SL 189-1996 Design Guidelines for Rolled Earth-Rock Dams of Small-Scale Water Conservancy and Hydropower Projects SL 189-96
Some standard content:
Industry Standard of the People's Republic of China
Small Size Water Resources and Hydroelectric Engineering
Design Guide for Rolled Earth Rock Fill Dams in Small Size Water Resources and Hydroelectric Engineering
SL 189—96
Design Guide for Rolled Earth Rock Fill Dams in Small Size Water Resources and Hydroelectric Engineering
SL 189—96
Editing unit:
Approving department:
1997—02—13Issued
Tianjin Water Resources and Hydropower Survey and Design Institute, Ministry of Water Resources, Ministry of Water Resources of the People's Republic of China
1997—05—01Implemented
Ministry of Water Resources of the People's Republic of China
Ministry of Water Resources of the People's Republic of China
Notice on the approval of the release of the "Design Guidelines for Roller-Compacted Earth-Rock Dams in Small Water Conservancy and Hydropower Projects"
SL189-96
Water Science and Technology [1997] No. 48
In accordance with the Ministry's plan for the formulation and revision of technical standards for water conservancy and hydropower, the "Design Guidelines for Roller-Compacted Earth-Rock Dams in Small Water Conservancy and Hydropower Projects" hosted by the China Water Resources and Hydropower Planning and Design Institute and edited by Tianjin Water Resources and Hydropower Survey and Design Institute has been reviewed and approved as a water conservancy industry standard and is now released. The name and number of the standard are: "Guidelines for the Design of Roller Compacted Earth-Rock Dams for Small Water Conservancy and Hydropower Projects" SL189-96. This standard shall be implemented from May 1, 1997. All units are advised to pay attention to combining with reality and summarizing experience. If there are any questions, please inform the General Institute of Water Conservancy and Hydropower Planning and Design, which will be responsible for interpretation.
The standard text is published and distributed by China Water Conservancy and Hydropower Press. February 13, 1997
Subject
1 General
2 Dam site selection and hub layout
2.1 Dam site selection
2.2 Hub layout
3 Dam type selection
4 Dam construction materials and filling standards
4.1 Dam construction materials
4.2 Filling standards
5 Dam foundation treatment
Sand and gravel foundation treatment
Liquefied soil and soft soil foundation treatment
Collapse loess foundation treatment
Rock and karst foundation treatment
Dam body and Connection between foundation and bank slope
6 Dam structure
Dam crest superelevation
Dam crest structurewwW.bzxz.Net
6.4 Impermeable body
Filter layer and transition layer
Dam body drainage
Dam surface drainage
7 Dam calculation
7.1 Seepage calculation
7.2 Stability calculation
7.3 Settlement calculation
8 Observation design
Additional instructions
1 General provisions
1.0.1 These guidelines are formulated to standardize the design of rolled earth-rock dams for small-scale water conservancy and hydropower projects. 1.0.2 This guideline applies to the design of grade 4 and 5 rolled earth-rock dams with a dam height of less than 30m in the "Classification and Design Standards for Water Conservancy and Hydropower Projects" (mountainous and hilly areas) (SDJ12-78) and grade 4 and 5 rolled earth-rock dams in the "Classification and Design Standards for Water Conservancy and Hydropower Projects" (plain and coastal areas) (SDJ217-87).
1.0.3 The design of small earth-rock dams should be based on respect for science, fully absorb the experience of existing projects, strive to improve the design level, and make the design conform to objective reality.
1.0.4 The dam site, reservoir area and material yard should be surveyed, geologically investigated and explored. For simple rock foundations, geological personnel can conduct surveys and submit geological reports. For complex rock foundations and overburden, the engineering geological conditions of the dam site should be identified. 1.0.5 Hydrological and meteorological surveys should be conducted for small earth-rock dam hub projects, and hydrological analysis and water conservancy calculations should be done. If the river where the project is located lacks measured data, the local "Hydrological Atlas" and "Hydrological Manual" can be used to calculate the annual runoff and annual distribution of different frequencies, the amount of rainstorms of different durations, the peak flow, the flood volume and the flood process line. If conditions permit, the historical floods in the reservoir and dam area should also be investigated. 1.0.6 In addition to complying with this guideline, the design of the rolled earth-rock dam of small water conservancy and hydropower projects should also comply with the relevant provisions of the current national and industry standards.
2 Dam site selection and hub layout
2.1 Dam site selection
The dam site selection should comprehensively consider the topography, geology, building materials, hub layout and upstream and downstream conditions, and be determined after comparing the plans. 2.1.1
2.1.2 It is advisable to build the dam on a rock foundation with simple geological structure, a gravel foundation with a small thickness or a dense soil foundation. The dam site should not be selected in a deep and highly permeable gravel layer, a karst development area, a severely weathered and broken rock layer, a large fault zone, or a weak foundation. If it cannot be avoided, treatment measures should be taken. 2.1.4 When selecting a dam site, it should be considered that after the reservoir is filled with water, no large bank or landslide will occur in the reservoir area. In hilly and plain areas, too large an immersion area should be avoided.
2.1.5 The basic earthquake intensity of the dam site area should be determined according to the China Earthquake Intensity Zoning Map (1990). The basic intensity can be used for the fortification intensity. In areas where the basic earthquake intensity is 6 degrees or above, buildings should take earthquake-resistant measures in accordance with the relevant provisions of the "Code for Seismic Design of Hydraulic Structures" (SDJ10-78).
2.2 Hub layout
2.2.1 The earth-rock dam hub is generally composed of a dam, a spillway, a water tunnel and a power station, and whether to set up a spillway tunnel is determined according to needs. The hub layout should be compact, meet functional requirements, save engineering work, and facilitate construction and operation management. 2.2.2 The dam axis and dam type should be selected according to the topographic and geological conditions and the overall layout of the hub; the dam crest elevation, cross-sectional dimensions and foundation treatment measures should be determined.
The dam axis should be a straight line. If a turn is required, it should be arranged in a curve at the turn. The dam shoulders on both sides should choose a gentle slope. 2.2.3 The spillway should be built on a natural mouth. For example, the Wu Tianran Pass, the spillway can be arranged near the dam head, the dam slope near the spillway inlet should be reliably protected, and the spillway outlet should take good energy dissipation measures, and the water flow after energy dissipation should not wash the dam foot. 2.2.4 The spillway should be arranged in a straight line. If a bend is set, it should be set on the inlet and outlet sections. The radius of curvature should not be less than 4 times the width of the channel bottom.
2.2.5 The spillway should preferably adopt the open-knock type, and it should not be equipped with gates. The elevation of the weir top should be flush with the normal water storage level. If there are flood control requirements downstream or the water storage level needs to be raised after the flood, the spillway can also be equipped with gates, but reliable safety measures must be taken. 2.2.6 The spillway should be selected on a rock foundation, and the length of the building's masonry protection depends on the terrain, geological conditions and anti-scouring requirements. Soft foundation spillways should be built on dense soil layers, and the protection and energy dissipation facilities of the inlet and chute should be well prepared, as well as the anti-seepage and drainage of the building. 2.2.7 The spillway or water diversion tunnel can be a tunnel or a dam-underground pipe management, but a tunnel should be preferred, which should be determined based on the terrain, geology, construction, cost and operating conditions.
2.2.8 The buried pipe under the dam should be built on a rock foundation. If it is necessary to install it on a soft foundation, the foundation treatment must be done well. In areas with an earthquake intensity of 7 degrees or above, buried pipes under the dam should not be installed on soft foundations.
2.2.9 The axis of the buried pipe under the dam should be consistent with the mainstream direction of the river. The pipe body should be arranged in a straight line. 2.2.10 The buried pipe under the dam should adopt open flow. In addition to determining the size of the pipe body according to the needs of hydraulic calculation, the requirements for inspection and maintenance should also be considered. 2.2.11 When the buried pipe under the dam is an open flow, concrete or reinforced concrete structure should be used, and mortar masonry should not be used. If it is a pressure flow, steel pipes or reinforced concrete pipes should be used. Cylinder tile pipes are strictly prohibited for buried pipes under the dam
3 Dam type selection
Small rolled main rock dams can adopt homogeneous earth dams, earth-rock dams with earth-based impermeable bodies, earth-rock dams with artificial impermeable bodies, and water-passing earth-rock dams.
(1) The dam body of a homogeneous earth dam is composed of soil materials with similar properties, and the dam body should meet the anti-seepage requirements. (2) The earth anti-seepage body of a core wall earth-rock dam is located in the middle of the dam body, and the rest of the dam body is filled with permeable materials (sand, gravel or rockfill). The earth anti-seepage body of a sloping core wall dam is slightly inclined upstream. The earth anti-seepage body of a sloping wall earth-rock dam is located upstream of the dam body, and the rest of the dam body is filled with permeable materials (sand, gravel or rockfill). A thicker gravel layer or rockfill layer can also be set upstream of the earth sloping wall. (3) The anti-seepage body of an artificial anti-seepage earth-rock dam can be made of reinforced concrete, asphalt concrete, geomembrane and other materials, and the rest of the dam body is filled with gravel or rockfill. The anti-seepage body can be located upstream, in the middle or slightly upstream of the middle. (4) Water-passing earth-rock dams can be divided into water-passing rockfill dams and water-passing earth dams according to the main materials of the dam body. 3.0.2 The selection of dam type should comprehensively consider the following factors and be selected after technical and economic comparison: the topography and geological conditions of the dam site: including the river valley topography, the rock properties of the dam foundation, the thickness, stratification and properties of the overburden, earthquake intensity, etc.; the physical and mechanical properties, reserves, location, and mining, transportation and filling conditions of the dam-building materials (including the hub building and the slag excavated); the overall layout of the project and the connection between the dam body and the flood discharge and water conveyance structures; (4) Dam foundation treatment method: Construction conditions include the meteorological and hydrological conditions of the dam site during the construction period, site layout conditions, construction technology level and experience, etc.; engineering volume and investment. When there is soil material of suitable nature and sufficient quantity near the dam site, a homogeneous dam should be selected. 3.0.4 Concrete face rockfill dam should be built on a rock foundation. If there is no soft soil layer such as silt and fine sand in the gravel of the dam foundation, the dam body can also be placed on a gravel foundation.
3.0.5 The toe plate of the concrete face dam should be placed on the rock foundation. If the toe plate is built on the gravel foundation, it should be well treated for anti-seepage. 3.0.6 Small rolled earth-rock dams can use geomembranes as anti-seepage materials. 3.0.7 Rigid core dams should not be built in earthquake zones with magnitudes of 7 or above. 3.0.8 When the dam site does not have suitable topographic and geological conditions for arranging a bank spillway, a water-passing earth-rock dam can be used after technical and economic comparison. The values of dam height and single width flow can be selected according to Table 3.0.8. Table 3.0.8 Maximum dam height and single-width flow rate of earth-rock dams Reinforced concrete King
Maximum dam height (m)
Asphalt concrete
Mortared stone, King
Stone-strip facing
Note: When the values in the table are exceeded, special demonstration should be made. 3.0.9 The construction of earth-rock dams should meet the following requirements: Single-width flow rate [m3/(s·m)]]
Reinforced concrete
Asphalt concrete
Mortared stone, King
Stone-strip facing
(1) Earth-rock dams should adopt inclined wall dam type. The downstream dam body should be filled with gravel or rockfill and compacted. The overflow panel should be constructed after the dam body section is filled.
(2) The overflow panel should be well designed. For higher dams, concrete or reinforced concrete impermeable panels should be used, and the upstream can be provided with tooth grooves embedded in the dam body.
The surface of the panel should be flat, and the connection should prevent the downstream block from being higher than the upstream block. Water stops should be set at the joints, and a filter drainage cushion layer should be laid under the surface. (3) The earth-rock dam should be built on a rock foundation. If it is built on a gravel cover layer, energy dissipation facilities should be well prepared. (4) When asphalt concrete is used as the surface protection of the earth-rock dam, attention should be paid to preventing freezing cracks in cold areas; attention should be paid to preventing asphalt flow in hot areas.
4 Dam construction materials and filling standards
4.1 Dam construction materials
Investigation and geotechnical tests should be conducted on dam construction materials to find out the properties, reserves, mining conditions and transportation distances of various natural earth and stone materials. 4.1.1
4.1.2 The following principles should be followed in selecting earth and rock materials for dam construction: (1) The earth and rock materials for filling the dam body should have physical and mechanical properties suitable for their purpose of use and have good long-term stability; (2)
Under the premise of not affecting the safety of the project, materials near the dam site and excavated materials of the hub building should be used first, and less or no farmland should be occupied;
It is convenient for mining and transportation.
Soil materials with a water-soluble salt content greater than 5%, soil materials with an organic matter content greater than 5%, dry and hard clay, dispersed soil, soft clay, etc. are not suitable for dam construction.
The impermeable body can be filled with clay soil and gravel soil (including weathered rock materials). The permeability coefficient after compaction is not greater than 1×104.1.4
4cm/s for homogeneous earth dams; and not greater than 1×10-5cm/s for core walls, inclined walls and blankets. The anti-seepage body should be filled with soil with a plasticity index of Ip=7~20. If soil with a lower plasticity index is used, the thickness of the anti-seepage body should be appropriately increased and the filter layer should be well prepared.
The water content of the soil should be close to the optimum water content. If there is a large difference, it should be treated. 4.1.5 The content of gravel soil (including rock weathering material) used for the anti-seepage body with a particle size greater than 5mm should not be greater than 50%, and the content of particle size less than 0.074mm should not be less than 15%. The maximum particle size should not exceed 15cm or 2/3 of the soil thickness, and coarse particle concentration should not occur. 4.1.6 If there is a lack of natural anti-seepage soil materials in the local area, clay soil, sandy soil and gravel, or a mixture of clay soil and gravel can be used as anti-seepage materials, but they should be mixed evenly and meet the requirements of Articles 4.1.4 and 4.1.5. 4.1.7 When gravel soil (including weathered rock material) or admixture is used as the anti-seepage material of the dam, the gradation range of the soil material should be proposed through tests. 4.1.8 Slope residual red soil or red soil-like soil with stable granular structure has high water content and low dry density, but high shear strength, low permeability and low compressibility, and can be used to fill the anti-seepage body of the earth-rock dam. 4.1.9 When using expansive soil to fill the anti-seepage body, a sufficient weight protection layer should be set. 4.1.10 When using collapsible loess to build a dam, its original structure should be destroyed, and the filling water content should be equal to or slightly greater than the optimal water content. 4.1.11 Frozen soil should not be used to build a dam. When using frozen soil to build a dam, the content of frozen soil blocks shall not be greater than 10%; the maximum diameter of frozen soil blocks shall not be greater than 1/2 of the thickness of the soil, and the water content of frozen soil shall be equal to or slightly lower than the plastic limit water content. 4.1.12 The dam shell shall meet the requirements of dam body stability and drainage. Medium-coarse sand, gravel, slag or rockfill should be used for filling. Uniform medium-fine sand and silt can be used in the dry area of the dam shell. For soft rock weathered stone materials with low strength, the gradation change after compaction and the reduction of strength and permeability after immersion in water should be considered, and they should be used in appropriate parts of the dam shell.
4.1.13 Rockfill or gravel materials should be used for the dam body of concrete face dam and asphalt concrete face dam. After compaction, it should have low compressibility, high shear strength and free drainage capacity. The mud content (particle size d<0.1mm) should not exceed 5%. 4.1.14 Stone materials with high compressive strength and weathering resistance should be used for upstream slope protection and drainage facilities. The ratio of the maximum side length to the minimum side length of the block stone should not be greater than 2.0, and the block diameter and weight of the stone should meet the requirements of wind and wave resistance. 4.1.15 The filter layer, cushion layer and transition layer of the dam should use medium-coarse sand, natural gravel or screened material, or rock rolled material. The particle gradation should meet the requirements of filter drainage and have long-term stability. The mud content (d<0.1mm) should be less than 5%. 4.1.16 In areas where natural anti-seepage materials are lacking, artificial materials such as concrete, asphalt concrete or geomembrane can be used as anti-seepage bodies. 4.1.17 The face plate and toe plate of the concrete face rockfill dam should meet the requirements of anti-seepage, durability and frost resistance. The concrete should be graded in two levels, and its grade should not be lower than C20. Ordinary Portland cement should be used. The face plate can be 30cm thick plate. 4.1.18 The asphalt concrete anti-seepage body should meet the requirements of anti-seepage, crack resistance, stability and durability. The coarse aggregate should be crushed stone rolled from alkaline rocks (limestone, dolomite, etc.). The fine aggregate can be natural coarse sand or artificial rolled sand. The aggregate should be hard and fresh. The mud content of coarse aggregate should not be greater than 0.5%, and the mud content of fine aggregate should not be greater than 2%. Fillers can be limestone powder, dolomite powder or talcum powder. Admixtures should be selected through tests based on requirements such as improving the properties of asphalt mixtures and improving the physical and mechanical indicators of asphalt concrete. 4.1.19 The geomembrane used for anti-seepage and the geotextile used for filtration and drainage in earth-rock dams should meet the physical and mechanical properties, hydraulic properties and durability that are compatible with engineering requirements.
When using geotextiles as filtration materials, the particle gradation between them and the protected soil should meet the filtration and drainage criteria. They can be selected based on seepage conditions, soil properties, load conditions, etc.
Geomembrane or geotextile can be selected based on the experience of existing projects. 4.2 Filling standards
4.2.1 The dam body should be dense and uniform, have sufficient shear strength, low compressibility, and meet the requirements of seepage control. Reasonable filling standards should be specified so that the compaction of fill meets both safety requirements and economic rationality. During the construction process, the prescribed filling standards should be checked and revised. 4.2.2 For cohesive soil materials, the compacted dry density shall be determined by multiplying the maximum dry density of the standard compaction instrument test by the compaction degree. The compaction degree can be taken as 0.950.97.
The moisture content of the fill soil shall be controlled according to the optimal moisture content, with an allowable deviation of 3%. If there is no test data, it can be determined based on the properties of the soil material and the experience of similar local built projects. 4.2.3 For gravel soil, a large compaction instrument should be used to conduct a full-sample compaction test to obtain the maximum dry density and optimal moisture content of the full sample with different coarse material (d≥5mm) contents, and then multiply the maximum dry density by the compaction degree of 0.95~0.97, as the dry density of gravel soil filling. When there is no condition to conduct large-scale compaction test, it can be determined according to the following two situations based on the different coarse material content: (1) For gravel soil with coarse material content less than 40%, the fine material (d < 5mm) can be taken for compaction test to determine the maximum dry density and optimal water content of the fine material. The maximum dry density and optimal water content of the gravel soil sample corresponding to different coarse material contents can be calculated using formula (4.2.3-1) and formula (4.2.3-2), and multiplied by the compaction degree to obtain the gravel soil filling standard. 1
(pa)+-
Z（a)o
op=00(1P)
wherein (>d)max—maximum dry density of gravel soil; P—gravel content with particle size d>5mm, in decimal; A—specific gravity of gravel with particle size d>5mm;
(4.2.3—1)
(4.2.3—2)
(>d)o——maximum dry density of fine-grained soil with particle size d>5mm; op——optimal moisture content of gravel soil:
0o——optimal moisture content of fine-grained soil with particle size d<5mm. (2) For gravel soil with coarse material content greater than 40%, the calculated maximum dry density and optimal moisture content of the whole sample should also be corrected, or the compaction degree should be appropriately reduced. The filling standard is determined accordingly. 4.2.4 The compaction standard of sand and gravel should be controlled by relative density (D), requiring D.≥0.7. When there is a lack of test data, dry density (yd) can also be used for control, requiring sand d=1.6~1.7g/cm2; when the gravel content of gravel is 40%~70%, take 2.0g/cm3 according to different gravel contents.
The compaction standard of rockfill should be controlled by porosity (n), requiring n=20%~30%. The compaction standard for the dam body of concrete face dam and water-passing earth-rock dam should take the larger value. 5 Dam foundation treatment
5.1 Gravel foundation treatment
5.1.1 Before selecting foundation treatment measures, the plane distribution and spatial distribution of the gravel layer of the dam foundation, the grading of gravel, water permeability, seepage stability, the presence of weak interlayers, the presence of concentrated seepage zones, and the condition of the bedrock should be found out. In the terraced area, it should be found out whether there are double layers of clay on the surface and gravel below, or multiple layers of clay and gravel interlayered.
5.1.2 When using dam foundation anti-seepage and downstream drainage facilities for gravel dam foundation seepage control, it should be determined after comprehensive analysis and comparison based on the dam type, the nature of the dam foundation cover layer, the allowable seepage volume, construction conditions and engineering costs. Dam foundation anti-seepage can be achieved by using intercepting ditches, blankets, or using high-pressure jet grouting technology to build anti-seepage walls. After technical and economic comparison, concrete anti-seepage walls and other measures can also be used. Downstream drainage facilities can be horizontal drainage mattresses, prism drainage, dam toe drainage ditches, pressure relief wells and permeable cover weights. 5.1.3 When the thickness of the gravel cover layer is less than 15m, intercepting ditches should be used. 5.1.4 The intercepting ditches should be arranged below the anti-seepage body. The intercepting ditches of homogeneous earth dams can be arranged within the range of the lower 1/3 of the dam bottom width from the dam axis to the upstream dam foot. 5.1.5 The bottom width of the intercepting ditch shall be determined according to the permissible seepage gradient of the backfill soil. Permissible seepage gradient: 2-4 for light loam, 3-5 for loam, and 5-7 for clay. The minimum bottom width shall not be less than 3.0m. The excavation slope of the intercepting ditch is determined by the shear strength of the cover material and the excavation depth, and can be 1:15~1:2.
The intercepting ditch should be filled with the same soil as the dam body impermeable body, and its compacted dry density should be the same as the dam body impermeable body. When the interlayer coefficient between the soil of the intercepting ditch and the gravel of the dam foundation exceeds the specified value, an anti-filtration layer shall be set on the downstream surface of the intercepting ditch. 5.1.6 The depth of the intercepting ditch embedded in the relatively impermeable layer, impermeable layer or weakly weathered rock (including the riverbed and both banks) shall not be less than 0.5m. If cracks are developed on the surface of the bedrock, they can be filled with cement mortar, or a layer of concrete can be laid to separate the cracks from the dam body fill. If necessary, the bedrock can be grouted.
5.1.7 If the dam foundation is a stratum with alternating gravel layers and weak permeable layers, and the permeability coefficients of the weak permeable layers and gravel layers differ by more than 100 times, and they are of a certain thickness and continuous, the upper gravel layer can be dug through and the intercepting channel can be built on the weak permeable layer. 5.1.8 If the gravel cover layer of the dam foundation is relatively thick, it is difficult to dig the intercepting channel and vertical anti-seepage measures are required, high-pressure jet grouting or concrete anti-seepage walls can be adopted.
5.1.9 When the gravel cover layer is relatively thick, upstream blanketing can be used for anti-seepage and downstream backfiltration and drainage can be used. When the gravel cover layer is thick and the permeability coefficient is large, it should be studied whether the blanketing can achieve the expected anti-seepage effect. 5.1.10 The blanketing design should determine the reasonable length, thickness and permeability coefficient of the blanketing so that the seepage gradient and seepage volume of the dam foundation are controlled within the allowable range.
The length of blanket should not be less than 5 times the water head. The thickness of the upstream end of blanket should be 0.51.0m, and the thickness of the end connecting with the anti-seepage body should meet the requirements of dam foundation seepage and blanket allowable slope, but should not be less than 2.5m. Blanket should be filled with clay with a permeability coefficient equal to or less than 10-cm/s. 5.1.11 Silt and humus on the blanket foundation surface should be completely removed. Pit sampling should be carried out in the blanket foundation to understand its particle composition. The foundation surface should be compacted and leveled, and there should be no gravel concentration. The anti-filtration principle should be met between the main material of blanket and the gravel of dam foundation, otherwise an anti-filtration layer should be set. 5.1.12 When using natural soil layer as blanket, its distribution, thickness and permeability should be understood to determine its anti-seepage effect and whether it is necessary to add artificial blanket or other reinforcement measures.
When taking soil to build a dam upstream of the dam, it must be limited to taking soil outside a certain range of the upstream dam foot. 5.1.13 When using geomembrane as blanket for anti-seepage, the laying, bonding and protection of the geomembrane should be done well to avoid damage. 5.1.14 After the blanket is completed, loose soil or slag should be laid on the surface for protection. In areas that may be eroded by waves, stone (slag) materials should be laid on the blanket for protection.
5.1.15 After adopting vertical anti-seepage measures, the seepage of the dam foundation can be controlled, and the downstream drainage measures can be appropriately simplified. Inverted filtration drainage ditches can be set at the toe of the dam.
When using blanket for anti-seepage, drainage facilities such as horizontal drainage mattresses, rockfill prisms, and inverted filtration drainage ditches should be set downstream. If necessary, pressure relief wells and downstream permeable cover weights should be set.
5.1.16 The bottoms of all drainage bodies should be set on permeable foundations. If the surface layer of the dam foundation is a thin aquitard, the aquitard should be dug through; if the aquitard is very thick, a pressure relief well extending into the aquitard can be used to lead the seepage water to the downstream dam foot drainage ditch. The depth of the pressure relief well and the depth of the aquitard should not be less than 1/2 of the thickness of the aquitard. The drainage ditch should have sufficient drainage section and good anti-filtration design. A transverse (vertical to the dam axis) drainage ditch should be set up to lead the seepage water to the downstream. 5.1.17 Anti-filtration drainage should be laid in the foundation range where the outflow slope of the downstream dam is greater than the allowable value. If necessary, a permeable cover layer should also be laid, and the permeable cover layer and the foundation should meet the principle of anti-filtration requirements. 5.2 Treatment of liquefiable soil and soft soil foundation
5.2.1 The possibility of earthquake liquefaction should be considered for saturated silt, fine and medium sand foundations and less cohesive soil foundations (such as saturated sandy loam, silty sandy loam, light loam, light silty loam, etc.) located in earthquake zones. The liquefaction evaluation method shall be carried out in accordance with Appendix 1 of the Code for Seismic Design of Hydraulic Structures. 5.2.2 For soil layers that are judged to be likely to liquefy, it is advisable to excavate and replace them with soil materials that meet the requirements. If excavation is difficult or uneconomical, reinforcement measures should be taken to achieve a compacted state that is compatible with the design earthquake intensity. The reinforcement measures that can be used are:
(1) Surface compaction method;
Surface vibration compaction method;
Deep explosion method;
Sand pile compaction method;
Vibroflotation reinforcement method;
Strong compaction method.
Soft soil has low bearing capacity, high compressibility and low shear strength. If a dam is to be built on it, foundation treatment must be carried out. The treatment methods can be:
Sand replacement method;
Suppression platform method;
Sand well plus horizontal drainage mattress method;
Vibro-impact reinforcement method;
(5) Geosynthetics padding method.
The above methods can be used in one or a combination, which should be determined after technical and economic comparison. 5.2.4 When any method is used to treat soft soil foundation, the dam filling rate should be controlled. In order to determine the safe filling rate, dam foundation displacement settlement points should be set at the upstream and downstream dam feet. If necessary, pore water pressure observation facilities can be set. 5.3 Treatment of collapsible loess foundation
5.3.1 Collapsible loess foundation should be treated. 5.3.2 For the collapsible loess foundation with small thickness, the collapsible property can be eliminated by excavation, overturning or surface compaction. On the premise of ensuring the stability of the dam body, the soil layer with low surface dry density and high collapsibility can also be excavated, and the lower part of the soil layer can be retained. 5.3.3 When the collapsible loess of the dam foundation is thick, it is advisable to use the pre-immersion method. When the thickness of the collapsible loess layer exceeds 15m, drilling or vertical deep pre-immersion can be used to accelerate the immersion process. The scope of the pre-immersion treatment should be larger than the scope of the dam foundation, and the pre-immersion boundary should be twice the immersion depth in the upstream and downstream directions of the dam foundation. The dam foundation immersion treatment should be combined with the dam body filling to increase the pressure and accelerate the collapse. 5.3.4 When the dam foundation is collapsible loess, it can also be treated by the strong tamping method. The number of tamping times and the depth of influence are determined by experiments. 5.3.5 When the collapsible loess foundation is treated by the vibroflotation method, the hole spacing, hole diameter and hole depth should be determined by referring to the experience of existing projects or experiments. 5.3.6 Underground cavities such as sinkholes, animal nests, caves, and tombs in the loess of the dam foundation must be identified and treated. 5.4 Treatment of rock and karst foundations
5.4.1 When the permeability of the rock foundation is high and affects the water storage of the reservoir and the safety of the dam body and dam foundation, treatment measures should be taken. 5.4.2 When there are joint and fissure intensive zones or fault fracture zones in the rock foundation within the range of the dam foundation or the intercepting channel, the corresponding treatment measures should be determined according to their occurrence, width, depth, and the impact of piping and dissolution on the dam foundation and dam body. Possible treatment measures:
(1) Excavate the tooth groove and backfill with concrete:
(2) Expand the bottom width of the intercepting channel;
(3) Lay the filter layer at the exposed part of the downstream fault and fracture zone. Grouting treatment should be carried out when necessary. 5.4.3 When building a dam in a karst area, the entire topographic, geological and hydrogeological conditions of the reservoir and dam area and the distribution of karst should be investigated. 5.4.4 Treatment of karst foundations can be carried out by interception, blocking, enclosure, paving, isolation and other methods. Depending on the project and leakage conditions, one type or a combination of several types can be used.
5.4.5 The foundation treatment of concrete face rockfill dams built on rock foundations shall be carried out in accordance with the relevant provisions of the "Guidelines for the Design of Concrete Face Rockfill Dams" (DL5016-93).
5.5 Connection between dam body, foundation and bank slope
5.5.1 The dam body fill shall be well connected with the foundation and bank slope, and the following situations shall not occur: (1) Seepage water scours along the contact surface between the dam body and the dam foundation; (2) Formation of weak surfaces, affecting the stability of the dam body; (3) Uneven settlement and cracks.
5.5.2 Before the dam body is filled, the dam foundation and bank slope shall be cleaned according to the following requirements: remove the grass, tree roots, cultivated soil and rocks on the foundation and bank slope within the dam section. Treat wells, caves, test pits, boreholes, etc.
The connection between the earth-rock dam impermeable body and the rock foundation and the bank slope should be cleared of loose stones on the surface, soil accumulation in the concave area and protruding rocks. The impermeable body should be in contact with the rock surface. If the bedrock fissures are developed, a concrete cover plate, cement mortar or concrete spraying should be installed along the contact surface between the bedrock and the dam impermeable body to separate the bedrock from the impermeable body. If necessary, the bedrock should be grouted. 5.5.3 The rock slope should be as smooth as possible and should not be stepped, reverse slope or suddenly change slope. When the bank slope is gradually steep, the slope change angle of the protruding part should be less than 20°.
The rock bank slope in contact with the impermeable body should not be steeper than 1:0.5, and the soil bank slope should not be steeper than 1:1.5. The slope of the contact surface between the impermeable body and the concrete building should not be steeper than 1:0.25.
At the connection between the permeable material of the dam shell and the bank slope, there is no special regulation for the contact slope, but the bank slope should be able to maintain its own stability. 5.5.4 At the connection between the soil impermeable body and the bank slope, the cross-section of the impermeable body should be enlarged or the downstream anti-filtration layer should be thickened. 5.5.5 The foundation cover layer or the filling material of the rock cracks in the bank slope and the permeable dam shell should meet the anti-filtration requirements, otherwise an anti-filtration layer should be set. 6.1 Top super height
6 Dam structure
6.1.1 Dam top super height refers to the height of the dam top above the static water level (normal operation or emergency operation). The dam top super height is determined by the following formula:
Where Y is the super height of the dam top above the static water level, m; R is the maximum climbing height of wind and waves along the dam slope, m, determined by calculation; A is safe heightening, m, A=0.50m is taken for normal operation and A=0.30m is taken for emergency operation. 6.1.2 The dam crest elevation shall be calculated according to the following conditions, and the maximum value shall be taken. (1) Normal water storage level or design flood level plus dam crest superelevation under normal operation (2) Check flood level plus dam crest superelevation under emergency operation: (3)
Normal water storage level plus dam crest superelevation under emergency operation plus earthquake surge height. 6.1.3 In earthquake zones, the earthquake surge height may be 0.5 to 1.0 m according to the design intensity and the water depth in front of the dam. 6.1.4 The dam crest elevation at completion shall reserve settlement. The settlement shall be determined by calculation or analogy based on the properties of the dam foundation and dam body materials. In earthquake zones, the reserved settlement may be appropriately increased. (6.1.1)
6.1.5 When a stable, strong, impermeable wave-breaking wall is provided on the upstream side of the dam crest and is closely integrated with the dam's impermeable body, the wave-breaking wall may be used to resist wind and waves, and the dam crest superelevation may be the height difference from the static water level to the top of the wave-breaking wall. However, under normal operation, the dam crest should be at least 0.5m above the static water level; under extraordinary circumstances, the dam crest should not be lower than the static water level. The height of the wave-breaking wall (the part above the dam crest) can be 1.0 to 1.2m. 6.1.6 The design wind speed used to calculate wave run-up should be based on the maximum wind speed data measured during the full reservoir period in previous years, and should be adopted in accordance with the following provisions: (1) Under normal operation conditions, 1.5 times the average maximum wind speed over many years should be adopted; (2) Under extraordinary operation conditions, the average maximum wind speed over many years should be adopted. If the wind speed of a land station is used, it should be corrected to the wind speed 10m above the corresponding reservoir water level with reference to relevant data. If there is no actual wind speed data in the local area, the wind speed can be estimated according to the wind force table and the wind force that has occurred in the area, and the wind and wave calculation can be carried out. In coastal areas, the conditions where the flood level and the maximum wind and waves occur at the same time should be considered. 6.1.7 The wave height can be calculated using the Putian Experimental Station formula or the Guanting-Hedi formula, and then the wave run-up can be calculated based on the upstream dam slope and slope protection conditions.
6.2 Dam crest structure
The width of the dam crest is determined based on the following factors:
When there is a traffic requirement on the dam crest, the road width should be determined according to highway standards; (1)
The width of the dam crest should meet the requirements for equipment passage during construction and operation and maintenance: (2)
For core wall dams or inclined wall dams, the width of the dam crest should be able to meet the layout requirements of the core wall, inclined wall and filter transition layer: (3)
In cold areas, the thickness of the protective soil layer on the upper and downstream sides of the clay core wall or inclined wall should be greater than the local frozen soil depth. (4)
The width of the dam crest can be 3 to 6 meters.
6.2.2 The design of the wave-breaking wall shall meet the following requirements: (1) The wave-breaking wall may be constructed with masonry or precast concrete blocks; the wave-breaking wall shall be sufficiently strong;
(3) Expansion joints shall be provided on the wall body;
The bottom of the wave-breaking wall shall be closely connected with the impermeable body, and the expansion joints of the wave-breaking wall of the concrete face rockfill dam shall be provided with water stops. 6.2.3
A curbstone shall be provided on the downstream side of the dam top surface. In combination with dam drainage, a drainage outlet shall be provided on the curbstone. If conditions permit, lighting equipment may be provided on the upstream side of the dam top. The dam top pavement may be made of crushed stone, sand and gravel or slag oil. The dam top pavement may be inclined 2% to 3% upward and downstream respectively. When a wave-breaking wall 6.2.4
is provided, it shall only be inclined downstream.
6.3 Dam slope
6.3.1 The dam slope should be determined based on the following factors: dam type and height;
physical and mechanical properties of the dam body and dam foundation materials; (3)
loads borne by the dam body;
construction conditions and application conditions.
In the design, the dam slope can be initially proposed by analogy with the experience of existing projects, and then the dam slope stability calculation can be carried out to ensure that the determined dam slope meets the stability requirements. 6.3.2 The upstream and downstream dam slopes can be determined according to needs to determine whether to set up a horseway, the width of which shall not be less than 1.0m, and the height difference of each horseway can be 8 to 12m. 6.4 Seepage-proof body
6.4.1 The cross-sectional dimensions of earthen seepage-proof body shall meet the following requirements: control the seepage volume within the permissible range and meet the seepage stability requirements; (1)
meet the construction requirements;
(3) the connection between the seepage-proof body and the dam foundation, bank slope or concrete structure shall meet the anti-seepage requirements; (4) be economical and reasonable.
6.4.2 The earthen seepage-proof body shall gradually thicken from top to bottom, and the top width shall not be less than 1.5m; the bottom thickness may be determined according to the permissible seepage gradient in Article 5.1.5, but the thickness shall not be less than 3.0m.
6.4.3 When geomembrane is used as the seepage-proof body, a protective layer shall be laid on the geomembrane, and a supporting layer shall be set below it. The protective layer is divided into a surface layer and a cushion layer. The protective layer shall be able to protect the geomembrane from ultraviolet radiation. The supporting layer shall ensure that the geomembrane is subjected to uniform force and is protected from damage by local concentrated stress. 6.4.4 The anti-seepage geomembrane should form a closed anti-seepage system with the dam foundation, bank slope or other concrete buildings. The peripheral seams should be properly treated, and its structural dimensions should meet the requirements of seepage slope and deformation. 6.4.5 The top elevation of the anti-seepage body should be 0.3m or more; in case of emergency use, it should not be lower than the static water level for emergency use. If a wave-breaking wall is installed on the top of the impermeable body, the super-height of the top of the impermeable body may not be restricted by this article, but it should not be lower than the static water level for normal use. 6.5 Inverted filter layer and transition layer
6.5.1 The inverted filter principle should be met between the soil impermeable body (including homogeneous dam, core wall, inclined wall, blanket and intercepting ditch, etc.) and the dam shell drainage body or dam foundation permeable layer, otherwise an inverted filter layer should be set, or an inverted filter layer and a transition layer should be set at the same time. 6.5.2 If the inverted filter principle is not met between the dam shell and the dam foundation, an inverted filter layer should be set. 6.5.3 When several soil and stone materials of different properties are used to fill the dam body, the inverted filter principle should be followed between the soil layers. The soil and stone materials with less permeability and finer particles should be filled near the core wall or inclined wall, and the soil and stone materials with greater permeability and coarser particles should be filled near the dam slope. 6.5.4 The requirements for the filter layer are as follows:
(1) It can prevent the infiltration deformation of the protected soil. The filter layer material should be non-piping soil and its permeability should be greater than that of the protected soil, so that the infiltration water can be discharged smoothly; 2)
(3) It will not be blocked and ineffective by fine particles (d<0.1mm); (4) It is durable and stable, and its properties will not change with the passage of time and the influence of the environment during use. 6.5.5 The filter layer and transition layer should be compacted. The thickness of the filter should be determined according to the purpose of the material and the construction method. The minimum thickness of each layer of the horizontal filter layer can be 30cm, and the minimum thickness of each layer of the vertical or inclined filter layer can be 40cm. When mechanical construction is used, the minimum horizontal width is determined according to the construction machinery and construction method.
The filter layer filled on the soft soil foundation should be appropriately thickened. 6.5.6 Granular filter material shall be determined according to the following criteria: (1) The relationship between the protected soil and the filter layer shall satisfy the requirements of formula (6.5.6-1) and formula (6.5.6-2):
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