Detail of SL 253-2018

Introduction of SL 253-2018

Codeofchina.com is in charge of this English translation. In case of any doubt about the English translation, the Chinese original shall be considered authoritative. Design specification for spillway (SL 253-2000) is revised in accordance with the arrangement of development and revision plan of water conservancy technical standard and the requirements of SL 1-2014 Specification for the drafting of technical standards of water resources. The specification consists of 7 clauses and 2 annexes. ——Spillway layout. ——Hydraulic design. ——Structure design. ——Design of foundation and side slope treatment. ——Safety monitoring design. The main contents revised in this time are as follows: ——The “jet-flow atomization and anti-icing design” is added. ——The proposal of “main and auxiliary spillways" is deleted. ——The design contents of "ski jump spillway" and "free overflow tunnel spillway" are added. ——The types and design contents of step, narrow slit and energy dissipation by hydraulic jump with step-down floor are supplemented. ——The design flood standard for energy dissipation and scour prevention structures of spillway is not repeated and revised to be determined in accordance with the relevant provisions of SL 252 Standard for classification and flood control of water resources and hydroelectric project. ——The relevant provisions of spillway structural design are revised and the material physical and mechanical parameter table is canceled in accordance with the relevant provisions of SL 191-2008 Design code for hydraulic concrete structures. ——The Annex B “Anti-sliding stability and anti-shearing parameters of weir (sluice) foundation and weir body” in the former specification is canceled. ——The relationship is coordinated of the spillway load calculation, retaining wall design, side slope design and safety monitoring design to their corresponding special specifications, and Annex C “Load calculation formula”, Annex D “Side slope rock mass stability classification and treatment measures” and Annex E “Hydraulic monitoring design requirements” in the former specification are canceled. The mandatory provisions in this specification are items 1-4 in 3.3.9, item 3 in 5.3.9 and 5.3.13 and marked in bold and must be strictly implemented. The previous editions of this specification are as follows: ——SDJ 341-89; ——SL 253-2000. During the implementation of this standard, all organizations are kindly asked to pay attention to summing up experience, accumulating data and feeding relevant opinions and suggestions back to Ministry of Water Resources, Department of International Cooperation, Science Technology at any time (correspondence address: No.2, 2nd Lane, Baiguang Road, Xicheng District, Beijing; Postal code: 100053; Tel.: 0086-(0)10-63204533; E-mail: bzh@mwr.gov.cn) for reference in future revisions. Design specification for spillway 1 General provisions 1.0.1 This specification is formulated in order to regulate the spillway design and achieve safety and reliability, rational economy, advanced technology, environmental coordination and convenient management and operation. 1.0.2 This specification is applicable to the design of Classes 1, 2 and 3 spillways (including ski jump spillways and free overflow tunnel spillways) on rock foundations in large- and medium-sized water conservancy and hydropower projects. Reference may be made to this specification for the design of Classes 4 and 5 spillways. 1.0.3 Flood standard for spillway (including that for energy dissipation and scour prevention structures of spillway) shall be determined in accordance with the class of spillway and the provisions of SL 252 Standard for classification and flood control of water resources and hydroelectric project. 1.0.4 For spillways of large-sized projects or medium-sized projects with complicated hydraulic conditions, the rationality of project layout and hydraulic design shall be demonstrated based on hydraulic model tests. 1.0.5 For spillway design, the spillway operation and gate opening and closing mode shall be determined according to the flood control dispatching requirements of the project. 1.0.6 This standard mainly cites the following standards: GB/T 50662 Code for design of hydraulic structures against ice and freezing action GB 51247 Code for seismic design of hydraulic structures SL 74 Hydraulic and hydroelectric engineering specification for design of steel gate SL 191 Design code for hydraulic concrete structures SL 252 Standard for classification and flood control of water resources and hydroelectric project SL 265 Design specification for sluice SL 279 Specification for design of hydraulic tunnel SL 319 Design specification for concrete gravity dams SL 379 Design specification for hydraulic retaining wall SL 386 Design code for engineered slopes in water resources and hydropower projects SL 486 Technical specification for strong vibration safety monitoring of hydraulic structures SL 616 Specification for hydraulic prototype observation of water conservancy and hydropower projects SL 654 Specification for design of reasonable service life and durability of water conservancy and hydropower projects SL 725 Design specification for safety monitoring in water and hydropower projects SL 744 Design specification for load of hydraulic structures DL/T 5207 Technical specification for abrasion and cavitation resistance of concrete in hydraulic structures 1.0.7 In addition to this standard, the design of spillways shall also comply with those specified in the current relevant standards of the nation. 2 Terms 2.0.1 main spillway spillway that is used either alone or in combination with other outlet structures and whose discharge capacity meets the design flood standard requirements 2.0.2 emergency spillway spillway for discharging abnormal flood exceeding the design flood standard 2.0.3 free overflow spillway spillway with the inlet control section open and with the discharged water having free surface 2.0.4 normal channel spillway free overflow spillway with the chute axis orthogonal to the inlet overflow weir axis and with the flow through the weir in the same direction as the chute axis 2.0.5 side channel spillway free overflow spillway with the chute axis approximately parallel to the inlet overflow weir axis and with the flow through the weir approximately perpendicular to the chute axis direction 2.0.6 ski jump spillway free overflow spillway with the inlet control section at dam top, which discharges the water into river channel by making the water away from the dam toe with chute through flip shot 2.0.7 free overflow tunnel spillway spillway with all or part of the mountain body on the bank being tunnel, and with the discharged water having free surface within the whole course 2.0.8 control section weir or sluice (hereinafter referred to as weir) located between the intake canal and the chute to control the discharge of the spillway as well as the buildings connected on both sides 2.0.9 chute rapids discharge channel between the inlet control section and the outlet energy dissipation section of the spillway 2.0.10 flip bucket bucket built at the end of the outlet structure, capable of ejecting the discharged water downstream and having a certain reverse arc radius and a certain angle 2.0.11 energy dissipation by hydraulic jump energy dissipation mode dissipating the residual energy of the rapids discharged from the outlet structure by making use of hydraulic jump so that the rapids are changed into slow flow and join in the downstream water, also called as hydraulic jump energy dissipation 2.0.12 ski-jump energy dissipation energy dissipation mode ejecting the discharged rapids by the flip bucket built at the end of the outlet structure so that the rapids forms aerated jet flow and falls into the downstream water cushion 2.0.13 energy dissipation by hydraulic jump with step-down floor energy dissipation mode by hydraulic jump formed by setting step-down floor of certain height at the reverse arc section end and at the head of the stilling pool of the energy dissipation by hydraulic jump 2.0.14 continuous flip bucket continuous solid flip bucket built at the end of a outlet structure 2.0.15 slotted flip bucket flip bucket consisting of platforms and trenches in an alternate way or those with different cantilever angles set at different elevations 2.0.16 slit-type flip bucket flip bucket with the side wall of the chute at the outlet of the rapids forming slit due to sharp contraction 2.0.17 special-shaped convergent flip bucket special shape flip bucket formed by bottom surface twisting, angle-cutting at bucket end or other means 2.0.18 apron rigid bottom protection structure built at the downstream of the outlet structure to protect the riverbed from scour 2.0.19 cavitation water flow phenomenon of occurrence of cavity (involving the occurrence, development and perish of the cavity) when the absolute pressure of a certain place in high velocity flow is lower than the vaporization pressure of that place 2.0.20 cavitation damage (pitting) denudation deterioration of solid boundaries due to cavitation 2.0.21 jet-flow atomization physical phenomena of rain and fog caused by splashing and splitting of jet-flow energy dissipation nappe 3 Spillway layout 3.1 General requirements 3.1.1 Spillway may consist of buildings such as intake canal, control section, chute, energy dissipation and scour prevention facilities, and outlet canal. 3.1.2 Spillway layout shall be selected through technical and economic comparison based on factors such as topography, geology, hub layout, dam type, construction, ecology and environment, operation management and economic indicators. 3.1.3 For spillway layout, attention shall be paid to coordination of contradictions in the layout of buildings for flood discharge, power generation, shipping, floatage drainage, fish passage, ecology, water supply and irrigation, so as to avoid mutual interference and take into account the requirements of architectural landscape. 3.1.4 When suitable topographical and geological conditions are available, the spillway may be arranged as main spillway and emergency spillway according to the flood characteristics and its influence on the downstream through technical and economic comparison demonstration, and the spillway shall meet the following requirements: 1 Main spillway and emergency spillway should be arranged separately; centralized arrangement, if adopted, shall be fully demonstrated. 2 Emergency spillway should be of open type. Self-collapsing type or a blasting-induced collapse type, after being demonstrated, may also be adopted. 3 The downstream structure in the control section of emergency spillway may be simplified in combination with the topographical and geological conditions, but it shall not affect the safety of main buildings. 3.1.5 With main and emergency spillways arranged, the main spillway discharge capacity shall not be less than the discharge ought to be borne by the spillway under the design flood standard. The use standard of emergency spillway shall be determined according to the factors such as project grade, hub layout, dam type, flood characteristics and standards, reservoir capacity characteristics and influence on downstream. During flood discharge through emergency spillway, the maximum total discharge of the reservoir shall not exceed the natural peak discharge of the dam site with the same frequency. 3.1.6 Spillway discharge, total width of overflow front edge and elevation of weir crest or sluice bottom plate shall be selected through technical and economic comparison based on the following factors: 1 Reservoir characteristics and flood dispatching; 2 Coordination with other outlet structures in layout and application; 3 Topographical and geological conditions, and scour resistance of downstream riverbed and both banks; 4 River channel characteristics and energy dissipation requirements; 5 Connection with adjacent buildings; 6 Sluice type and sizing; 7 Operation and maintenance conditions; 8 Cost and maintenance charge. 3.1.7 Spillway shall be arranged on the bank or pass according to the topographical and geological conditions. It is appropriate to avoid high side slopes formed by excavation and to avoid gullies, collapse bodies and landslide bodies. 3.1.8 When the mountain on both sides of the dam site is steep and no pass is available, the side channel spillway, ski jump spillway or free overflow tunnel spillway may be adopted through technical and economic comparison. The layout shall meet the following requirements: 1 The layout of side channel spillway and that of dam abutment shall be coordinated; 2 The layout of the inlet section and control section of the ski jump spillway and that of the dam body and other buildings in the dam area; 3 The tunnel line layout of the tunnel section and cross section design of free overflow tunnel spillway shall meet the relevant provisions of SL 279. 3.1.9 Spillway shall be arranged on a stable foundation, taking into account the structural characteristics of the rock mass and geological structure, as well as the adverse effects of changes in hydrogeological conditions on the stability of buildings and side slopes after the construction of the reservoir. 3.1.10 When the spillway is close to the dam abutment, its layout and discharge shall not affect the stability of the dam abutment and bank slope. In the earth-rockfill dam hub, the joints, guide walls, chute side walls, etc. connected with the dam shall be safe and reliable. 3.1.11 Spillway layout shall make the water flow smooth and the axis should be straight. If it is necessary to turn for the axis, the bend should be set in the section of the intake or outlet canal. 3.1.12 For the spillway, layout of flood discharge energy dissipaters and the type of flood discharge energy dissipation shall be reasonably chosen. The outlet flow of it shall be smoothly connected with the downstream river channel to avoid serious scouring and siltation of the downstream riverbed and bank slopes of the dam site caused by the discharged water, which will affect the normal operation of other buildings in the hub. 3.1.13 The sluice hoisting equipment and basic pumping and drainage equipment of spillway shall be provided with standby power supply and powered reliably. 3.2 Intake canal 3.2.1 The layout of the intake canal shall follow the following principles: 1 Favorable topographical and geological conditions shall be selected. 2 The selection of the axis direction shall make the water inflow smooth, with good flow state; 3 When the channel is long and a transition section is set in front of the control section, the length of the transition section shall be determined according to conditions such as flow velocity, and shall not be less than 2 times the water depth in front of the weir; 4 When the canal turns, the turning radius of the axis should not be less than 4 times the width of the canal bottom, and there shall be a straight section with length not less than 2 times the water head on the weir between the bend and the weir. 3.2.2 The inlet layout of the intake canal shall be adjusted to local conditions to make the water flow smoothly into the canal. The inlet shape shall be simple and meet the following requirements: 1 When the inlet is arranged at the dam abutment, a curved guide wall in the water flow direction shall be arranged on the side close to the dam, and the side close to the mountain shall be excavated or lined into a regular curved surface; 2 When the inlet is arranged at the pass, it should be arranged in a symmetrical or basically symmetrical bell mouth type. 3.2.3 The bottom width of the intake canal may be of equal width or reduce along the direction of water flow. The ratio of the bottom widths of the head and end of the intake canal should be 1~3. The joint with the control section shall be of equal width with the overflow front edge. The bottom plate should be flat or reverse slope slightly inclining towards upstream. 3.2.4 The bottom of the intake canal may not be lined; when the head loss is large, the canal bottom lining shall be determined through economic comparison. When the requirements of non-flushing flow rate are not met, lining shall be applied. 3.2.5 The type of the leading wall in the control section of the intake canal shall make the flow state good. The length of the leading wall along the water flow direction should be greater than 2 times the water depth in front of the weir, and the wall top shall be higher than the highest reservoir water level during flood discharge. 3.2.6 The intake canal guide wall close to the earth-rockfill dam body shall meet the following requirements: 1 The lower limit of the length of the guide wall in water flow direction shall be such that the slope toe of the adjacent dam is blocked; 2 The top of the guide wall within the range 2 times the depth of water in front of the weir in the control section shall be higher than the highest reservoir water level during flood discharge. 3 The guide wall beyond the range 2 times the depth of water in front of the dam may be set as submerged type, with the top of the wall higher than the dam surface by an appropriate height. 4 The guide wall layout and structural design shall meet the requirements of seepage prevention and stability, and shall be coordinated with dam seepage prevention system and deformation. 3.3 Control section 3.3.1 The control section shall include weirs and buildings connected on both sides. 3.3.2 The weir layout shall meet the following requirements: 1 Overall consideration shall be given to the general layout requirements of intake canal, chute, energy dissipation and scour prevention facilities and outlet canal; 2 Requirements of buildings on bearing capacity, stability, seepage resistance and durability of foundation; 3 It shall facilitate external traffic and the layout of buildings on both sides; 4 When the weir is close to the dam abutment, it shall be coordinated with the dam layout. 5 It shall be convenient to arrange the anti-seepage system so that the weir and the systems for water stop, anti-seepage and drainage on both banks or of the dam form a whole. 3.3.3 The weir type shall be selected through comparison according to the topographical and geological conditions, hydraulic conditions, application requirements and technical and economic indicators, and open overflow weir should be selected. Weir types of practical weirs, broad crested weirs, hump weirs that are open or with breast wall orifice may be adopted. 3.3.4 The weir crest elevation, overflow front edge length, weir crest sluice setting, sluice type, sluice size and quantity, sluice pier type and size, etc. shall be determined through technical and economic comparison, taking into account factors such as engineering safety, flood dispatching, operating conditions, inundation loss, engineering investment, etc. 3.3.5 The setting of overhaul sluice shall be determined according to the engineering safety and operation needs. When the overflow weir crest is under water all the year round, an overhaul sluice shall be set. 3.3.6 The side weir of the side channel spillway may be practical weir. Narrow and deep trapezoidal cross-section should be adopted as the side channel cross-section. The slope ratio of the side slope close to the mountain may be determined according to the geological conditions. The side slope close to the weir should not be steeper than 1:0.5. 3.3.7 The type and size of sluice piers shall meet the requirements for layout of sluice, traffic bridge and working bridge, water flow conditions, structure, operation and maintenance, etc. 3.3.8 The layout of the working bridge and traffic bridge on the weir shall be determined according to the requirements of project operation, observation, overhaul, traffic and sluice hoisting equipment layout. The clearance under the bridge shall meet the requirements of flood discharge and floatage drainage. When flood control and emergency rescue are required, traffic bridge and working bridge shall be set up separately. 3.3.9 The elevation of the sluice pier and the top of bank wall at the control section shall meet the following requirements: 1 When discharging the check flood, it shall not be lower than the check flood level plus heightening value for safety. 2 When retaining water, it shall not be lower than the design flood level or the normal water storage level plus the calculated wave height and heightening value for safety. 3 When the spillway abuts against the dam abutment, the top elevation of the control section shall be coordinated with that of the dam crest. 4 The lower limit heightening value for safety shall be selected according to Table 3.3.9.

Contents of SL 253-2018

Foreword ii 1 General provisions 2 Terms 3 Spillway layout 3.1 General requirements 3.2 Intake canal 3.3 Control section 3.4 Chute 3.5 Energy dissipation and scour prevention facilities 3.6 Outlet canal 4 Hydraulic design 4.1 General requirements 4.2 Intake canal 4.3 Control section 4.4 Chute 4.5 Energy dissipation and scour prevention 4.6 Outlet canal 4.7 Anti-cavitation damage design 4.8 Jet-flow atomization and anti-icing design 5 Structural design 5.1 General requirement 5.2 Intake canal lining 5.3 Control section 5.4 Chute bottom slab 5.5 Flip bucket 5.6 Stilling pool base slab 5.7 Side walls 5.8 Downstream protection 6 Design of foundation and side slope treatment 6.1 General requirement 6.2 Foundation excavation 6.3 Consolidation grouting 6.4 Seepage prevention and drainage of the foundation 6.5 Fault, weak interlayer and karst treatment 6.6 Side slope excavation and treatment 7 Safety monitoring design 7.1 General requirement 7.2 Monitoring items Annex A Calculation equations for hydraulic design A.1 Weir surface curve A.2 Equation for calculating discharge capacity A.3 Hydraulic calculation of chute A.4 Ski-jump energy dissipation A.5 Slit-type ski-jump energy dissipation A.6 Energy dissipation by hydraulic jump A.7 Design to prevent cavitation damage of water flow A.8 Table of roughness values commonly used in hydraulic calculation Annex B Calculation of anti-floating stability of stilling pool bottom slab B.1 Load combinations and calculation equations B.2 Load calculation Explanation of wording in this specification