NB/T 35090-2016Design code for underground powerhouses of hydropower stations (English PDF)

Foreword

This document was issued on 5 December 2016 by the National Energy Administration of the PRC and takes effect on 1 May 2017.

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.

This code has been compiled by the drafting group in accordance with the requirements of the Notice of the National Energy Administration on the issuance of the second batch of the 2012 plan for the formulation (revision) of industry standards in the energy field (Guo Neng Ke Ji [2012] No. 326), on the basis of extensive investigation and research, careful summing-up of engineering practice and wide solicitation of opinions.

The main technical contents of this code are: layout of the underground powerhouse; stability analysis of the surrounding rockmass; excavation and support design of the surrounding rockmass; feedback analysis of surrounding rockmass stability and dynamic design during the construction period; structural design of the underground powerhouse; design of seepage control, drainage and moistureproofing; and design of safety monitoring.

This code is placed under the administration of the National Energy Administration. It was proposed by, and is under the day-to-day management of, the General Institute of Hydropower and Water Resources Planning and Design, while the Standardization Technical Committee for Hydropower Survey and Design of the Energy Industry is responsible for the interpretation of its specific technical contents.

Comments and suggestions arising during the implementation of this code should be sent to the General Institute of Hydropower and Water Resources Planning and Design, No. 2 Liupukang Beixiaojie, Xicheng District, Beijing, postcode 100120.

Chief compiling organization of this code: Powerchina Chengdu Engineering Corporation Limited (China Power Construction Group Chengdu Survey, Design and Research Institute Co., Ltd.).

Main drafters of this code: Wang Renkun, Xiao Pingxi, Zhang Yong, Zhao Xiaofeng, Fan Xianglun, Liao Chenggang, Chen Xugao, Hu Xiaowen, Peng Weiwei, Zhang Luobin, Zhang Shunli, Hou Pan, Xing Wanbo, Cheng Lijuan, Xin Xianglin, Hou Dongqi, Gong Shaohong, Zhang Enbao.

Main reviewers of this code: Dang Lincai, Sun Baoping, Hu Bin, Fan Fuping, Lu Mingzhi, Fang Guangda, Wang Yuansheng, Li Guangshun, Li Yi, Ning Huawan, Yang Yiwen, Li Kaide, Yang Yunsheng, Ying Heping, Zhang Manman, Hao Jungang, Zhang Xiaosong, Wen Xuejun, Piao Ling, Li Shisheng.

Publication and approval data

Standard designation: NB/T 35090-2016, an industry standard of the energy sector of the People's Republic of China, issued by the National Energy Administration.

Classification data printed on the cover: ICS 27.140; China Standard Classification Code P 59; filing (record) number J2304-2017.

Date of issue: 5 December 2016. Date of implementation: 1 May 2017.

Chief compiling department: General Institute of Hydropower and Water Resources Planning and Design. Approving department: National Energy Administration. Date of entry into force: 1 May 2017.

Published and distributed by China Electric Power Press, No. 19 Beijing Zhan Xijie, Dongcheng District, Beijing, postcode 100005; printed by Beijing Chuanqijia Colour Printing Co., Ltd.

Printing data: first edition May 2017, first Beijing printing May 2017; format 850 mm by 1168 mm, 32-mo, 2.875 printed sheets, 68 thousand characters; print run 001 to 300 copies.

Book number 155198-84; list price 24.00 yuan. All rights reserved; infringement will be prosecuted.

Approval instrument: Announcement of the National Energy Administration No. 9 of 2016, dated 5 December 2016, by which 373 industry standards were approved, among them 66 energy standards (NB), 29 energy and petrochemical standards (NB/SH), 111 electric power standards (DL) and 167 petroleum standards (SY). In the annexed catalogue of industry standards this code appears as item 44, NB/T 35090-2016, Design code for underground powerhouses of hydropower stations, with approval date 2016-12-05 and implementation date 2017-05-01; the column for the superseded standard is blank, so this code replaces no earlier document.

Structure of the code

The following chapters and clauses complete the body of the code; their titles are reproduced from the official English Contents printed in the standard.

3.2 Interior arrangement of powerhouse, page 10.

4 Surrounding rockmass stability analysis, page 13.

4.1 General requirement, page 13.

4.2 Regression of in-situ stress, page 14.

4.3 Numerical analysis of surrounding rockmass stability, page 15.

4.4 Block stability analysis, page 16.

5 Excavation and support design of surrounding rockmass, page 22.

5.1 General requirement, page 22.

5.2 Excavation design, page 23.

5.3 Shotcrete support, page 23.

5.4 Anchor bar support, page 24.

5.5 Tendon support, page 25.

5.6 Concrete lining, page 26.

5.7 Excavation and support of special geological conditions and parts, page 26.

6 Feedback analysis of surrounding rockmass stability and dynamic design in construction period, page 28.

7 Structural design of underground powerhouse, page 30.

7.1 General requirement, page 30.

7.2 Structural design, page 30.

7.3 Detailing requirements, page 32.

8 Design of seepage control and drainage and moistureproof, page 33.

8.1 General requirement, page 33.

8.2 Anti-seepage curtain design, page 33.

8.3 Drainage curtain design of powerhouse area, page 34.

8.4 Drainage design of powerhouse, page 34.

8.5 Waterproof and moisture proof design, page 35.

9 Design of safety monitoring, page 36.

9.1 General requirement, page 36.

9.2 Monitoring design, page 36.

9.3 Data collection and analysis, page 37.

Explanation of wording in the code, page 39.

List of normative standards, page 40.

Addition: Explanation of provisions, page 41.

1 Scope

NB/T 35090-2016 is the Chinese design code for the underground powerhouses of hydropower stations. Putting the machine hall inside the mountain avoids the constraints of a narrow gorge and shortens the waterway, but it creates a very large cavern in rock that must stay stable for the life of the station, with a second cavern for the transformers beside it and a web of access, cable, drainage and ventilation tunnels around them. The code sets the general provisions and defined terms, then the requirements for siting the cavern complex against the rock mass quality, the in-situ stress field, the geological structure and the groundwater. Layout follows: the arrangement and spacing of the main powerhouse, transformer cavern and surge chamber, their axis orientation relative to the principal stress and to the dominant joint sets, and the network of tunnels and shafts that serve them. Excavation and support are treated together - the sequence of benching, the shotcrete, bolting, cable anchors and concrete lining, and the monitoring that confirms the rock is behaving as predicted. The structural design of the powerhouse inside the cavern, the crane beams and their rock anchors, the machine foundations, and the floors and galleries follow. Waterproofing and drainage, ventilation and air conditioning, fire protection and escape routes, lighting, and the moisture-proofing that an underground plant needs complete the code. It applies to underground hydropower stations in China.

1.0.1 This code is formulated in order to standardize the design of underground powerhouses of hydropower stations, to ensure design quality and to achieve safety and reliability, economic rationality, technical advancement, environmental friendliness and conservation of resources.

1.0.2 This code is applicable to the design of grade 1, grade 2 and grade 3 underground powerhouses of newly built, reconstructed and extended hydropower stations. It may also be used for grade 4 and grade 5 underground powerhouses.

1.0.3 New technologies and new materials should be reasonably adopted in the design of underground powerhouses, and energy-saving and environment-friendly materials should be actively adopted.

1.0.4 The design of underground powerhouses shall comply with the relevant provisions of the current industry standard Design code for powerhouse of hydropower station, NB 35011.

1.0.5 In addition to complying with this code, the design of underground powerhouses of hydropower stations shall also comply with the provisions of the current relevant national standards.

2 Terms

2.0.1 Underground powerhouse. The powerhouse of a hydropower station built in a chamber below the ground surface.

2.0.2 Main powerhouse chambers. The chambers in which the hydro-generating units and their auxiliary equipment are installed and which are used for power generation operation and for erection and maintenance work.

2.0.3 Main transformer chambers. The chambers in which the main transformers and their ancillary equipment are installed.

2.0.4 Main underground chambers. Those chambers of the underground powerhouse chamber group that are comparatively large in dimensions and highly interrelated with one another, mainly meaning large chambers such as the main powerhouse chamber, the main transformer chamber and the tailrace surge chamber.

2.0.5 Appurtenant chambers and tunnels. All the chambers and tunnels of the underground powerhouse chamber group other than the main chambers, such as access traffic tunnels, ventilation tunnels, drainage tunnels and connecting tunnels.

2.0.6 Flexible support. A support measure composed of shotcrete, anchor bars, tendons and other members of comparatively low rigidity, which allows the surrounding rockmass a certain amount of deformation so that its self-bearing capacity can be brought into effective play.

2.0.7 Initial support. Where the permanent support of a chamber is carried out in stages, the support applied at an early stage after the excavation of the chamber, the main function of which is to ensure the stability of the surrounding rockmass during the construction period.

2.0.8 Secondary support. The support applied again after the initial support, according to the stability condition of the surrounding rockmass or the requirements of long-term operation.

2.0.9 Systematical bolt or tendon. A group of anchor bars or tendons arranged regularly around the periphery of a chamber at a certain spacing and row spacing, in order to satisfy the overall stability of the surrounding rockmass.

2.0.10 Design bearing capacity. The design value of the resistance that a tendon shall possess in order to resist the load.

2.0.11 Ratio of rock strength to in-situ stress. The ratio of the saturated uniaxial compressive strength of the rock to the magnitude of the maximum principal stress of the surrounding rockmass at the location of the main chambers.

3 Layout of underground powerhouse - Arrangement of powerhouse area

3.1.1 The location of the underground powerhouse shall take into account such main factors as the topographic and geological conditions, the arrangement of the project complex, the hydraulic conditions of the water conveyance system, the construction conditions, the arrangement of the electromechanical equipment, the operating requirements and environmental protection, and a head-type, intermediate-type or tail-type arrangement shall be adopted on the basis of technical and economic comparison.

3.1.2 The layout of the underground powerhouse shall follow the principles listed below.

3.1.2 item 1. The layout of the underground powerhouse shall be coordinated with the overall layout of the project complex and shall suit the topographic and geological conditions of its location, satisfying the requirements of equipment arrangement, production operation, resource conservation and energy saving and environmental protection.

3.1.2 item 2. The layout of the chamber group should follow the principles of combining the underground works with the surface works, combining the temporary works with the permanent works, and using one chamber for several purposes.

3.1.2 item 3. The main chambers should be located in a ground section where the geological structure is simple, the rockmass is comparatively intact, the thickness of the overlying rock stratum is suitable, groundwater is not developed and the bank slope is stable; large faults, zones of high in-situ stress and zones of developed joints and fissures should be avoided. Where they cannot be avoided, a dedicated technical demonstration shall be carried out.

3.1.2 item 4. Where the design seismic intensity of the site is intensity 8 or above, a cave-type powerhouse should not be built in a mountain body with steep topography, weathered rockmass or developed geological structures.

3.1.2 item 5. An underground powerhouse should not be built in a zone of extremely high in-situ stress where the ratio of rock strength to in-situ stress is less than 2.5.

3.1.2 item 6. The underground powerhouse should not be arranged in an area appreciably affected by the transmission of dam loads; where this is difficult to avoid completely, it shall be determined through dedicated analysis and demonstration.

3.1.2 item 7. The position of the tunnel portals at the ground surface should be selected in a ground section where the bedrock is exposed, the bank slope is stable, the terrain is relatively gentle and construction and external traffic are convenient, and the influence of flood water and of the spray from flood discharge shall be taken into account; ground sections affected by landslides, collapses and deformation bodies and other unfavourable geological conditions, and areas affected by debris flow, shall be avoided.