological phenomena affecting the safety of the tunnel, such as karst caves, water inrush, rock burst, high ground temperature, harmful gases and radioactive substances.

3.0.4 During the excavation of a hydraulic tunnel, geological logging shall be carried out in due time according to the actual situation, geological data shall be collected and checked, and geological forecasting shall be provided for the construction. For tunnel sections with complex geological conditions, methods such as pilot tunnels, advance drilling and advance geophysical prospecting should be adopted during construction in order to ascertain the geological conditions.

3.0.5 The classification of the surrounding rock of a hydraulic tunnel shall comply with the relevant provisions of the current national standard Code for Hydropower Engineering Geological Investigation GB 50287.

3.0.6 The parameters of the materials used in the design of a hydraulic tunnel, such as shotcrete, anchor bolts, concrete and reinforcement, shall comply with the relevant provisions of the current national standards Technical Code for Engineering of Ground Anchorages and Shotcrete Support GB 50086 and Design Specification for Hydraulic Concrete Structures DL/T 5057.

3.0.7 A stone collecting pit should be provided in a long water conveyance power generation tunnel.