NB/T 10241-2019Specification for engineering geological investigation of underground structures for hydropower projects (English PDF)

Foreword

This document was issued on 4 November 2019 by the National Energy Administration of the PRC and takes effect on 1 May 2020.

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It replaces DL/T 5415-2009, which is superseded.

This specification has been revised by the drafting group in accordance with the requirements of the Notice of the National Energy Administration on Issuing the 2015 Plan for the Formulation and Revision of Standards in the Energy Sector (Guo Neng Ke Ji [2015] No. 283), on the basis of extensive investigation and research, a careful summary of practical experience, and wide solicitation of comments.

The main technical contents of this specification are: basic requirements; the content of engineering geological investigation of underground structures; the methods of engineering geological investigation of underground structures; the engineering geological assessment of the surrounding rock of underground structures; and the geology of underground structures during construction.

The main technical contents revised in this specification are the following.

Content on environmental protection during investigation work has been added.

Content on ground temperature investigation and on the investigation of water inrush and mud inrush has been added.

Content on the prediction of mud inrush in fault fracture zones with a relatively high mud content has been added.

Content on the assessment of heat hazard due to ground temperature has been added.

Content on the engineering geological assessment of the stability of the surrounding rock of air cushion surge chambers has been added.

The content of the part dealing with the geology of underground structures during construction has been adjusted: the contents of geological work for surrounding rock treatment and of geological work for surrounding rock monitoring have been simplified and merged into geological work during construction.

The content of the part dealing with the classification of gas tunnels has been adjusted.

This specification is under the administration of the National Energy Administration. The Hydropower and Water Resources Planning and Design General Institute has put it forward and is responsible for its routine management, and the Standardization Technical Committee for Hydropower Investigation and Design of the Energy Sector is responsible for the interpretation of its specific technical content.

Should any comment or suggestion arise in the course of implementation, it is requested that it be sent to the Hydropower and Water Resources Planning and Design General Institute, at No. 2 Liupukang Beixiaojie, Xicheng District, Beijing, postcode 100120.

The chief editing organization of this specification is PowerChina Chengdu Engineering Corporation Limited, that is, the Chengdu Engineering Investigation, Design and Research Institute of the China Power Construction Group.

The chief drafters of this specification are: Li Wengang, Chen Weidong, Liao Mingliang, Yang Jianhong, Deng Zhongwen, Li Panfeng, Zhang Yunda, Sha Chun, Zhang Yong and Ju Lin.

The chief reviewers of this specification are: Yang Jian, Wan Zongli, Zhang Dongsheng, Guo Yihua, Mi Yingzhong, Gong Hailing, Shan Zhigang, Chen Liqiang, Lu Dongliang, Zeng Xiangxi, Zhang Guofu, Li Kaide, Gao Qiang, Wu Yongfeng, Dai Qixiang, Wang Huiming and Li Shisheng.

The foreword therefore identifies a single chief editing organization, ten chief drafters and seventeen chief reviewers, a composition typical of a hydropower sector specification revised from an earlier electric power standard.

Publication and Approval Data

NB/T 10241-2019 is an energy sector standard of the People's Republic of China (Zhonghua Renmin Gongheguo Nengyuan Hangye Biaozhun). It is registered under ICS 27.140 (hydraulic energy engineering) and under the Chinese Standard Classification Code P 59, and it carries the sector prefix NB together with the professional classification letter P shown on the cover.

The Chinese title printed on the cover is Shuidian Gongcheng Dixia Jianzhuwu Gongcheng Dizhi Kancha Guicheng. The official English title printed on the cover is Specification for Engineering Geological Investigation of Underground Structures for Hydropower Projects.

The standard was issued on 4 November 2019 and came into force on 1 May 2020, giving a transition period of just under six months between issue and implementation.

The standard replaces DL/T 5415-2009, the earlier electric power sector specification covering the same subject. With the publication of NB/T 10241-2019 the superseded document ceased to apply on the implementation date.

The issuing authority is the National Energy Administration (Guojia Nengyuanju), whose name appears at the foot of the cover page above the word Fabu (issued).

The title page states that the chief editing department is the China Renewable Energy Engineering Institute, also known as the Hydropower and Water Resources Planning and Design General Institute; the approving department is the National Energy Administration; and the date of entry into force is 1 May 2020. The printed edition is dated 2020 and was published in Beijing.

The standard was promulgated by Announcement No. 6 of 2019 of the National Energy Administration, dated 4 November 2019. That announcement approved 384 energy sector standards headed by the Technical Specification for Electrical Prospecting of Hydropower Projects (Attachment 1), 48 English versions of energy sector standards headed by the Technical Guide for Rock-Filled Concrete Dams (Attachment 2), first amendment sheets for 7 energy sector standards headed by the Technical Code for Environmental Impact Assessment of Wind Farm Projects (Attachment 3), and the abolition of 5 energy sector standards and standard projects headed by the Charging Standard for Investigation and Design of Wind Farm Projects (Attachment 4).

The four attachments to the announcement are: 1. Catalogue of Sector Standards; 2. Catalogue of English Versions of Sector Standards; 3. Notification Sheets of Amendments to Sector Standards; 4. Catalogue of Abolished Sector Standards and Standard Projects.

In the Catalogue of Sector Standards (Attachment 1) this document appears as serial number 18, with standard number NB/T 10241-2019, title Shuidian Gongcheng Dixia Jianzhuwu Gongcheng Dizhi Kancha Guicheng, superseded standard DL/T 5415-2009, approval date 2019-11-04 and implementation date 2020-05-01. No adopted international standard number is shown, so the document is a wholly domestic specification and not an adoption of an ISO or IEC text.

The front matter of the printed edition is paginated with Roman numerals I to VIII and carries, in order, the announcement of the National Energy Administration, the extract from the catalogue of sector standards, the Chinese foreword, the Chinese table of contents and the official English Contents. The body of the specification is paginated with Arabic numerals from page 1 to page 39 or beyond.

Structure of the Document

The official English Contents printed in the front matter shows a body text of seven clauses followed by seven appendices and three items of back matter, occupying pages 1 to 39 and beyond.

Clause 1, General Provisions, occupies page 1. Clause 2, Terms, occupies page 2. Clause 3, Basic Requirements, occupies page 3.

Clause 4, Engineering Geological Investigation Content for Underground Structures, begins on page 4 and is divided into 4.1 Investigation of Basic Geological Conditions, page 4, and 4.2 Investigation of Engineering Geological Properties, page 7.

Clause 5, Engineering Geological Investigation Methods for Underground Structures, begins on page 10 and is divided into 5.1 Engineering Geological Investigation Methods for Tunnels, page 10, and 5.2 Engineering Geological Investigation Methods for Underground Powerhouse System, page 12.

Clause 6, Engineering Geological Assessment of Surrounding Rock for Underground Structures, begins on page 15 and is the longest clause of the specification. It comprises 6.1 Location Selection for Underground Structures, page 15; 6.2 Surrounding Rock Classification and Engineering Geological Assessment on Stability of Surrounding Rock, page 16; 6.3 Prediction of Rock Burst, page 18; 6.4 Prediction of Water Inrush and Mud Inrush, page 19; 6.5 Prediction of Ground Temperature, Harmful Gases and Radioactivity, page 20; 6.6 Prediction of External Water Pressure, page 21; 6.7 Engineering Geological Assessment on Stability of Surrounding Rock for High Head Pressure Tunnels, page 21; and 6.8 Engineering Geological Assessment on Stability of Surrounding Rock for Air Cushion Surge Chambers, page 22.

Clause 7, Engineering Geological Investigation During Underground Structure Construction, begins on page 24 and comprises 7.1 Investigation of Special Engineering Geological Problems, page 24, and 7.2 Geological Work During Construction, page 24.

Appendix A, Determination of Firmness Coefficient, Unit Elastic Resistance Coefficient and Strength-Stress Ratio of Surrounding Rock, begins on page 27.

Appendix B, Types of Soluble Halite, begins on page 29, and Appendix C, Determination of Physical and Mechanical Parameters of Surrounding Rock, begins on page 30. The Chinese heading of Appendix C refers to empirical values of the main physical and mechanical parameters of the several classes of surrounding rock.

Appendix D, Instability Mechanism Types and Failure Modes of Surrounding Rock, begins on page 31, and Appendix E, Allowable Relative Convergence Values for Tunnels or Caverns, begins on page 32.

Appendix F, Maximum Allowable Concentration of Harmful Gases and Main Indexes of Air Composition for Underground Caverns, begins on page 33, and Appendix G, Classification of Gas Tunnel, begins on page 34. Appendix G corresponds to the part on the classification of gas tunnels whose content was adjusted in this revision.

The back matter consists of Explanation of Wording in This Specification, page 36; List of Quoted Standards, page 37; and Addition: Explanation of Provisions, page 39, the last being the separately paginated commentary that accompanies Chinese design and investigation codes.

The standards quoted within the readable extract are the national standard GB 50287, Code for Hydropower Engineering Geological Investigation, cited three times, and the sector standards NB/T 35098, on regional tectonic stability investigation of hydropower projects, and NB/T 10075, on engineering geological investigation of karst for hydropower projects.

1 Scope

NB/T 10241-2019 governs the engineering geological investigation of underground structures on hydropower projects, replacing DL/T 5415-2009. Underground here means the powerhouse and transformer caverns, the headrace and tailrace tunnels, the surge chambers and shafts, the diversion and access tunnels, and the spillway tunnels - works whose behaviour is decided almost entirely by the rock they are cut into, and where getting the ground model wrong is expensive in a way that cannot be corrected later. The specification sets the general provisions and the defined terms, then the scope, methods and depth of investigation at each design stage, from planning through feasibility to detailed design and construction. It covers the surface mapping, the geophysical exploration, the drilling and the exploratory adits, the in-situ stress measurement and the rock mechanics testing both in situ and in the laboratory, and the hydrogeological work. It then sets out the assessment: the rock mass classification used underground, the stability of the cavern roof and walls and the wedges formed by the joint sets, the assessment of rockburst under high stress and of large deformation in weak rock, the water inrush and gas hazards, the treatment of faults and weak zones crossing the excavation, and the surrounding rock parameters supplied to the designer. Investigation during construction and the report close the document.

Clause 1 of the specification sets out the general provisions in three articles, numbered 1.0.1 to 1.0.3 in the four-level numbering system used for Chinese design and investigation codes.

1.0.1 This specification is formulated in order to standardize the content, the methods, the assessment and the technical requirements of the engineering geological investigation of underground structures of hydropower projects, and to ensure the quality of that engineering geological investigation.

1.0.2 This specification is applicable to the engineering geological investigation of underground structures of large hydropower projects. This specification is not applicable to the engineering geological investigation of underground structures of medium and small hydropower projects.

1.0.3 In addition to complying with this specification, the engineering geological investigation of underground structures of hydropower projects shall also comply with the provisions of the relevant current national standards.

2 Terms

Clause 2 of the specification defines eleven terms, numbered 2.0.1 to 2.0.11. Each term is given in Chinese followed by its English equivalent, and then defined. The English equivalents printed in the standard are reproduced below together with a full translation of each definition.

2.0.1 surrounding rock. The rock mass around an underground cavern in which the stresses are redistributed as a result of excavation, or the rock mass that may have an effect on the stability and deformation of the cavern.

2.0.2 group of caverns. An underground structure system formed by several artificially excavated caverns.

2.0.3 hillside tunnel. A tunnel that passes along one side of a hillslope.

2.0.4 watershed tunnel. A tunnel that passes through a mountain ridge.

2.0.5 rock burst. The dynamic phenomenon in which, when a cavern is excavated under high ground stress conditions, the stress in the surrounding rock is suddenly released, causing rock blocks on the cavern wall to burst and to be ejected.

2.0.6 water inrush. The phenomenon in which, during the construction of an underground cavern, groundwater gushes into or suddenly spurts into the cavern when a water bearing or water permeable rock stratum is crossed.

2.0.7 mud inrush. The phenomenon in which, during the construction of an underground cavern, a sudden and large outflow of mud occurs when a karst cave filled with muddy material, or a section such as a fault fracture zone with a relatively high mud content, is crossed.

2.0.8 high water head tunnel. A tunnel in which the water pressure head inside the tunnel is not less than 100 m.

2.0.9 deep tunnel. A tunnel whose depth of burial is greater than 300 m.

2.0.10 long tunnel. A tunnel whose single bore length is greater than 2000 m.

2.0.11 large-span underground cavern. An underground cavern whose span is greater than 20 m.

The definitions of deep tunnel, long tunnel and large-span underground cavern are purely dimensional thresholds, and they govern which of the more demanding investigation and assessment requirements of the later clauses apply to a given structure.

3 Basic Requirements

Clause 3 of the specification sets out the basic requirements in six articles, numbered 3.0.1 to 3.0.6.

3.0.1 The engineering geological investigation of underground structures shall ascertain the engineering geological conditions of the underground structure area of the hydropower project, shall analyze the engineering geological factors and the engineering geological problems that affect the stability of the surrounding rock of the underground caverns, shall assess the stability of the surrounding rock of the underground caverns, and shall provide the engineering geological data required for the design of the underground structures, for construction excavation and for the support of the surrounding rock.

3.0.2 The engineering geological investigation of underground structures shall follow the design procedure of hydropower projects and shall be carried out progressively and in increasing depth through the planning stage, the pre-feasibility study stage, the feasibility study stage, the tender design stage and the detailed construction drawing design stage. The depth of the work at each investigation stage shall comply with the relevant provisions of the current national standard Code for Hydropower Engineering Geological Investigation, GB 50287.

3.0.3 The engineering geological investigation of underground structures at each stage shall be carried out on the basis of an engineering geological investigation outline.

3.0.4 The engineering geological investigation of underground structures shall be carried out progressively, in combination with the investigation stage and the layout of the structures, following the principles of proceeding from the ground surface to the underground, from general survey to the study of special problems, and from qualitative assessment to quantitative assessment.

3.0.5 All the original data obtained in the course of the investigation work shall be true, accurate and complete, and shall be collated and comprehensively analyzed in a timely manner.

3.0.6 The investigation work shall comply with the relevant requirements of environmental protection.

Article 3.0.6 is one of the additions introduced by this revision; the superseded DL/T 5415-2009 contained no general environmental protection requirement for the investigation work itself.

4 Engineering Geological Investigation Content for Underground Structures

Clause 4 is divided into two subclauses: 4.1, Investigation of Basic Geological Conditions, beginning on page 4 of the body text, and 4.2, Investigation of Engineering Geological Properties, beginning on page 7.

4.1.1 The investigation of the basic geological conditions of the underground structure area shall ascertain the topography and geomorphology, the stratigraphy and lithology, the geological structure, the physical geological phenomena, the karst and the hydrogeological conditions.

4.1.2 The investigation of the topography and geomorphology of the underground structure area shall meet the following requirements.

4.1.2 item 1 The investigation of the topography and geomorphology of the underground structure area shall ascertain the landform types and their genetic types, and shall analyze their relationship with lithology, geological structure and neotectonic movement.

4.1.2 item 2 The investigation of the topography and geomorphology along the tunnel alignment shall ascertain the degree of development of the surface drainage system and of the gullies, the depth of incision, and the variation of the volume of water within the gullies.

4.1.2 item 3 The investigation of the topography and geomorphology of the layout area of the underground powerhouse complex shall ascertain the topographic and geomorphic features, the distribution of the gullies, the depth of incision and the degree of integrity of the terrain.

4.1.3 The investigation of the stratigraphy and lithology of the underground structure area shall meet the following requirements.

4.1.3 item 1 The investigation of magmatic rocks shall ascertain the mineral composition, the chemical composition, the texture, the primary structures and the petrographic features of the rocks, and shall meet the following requirements.

4.1.3 item 1 subitem 1) For intrusive rock bodies and for dyke rocks, the mode of occurrence, the scale of distribution, the contact relationships and the alteration features of the contact zone shall be ascertained.

4.1.3 item 1 subitem 2) For extrusive rocks, the flow structures and their zoning, the eruptive cycles, and the contact relationships with the overlying and underlying strata shall be ascertained.

4.1.3 item 1 subitem 3) The alteration of the magmatic rocks, the eruptive breaks, the rock dykes and their contact relationships shall be the focus of the investigation.

4.1.3 item 2 The investigation of sedimentary rocks shall ascertain the mineral composition, the chemical composition, the texture, the structure, the degree of cementation, the lithological and petrofacies variations, the features of the sedimentary rhythm, the type of formation and the contact relationships of the strata. Weak rock strata, soluble rock types, coal bearing strata, swelling rock types and readily soluble saline rock types distributed in the underground structure area shall be the focus of the investigation.

4.1.3 item 3 The investigation of metamorphic rocks shall ascertain the mineral composition, the chemical composition, the texture, the structure, the degree of metamorphism and the type of metamorphic action of the rocks. Weak strata such as phyllite, slate and schist shall be the focus of the investigation.

4.1.3 item 4 The engineering geological rock groups of the underground structure area shall be subdivided according to the genetic type of the rock, its lithological characteristics, its structural characteristics, the conditions of the bedded assemblage and the physical and mechanical properties of the rock. The degree of detail of the subdivision of the rock groups shall be commensurate with the scale of the engineering geological mapping. Weak interlayers, swelling rock, readily soluble saline rock, and the rock strata that host harmful gases and radioactive minerals may be shown at an enlarged scale.

4.1.3 item 5 In the investigation of the entrance and exit sections of the underground structures, of the shallow buried hillside sections and of the gully crossing sections, the distribution, the genetic type, the thickness, the layered structure and the material composition of the Quaternary cover shall be ascertained.

4.1.4 The investigation of the geological structure of the underground structure area shall comply with the following provisions.

4.1.4 item 1 The investigation of the geological structure of the underground structure area shall establish the major geotectonic position in which the area lies and the distribution and scale of the principal folds and fractures of the surrounding region.

4.1.4 item 2 The investigation of the folds of the underground structure area shall ascertain the attitude of the rock strata and the morphological features, the scale and the extent of the folds.

4.1.4 item 3 The investigation of the faults of the underground structure area shall ascertain the distribution and the attitude of the faults, the width of the fracture zone and of the zone of influence, and the composition of the structural rock group; the faults shall be grouped according to their attitude, graded according to their scale, and classified according to their nature. The grading of the structural planes of the rock mass in the underground structure area shall comply with the relevant provisions of the current national standard Code for Hydropower Engineering Geological Investigation, GB 50287.

4.1.4 item 4 Faults that have an important influence on the stability of the surrounding rock of the underground structures shall be the focus of the investigation. Where a tunnel crosses a possible active fault, the activity of that active fault and its influence on the tunnel works shall be studied. The study of fault activity shall comply with the relevant provisions of the current sector standard Specification for Regional Tectonic Stability Investigation of Hydropower Projects, NB/T 35098.

4.1.4 item 5 In the investigation of the joints and fissures of the underground structure area, it is advisable to survey and record statistically the number of joint and fissure sets, their preferred attitude, their spacing, their persistence, their roughness and waviness, the weathering and alteration of the fissure surfaces, their aperture, their infilling, the state of the groundwater and the volumetric joint count of the rock mass. The area of a statistical window should not be less than 10 square meters, the arrangement of the statistical windows shall be geologically representative, and their orientation shall be taken into account.

4.1.5 The investigation of the physical geological phenomena of the underground structure area shall meet the following requirements.

4.1.5 item 1 The investigation of the weathering characteristics of the rock mass of the underground structure area shall ascertain the degree and the depth of weathering, with emphasis on the distribution, the thickness and the properties of the several weathering zones in the entrance and exit sections of the caverns, in the shallow buried tunnel sections and in the layout section of the underground powerhouse. The subdivision of the weathering zones of the rock mass shall comply with the relevant provisions of the current national standard Code for Hydropower Engineering Geological Investigation, GB 50287.

4.1.5 item 2 The investigation of the stress relief characteristics of the rock mass of the underground structure area shall ascertain the degree and the depth of stress relief, with emphasis on the distribution, the thickness and the properties of the several relief zones in the portal sections, in the shallow buried tunnel sections and in the layout section of the underground powerhouse. The subdivision of the stress relief zones of the rock mass shall comply with the relevant provisions of the current national standard Code for Hydropower Engineering Geological Investigation, GB 50287.

4.1.5 item 3 The investigation of slope deformation and failure phenomena in the underground structure area shall ascertain the distribution, the scale and the developmental features of collapses, landslides and deformed rock bodies, with emphasis on the deformation and failure characteristics of the slopes in the portal sections, in the shallow buried tunnel sections and in the layout section of the underground powerhouse, and on the distribution and stability of the large collapses, landslides and deformed rock bodies along the tunnel alignment.

4.1.5 item 4 The investigation of debris flows in the underground structure area shall ascertain the distribution, the type, the scale, the characteristics of the catchment, the conditions of formation, the history of development and the trend of development of the debris flows, with emphasis on the developmental features of the debris flows in the vicinity of the cavern portals.

4.1.5 item 5 The investigation of abandoned mine workings and goaf areas in the underground structure area shall ascertain their distribution, their form, their scale, and the deformation and failure features at the ground surface and underground.

4.1.5 item 6 The investigation of freeze thaw weathering phenomena of the rock and soil masses of the underground structure area shall ascertain the distribution, the scale and the characteristics of the freeze thaw weathered layer and of the block debris, the freeze thaw rock debris flows and the freeze thaw mud flows formed from it, with emphasis on the freeze thaw weathering features of the rock and soil masses in the portal sections and in the shallow buried tunnel sections.

4.1.6 Karst investigation shall be carried out in the underground structure area. The karst investigation shall comply with the relevant provisions of the current sector standard Specification for Engineering Geological Investigation of Karst of Hydropower Projects, NB/T 10075.

4.1.7 The investigation of the hydrogeological conditions of the underground structure area shall meet the following requirements.

4.1.7 item 1 The investigation of the hydrogeological conditions of the underground structure area shall ascertain the basic type, the water level, the depth of burial, the water pressure, the water volume, the water temperature and the hydrochemical composition of the groundwater, as well as the water content and the permeability of the rock mass; it shall distinguish the aquifers from the relatively impermeable layers; and, in conjunction with the emergence of springs, it shall analyze the conditions of recharge, runoff and discharge of each aquifer and delimit the hydrogeological units.

The readable extract of the body text ends within article 4.1.7 at page 6 of the specification. The remaining provisions of subclause 4.1, the whole of subclause 4.2 on the investigation of engineering geological properties, and clauses 5, 6 and 7 continue in the printed volume as listed in the official Contents.