SL/T 225-1998 Technical specification for application of geosynthetics in water conservancy and hydropower engineering SL/T 225-98
Some standard content:
Industry Standard of the People's Republic of China
Technical Specification for Application of Geosynthetics in Hydraulic and Hydro-power Engineering
Standard for applications of geosynthetics inhydraulic and hydro-power engineeringSL/T225--98
Editor: Beijing Graduate School of North China University of Water Resources and Hydropower Approval department: Ministry of Water Resources of the People's Republic of China Effective date: November 15, 1998
Ministry of Water Resources of the People's Republic of China
Notice on Approval of Issuance of "Technical Specification for Application of Geosynthetics in Hydraulic and Hydropower Engineering" SL/T225--98 Water Resources Department [19987482]bzxZ.net
According to the formulation and revision plan of water conservancy and hydropower technical standards of the Ministry of Water Resources, the "Technical Specification for Application of Geosynthetics in Hydraulic and Hydropower Engineering" formulated by the International Cooperation and Science and Technology Department of the Ministry of Water Resources and the Beijing Graduate School of North China University of Water Resources as the main editor has been reviewed and approved as a recommended water conservancy industry standard and is hereby issued. The name and number of the standard are: "Technical Specification for Application of Geosynthetics in Water Conservancy and Hydropower Engineering" SL/T225-98. This standard has been implemented since November 15, 1998. During the implementation process, all units should pay attention to summarizing experience.
This standard is interpreted by the International Cooperation and Science and Technology Department of the Ministry of Water Resources. The standard text is published and distributed by China Water Conservancy and Hydropower Press. October 10, 1998
This standard is compiled according to the Ministry of Water Resources' water conservancy and hydropower technical standard formulation and revision plan. The content of this standard includes the design method of using geosynthetics for anti-filtration, drainage, anti-seepage, bank protection, anti-scouring, and soil reinforcement and reinforcement, as well as the key points of construction technology.
During the compilation process, the compilation team conducted extensive investigations and studies, carefully summarized the engineering practice experience in relevant fields in my country, and referred to relevant national standards, industry standards and foreign advanced experience; on the basis of listening to the opinions of many domestic experts, after careful revision, this standard was completed.
It is hoped that all units will continue to accumulate information and summarize experience in the process of adopting this standard. Please inform the editor-in-chief of the need for amendments and supplements.
The department in charge of this specification: International Cooperation and Science and Technology Department of the Ministry of Water Resources The editor-in-chief of this specification: Beijing Graduate School of North China Institute of Water Resources and Hydropower The co-editor of this specification: China Geosynthetics Engineering Association Ministry of Railways Scientific Research Institute
The main authors of this specification: Wang Zhenghong Yang Canwen Wang Yuren Peng Yijiang Dou Baosong 21
1 General Provisions
1.0.1 In order to make the use of geosynthetics in water conservancy and hydropower projects advanced, safe, reliable, economical and reasonable, and to ensure quality, this specification is specially formulated. 1.0.2 This specification applies to the following sub-projects of water conservancy and hydropower projects: filter layer, drainage, anti-seepage, protection and soil reinforcement. It focuses on design and also describes construction.
1.0.3 When geosynthetics are used for design and construction, in addition to complying with this specification, they shall also comply with the provisions of other relevant national specifications and standards in force.
2 Terms and symbols
2.1 Terms
2.1.1 Geosynthetics. A general term for synthetic materials used in geotechnical engineering. 2.1.2 Geotextiles. Permeable geosynthetics. According to different manufacturing methods, they are divided into woven geotextiles and non-woven geotextiles. 2.1.3 Woven geotextiles. Cloth-like rolls woven from monofilaments or multifilaments, or from flat yarns formed by films. 2.1.4 Non-woven geotextiles. Cloth-like rolls made of short fibers or spun filaments in random arrangement, mechanically entangled (needle punching), or thermally bonded, or chemically bonded.
2.1.5 Geotextile mold bags. A continuous flat bag-like structural material with different spacing (thickness) made of double-layer chemical fiber fabric (woven type). It is filled with concrete or cement mortar and forms a plate-like protective block after solidification. 2.1.6 Geomembrane. A relatively impermeable roll made of polymer or asphalt. The former is manufactured in the factory by blow molding, calendaring or coating; the latter is formed on site or in the field by spraying or dipping. 2.1.7 Geogrid. The polymer sheet is punched and stretched in one direction or two directions to form a tensile material with a strip grid or rectangular grid shape. 2.1.8 Geonet. A flat structural mesh material with larger holes and a certain rigidity made by extruding a polymer into a net, or weaving thick strands, or pressing synthetic resin.
2.1.9 Geotextile belt. A strip tensile material made by extrusion and stretching, or compounding with reinforcement materials. 2.1.10 Three-dimensional vegetation geonet. A three-dimensional mesh structure made of polymers through hot extrusion, stretching and other processes. The bottom is a high modulus base layer, covered with a foamed and bulky net bag, filled with fertile soil and grass seeds for plant growth. 2.1.11 Plastic drainage belt. A drainage material composed of a strip core material with different concave and convex cross-sectional shapes to form a continuous drainage trough, and a non-woven geotextile wrapped on the outside.
2.1.12 Geocomposite materials. Materials formed by compounding or combining two or more geosynthetics. For example, geomembranes and geotextiles are heated and rolled to form various composite geomembranes. 2.1.13 Equivalent pore size. The apparent maximum pore size of the fabric. 2.1.14 Gradient ratio (GR). The ratio of the hydraulic gradient of water flowing vertically through the geotextile and the 25mm thick soil layer to the hydraulic gradient through the overlying 50mm thick soil layer.
Aa—Area
B---Width
Cohesion
Cu-—Unevenness Coefficient
Consolidation Coefficient
D, d-—Particle Size
-Eccentricity
Fs——Safety Factor
fFriction Coefficient
Gravity Acceleration
H-Height
J,-—Hydraulic Gradient
K-—Earth Pressure Coefficient
——Permeability Coefficient
L-—Length
M-Bending Moment
-Volume Compression Coefficient
N,n-—Number, Coefficient
N. ,N--Bearing Capacity Factor
Og5——Equivalent Aperture
P. -Active earth pressure
Pp-Passive earth pressure
Q-Flow
q-Ultimate bearing capacity
R-Radius
s-Seconds
T-Tensile strength
-Allowable tensile strength
U-Consolidation degree
-Speed
W-Weight
Water content
-Arm
a, p-
-Angle, coefficient
1. Thickness
Water conductivity, coefficient
Normal stress
Shear stress, shear force
Friction angle
1. Water permeability
3. Materials and performance tests
3.1 General provisions
3.1.1 The raw materials of geosynthetics products mainly include polypropylene (PP), polyethylene (PE), polyester (PER), polyamide (PA), high-density polyethylene (HDPE) and polyvinyl chloride (PVC). 3.1.2 Geosynthetics include the following four categories: geotextiles, geomembranes, geotechnical special materials and geocomposite materials. Woven type
(divided into round yarn)
Geotextile
Non-woven type
Flat weave
(knitted
{needle punched
(divided into long and short fibers)
(adhesive
Geosynthetic geomembrane
Composite materials
There are different materials, thicknesses, and different methods of blowing, calendering, coating, and roughening of the membrane surface. Geogrids, geobelts, geocells, geonets, geogabbers, geotechnical special materials (Guigong pipes, main mold bags, three-dimensional mesh pads, styrene, etc. [Composite geomembranes - geomembranes and fabrics or other materials are combined with geocomposite materials
[Composite drainage materials - drainage belts, drainage pipes, drainage and waterproof materials, etc. 3.2 Performance indicators and their tests
3.2.1 Geosynthetics Material indicators include their own characteristic indicators and indicators of interaction with soil (performance indicators). The latter is the reaction when interacting with soil, which should simulate actual working conditions and be determined by experiments. 3.2.2 The indicator determination test includes the following main items: 1 Physical indicators. Unit area mass, thickness, equivalent aperture (EOS) and its relationship with pressure), etc. 2 Mechanical indicators. Tensile strength, tear strength, holding strength, bursting strength, bursting strength, friction strength of interaction between materials and soil, etc.
3 Hydraulic indicators. Vertical permeability coefficient (or permeability), plane permeability coefficient (or hydraulic conductivity), gradient ratio (GR), etc. 4 Durability. Anti-aging, anti-chemical corrosion. 3.2.3 Select the test items of the material according to the specific needs of the project. The test method should comply with relevant standards. 3.2.4 When determining the design index, the influence of environmental changes on the parameters should be considered. For example, non-woven geotextiles become thinner under pressure, and the equivalent pore size and permeability are reduced accordingly.
3.2.5 When the measured ultimate tensile strength T is used for design, it should be reduced according to formula (3.2.5); the specific value can be taken according to the provisions of Table 3.2.5. T.=FoF.RFoF.T
Where T. is the allowable tensile strength of the material, kN/m; T is the ultimate tensile strength, kN/m,
FiD is the coefficient of mechanical damage during laying; FcR is the coefficient of material change;
FeD is the coefficient of chemical damage; FD is the coefficient of biological damage. 24
Scope of application
Bearing capacity
Slope stability
Note 1. For temporary projects, the smaller value is taken.
Table 3.2.5 The lowest influence coefficient of geotextile strength
2. The coefficient product (FipFcR FpFbD) should be 2.5 ~ 5.0. 2.0~4.0
1.0~~1.5
1.0~~1.5
3.2.6 The tearing strength, holding strength, bursting strength, bursting strength and joint strength of the material should also meet the requirements of Article 3.2.5.
Woven geotextiles are used for reinforcement of non-cohesive soil. In the absence of actual friction strength measurement data, the friction angle between the fabric and the soil can be 9/3 of the internal friction angle Φ of the soil material.
3.3 Acceptance, transportation and storage of materials
3.3.1 When using geosynthetics, the test report of the test unit should be inspected. The user shall conduct sampling inspection, and the sampling rate shall be more than 5% of the number of delivered rolls, and shall not be less than 1 roll at least. The content shall be in accordance with the contract. 3.3.2 When delivering, the product shall be labeled with the manufacturer, number, production date and product specifications, etc. It shall not be directly exposed to sunlight during transportation, and shall be covered or packaged.
3.3.3 When storing the product, it must be protected from sunlight; away from fire sources; the storage period shall not exceed the validity period of different products. 3.3.4 Before starting the next process after each construction process is completed, the construction stage acceptance shall be carried out in accordance with the regulations. Filter and drainage
4.1 General provisions
4.1.1 Geosynthetics can replace traditional granular materials to build filter layers and drainage bodies. 4.1.2 When non-woven geotextiles are used as filter materials, their unit area mass and thickness shall meet the engineering requirements. When following reciprocating water flow, thicker fabrics should be used.
4.1.3 When the drainage capacity of the non-woven geotextiles used is insufficient, other composite drainage materials can be used. 4.1.4 Geosynthetics can be used in the following parts of water conservancy and hydropower projects: 1 Transition layer on the inclined wall, core wall and downstream side of earth-rock dam. 2 Vertical drainage body in dam body.
3 Drainage body downstream of embankment.
4 Filtration layer on embankment slope.
5 Drainage body around drainage corridor
6 Drainage and exhaust layer under blanket.
Outer enclosure of culvert drainage.
8 Drainage body behind bank wall and pier.
Protection body of sluice bottom plate joint and outflow. 25
10 Drainage body behind lining of hydraulic tunnel.
11 Outer enclosure of drainage pipe, pressure relief well and agricultural well. 4.2.1 Anti-filtration materials shall meet the following requirements: 4.2 Anti-filtration criteria
1 Soil retention. Prevent the loss of protected soil and cause seepage deformation. 2 Water permeability. Ensure smooth discharge of seepage water. 3 Anti-blocking property. Ensure that it will not be blocked by fine soil particles and become ineffective. 4.2.2 The soil retention of geotextiles should be characterized by the relationship between the equivalent pore size of geotextiles and the characteristic particle size of soil. The equivalent pore size should meet the conditions of formula (4.2.2-1):
Ogsndgs
-equivalent pore size of geotextiles, mm;
Where O95---
(4.2.2-1)
dss-characteristic particle size of the protected soil, that is, the mass of soil smaller than this particle size accounts for 85% of the total mass, and the smallest dss in the sample is used, mm;
The empirical coefficient related to the type, gradation, fabric variety and state of the protected soil shall be adopted according to the provisions of Table 4.2.2. n
Table 4.2. 2 Coefficient n
Content of fine particles in protected soil
(d≤0.075mm) (%)
Soil non-uniformity coefficient,
or geotextile type
2≥Cu,Cu≥8
4≥C>2
Woven fabrics
Non-woven fabrics
Note: When it is expected that the buried geotextile and the soil particles below it may move, the value of n should be 0.5. The soil non-uniformity coefficient Cu should be calculated according to formula (4.2.2-2): d6o
0g≤0.3mm
--the mass of soil smaller than each particle size in the soil accounts for 60% and 10% of the total soil mass respectively. In the formula, dgodio-
4.2.3 The water permeability of geotextiles shall meet the following conditions: 1 When the protected soil is well graded, the hydraulic gradient is low and silting is not expected (clean sand, medium-coarse sand, etc.): k≥k.
2 When drainage failure leads to damage to soil structure, high repair costs, high hydraulic gradient, and complex flow pattern: kg≥10ks
In the formula, k, k. — Permeability coefficient of geotextile and protected soil, cm/s. 4.2.4 The anti-blocking property of geotextiles requires that its pore size shall meet the following conditions: 1 When the protected soil is well graded, the hydraulic gradient is low, the flow pattern is stable, the repair cost is low, and silting is not expected, O≥3drs
In the formula, dis——the characteristic particle size of the protected soil, that is, the mass of soil smaller than this particle size accounts for 15% of the total soil mass, mm. For other symbols, see the formula of this specification (4.2.2-1). 2 When the protected soil is prone to pipe bursts, has dispersion, high hydraulic gradient, complex flow pattern, and high repair costs: (1) When the permeability coefficient of the protected soil is k. ≥ 10-scm/s: GR ≤ 3
(4.2.2-2)
(4.2.3-1)
(4.2.3-2)
(4.2.4-1)
(4.2.4-2)
Where GR is the gradient ratio, the test method is as follows: (2) When the permeability coefficient of the protected soil is k, < 10-5cm/s, a long-term siltation test should be carried out on site soil materials to observe the siltation situation, the test method is as follows:
4.3 General design method
4.3.1 The design should have the following basic information: 1 The soil type to be protected or used as drainage material, particle analysis curve, permeability coefficient, shear strength index and chemical composition of the soil.
2 The equivalent pore size Og5 of the geotextile, the vertical permeability coefficient k, the horizontal permeability coefficient kh, the relationship between the permeability coefficient and the normal pressure, etc. 4.3.2 Check the selected geotextile with the anti-filtration criterion: 1 Soil retention. It should be verified according to formula (4.3.2-1). 2 Water permeability. The water permeability provided by the geotextile and the required water permeability should be calculated according to formula (4.3.2-1) and formula (4.3.2-2), and judged according to formula (4.3.2-3).
In the formula, k, — vertical permeability coefficient of geotextile, cm/s; — thickness of geotextile, cm;
estimated flow rate, cm\/s,
head difference on both sides of geotextile, cm,
A — water flow area of geotextile, cm,
F, — safety factor, should be not less than 3.
3 Anti-blocking. It should be checked according to the provisions of 4.2.4 of this code. 4 Geotextiles should meet the above three criteria. (4.3.2-1)
(4. 3. 2-2)
(4.3.2-3)
4.3.3 When geotextiles are used for drainage, in addition to meeting the requirements of 4.3.2, the plane water conductivity of the geotextile should also be calculated. The water conductivity of the geotextile and the water conductivity required to meet the plane drainage. 1 The hydraulic conductivity 6. and 6, should be calculated according to formula (4.3.3-1) and formula (4.3.3-2): e,kno
2 The hydraulic conductivity of geotextiles should meet the requirements of formula (4.3.3-3): .≥F.0.
Wherein 8.—hydraulic conductivity of geotextiles, cm/s; O,-—hydraulic conductivity required for drainage, cm\/s; -—thickness of geotextiles, cm;
qt-——single width flow, cm\/s,
kh—plane permeability coefficient of geotextiles, cm/s; i-hydraulic gradient at both ends of geotextiles.
3 When it does not meet the requirements of 1 and 2, other composite drainage materials can be used. (4.3.3-1)
(4.3.3-2)
(4.3.3-3)
4.3.4 When laying geotextiles on the slope, an anti-sliding stability analysis should be conducted, and the safety factor should meet the requirements of relevant specifications. 4.3.5 Surface protection structure. In order to ensure that the anti-filtration and drainage system always maintain normal operation, surface protection and fabric fixing measures should be taken. 27
1 There is coarse material under the geotextile. To prevent the fabric from being punctured, gravel with a thickness of 10cm should be laid first, and then the fabric should be laid after leveling. 2 A gravel protective layer should be provided on the geotextile. 3 The geotextile should be buried in the anchor trench at the top and toe of the slope, and the trench depth should not be less than 30cm, as shown in Figure 4.3.5-1; at the foot of the river bank, in order to prevent scouring, the geotextile should be extended and folded back to make a pressure pillow, as shown in Figure 4.3.5-2, and the pressure pillow should reach below the scouring line. >2m
Figure 4.3.5-1 Geotextile top slope reinforcement
1—Protective layer; 2—Geotextile 13—Earth slopeFigure 4.3.5-2 Slope toe anti-scour structure
1—Protective layer; 2—Geotextile; 3 Earth slope
4.4 Design of vertical drainage body in dam
4.4.1 When a vertical drainage body is used in a homogeneous earth dam, it can be inclined upstream or downstream, and the bottom is connected to a horizontal drainage cushion to guide the seepage water outside the dam. The position and size of the drainage cushion shall comply with the requirements of relevant specifications. 4.4.2 Verify the anti-filtration criteria of geotextiles. It should be carried out in accordance with the requirements of 4.2 of this specification. 4.4.3 Estimation of water inflow. The schematic diagram of the vertical drainage body in the dam is shown in Figure 4.4.3. The water inflow can be estimated by the flow net. The flow of the geotextile drainage body gradually increases from top to bottom, and the required discharge flow should be estimated in sections. H
Figure 4.4.3 Schematic diagram of drainage in the dam
1 Water surface, 2 Core wall: 3-Vertical drainage 4-Horizontal drainage 4.4.4 Verify the planar water conductivity of geotextiles. The water conductivity and 6t shall be calculated section by section along the drainage body from top to bottom according to formula (4.3.31) and formula (4.3.3-2) of this code.
1 The hydraulic gradient i in formula (4.3.3-2) shall be calculated according to formula (4.4.4-1): i=sinβ
Where β is the inclination angle of the vertical drainage body. 2 The section by section verification shall meet 6.≥F.6., otherwise a thicker fabric shall be replaced, or other composite drainage materials shall be used. (4.4.4-1)
4.4.5 Calculation of downstream horizontal drainage cushion layer. The calculation of the water conduction capacity of the cushion layer shall be carried out in accordance with the provisions of Articles 4.4.2 and 4.4.3 of this Code. The drainage volume shall be the sum of the maximum flow at the bottom of the vertical drainage and the flow from the foundation into the horizontal cushion layer. The flow from the foundation shall be estimated in accordance with the relevant specifications.
4.5 Construction points
4.5.1 The construction of geotextile filter layer and drainage body includes the following procedures: leveling and rolling site, fabric preparation, laying, backfilling and surface protection. 4.5.2 Leveling and rolling site. All hard objects with sharp edges that may damage the geotextile on the ground should be removed, pits should be filled, the soil surface should be leveled, or the slope should be repaired.
4.5.3 Preparation of materials. Cut and splice according to the requirements of the project; the fabric should be protected from damage and kept free from dirt. 28
4.5.4 Laying. The following requirements should be met:
1 It should be smooth, moderately tight, and not too tight; the fabric should be close to the soil surface without leaving any gaps. 2 If the fabric is found to be damaged, it should be repaired or replaced immediately. 3 Adjacent fabric blocks can be spliced by overlapping or sewing. Generally, overlapping can be used. The overlap width on flat ground can be 30cm, and the overlap width on uneven ground or extremely soft soil should be no less than 50cm; underwater laying should be appropriately widened. 4 When it is expected that the fabric may undergo large displacement during work and cause the fabric to be pulled apart, sewing should be used. See Figure 4.5.4 for the sewing form. [>40
(a) Flat joint
(b) Butt joint
(c) J-shaped joint
Figure 4.5.4 Joint form (dimension unit: mm) (d) Spiral joint
5 When there is reciprocating water flow, it is advisable to lay a 5-10cm thick sand layer under the fabric. At this time, it is not suitable to overlap to prevent sand from entering the gap and separating the fabric. When there is a dynamic load, the sand layer should also be laid first. 6 When laying in flowing water, the upstream fabric block at the overlap should cover the downstream block. 7 Slope laying should generally be carried out from bottom to top. The top and foot of the slope should be fixed with anchor trenches or other reliable methods to prevent them from sliding. 8 Laying workers should wear soft-soled shoes to avoid damaging the fabric. 9 After the fabric is laid, it should be avoided from direct sunlight. Fill as you lay, or take protective measures. 10 There should be no gaps at the connection with the slope structure, and the combination should be good. 4.5.5 Backfilling should meet the following requirements:
1 The backfill material shall not contain substances that are detrimental to the fabric. 2 When backfilling, the geotextile shall not be damaged. Only when there is a loose soil cushion layer of at least 30cm thick on the geotextile can it be lightly compacted. Heavy machinery or vibration rollers shall not be used for compaction.
3 The compaction degree of the backfill material shall meet the design requirements. 5 Waterproof
5.1 General provisions
5.1.1 For high head (greater than 50cm) water retaining structures, the use of geomembranes for anti-seepage should be demonstrated. 5.1.2 The geosynthetics used for anti-seepage mainly include geomembranes and composite geomembranes. Their thickness should be determined according to the specific base conditions, environmental conditions and the properties of the geosynthetics used. For anti-seepage structures that bear high stress, reinforced geomembranes should be used. In order to increase the friction coefficient of the surface layer, composite geomembranes or geomembranes with roughened surfaces can be used. 5.1.3 In order to prevent the geomembrane from being damaged by water and air, drainage and exhaust measures should be taken. Generally, geotextile composite geomembranes can be used. When a large amount of water and air is expected, special discharge measures should be set up according to the situation. 5.1.4 The following parts of water conservancy and hydropower projects can consider the use of geomembranes for anti-seepage: 1 dike, dam core wall, inclined wall.
2 dike and dam horizontal covering.
3 Vertical anti-seepage walls for dike and dam foundations.
4 Heightening of earth dams.
Anti-seepage for upstream surfaces of rockfill dams, face dams, masonry dams and roller-compacted concrete dams. 5
Anti-seepage lining for channels and reservoirs.
7 Construction of anti-seepage walls for cofferdams.
8 Underflow interception in river channels.
9 Anti-seepage for hydraulic tunnels.
5.1.5 The anti-seepage design for channels shall comply with SL18-91 Technical Specifications for Anti-seepage Engineering for Channels. 5.2 Anti-seepage structure of geomembrane
5.2.1 A protective layer and an upper cushion layer shall be provided on the anti-seepage geomembrane, and a lower cushion layer shall be provided below it. The schematic diagram of the anti-seepage structure is shown in Figure 5.2.1.
5.2.2 The material and structure of the protective layer shall be reasonably determined according to the type of project, importance and conditions of use.
1 The protective layer of channels, ponds, etc. can be made of compacted plain fill, gravel, prefabricated or existing Figure 5.2.1 Anti-seepage surface structure
1-Dam body; 2-Supporting layer; 3-Lower cushion layer; 4-Geomembrane layer, 5-Upper cushion layer and protective layer cast concrete slab, mortar masonry or dry masonry. 2 When the protective layer is made of rigid materials such as rockfill or concrete, an upper cushion layer should be set under the protective layer. When a composite geomembrane with geotextile is used, an upper cushion layer may not be set. 3 The specific requirements and practices of the protective layer shall comply with the provisions of the Ministry of Water Resources and Electric Power Standard SDJ218-84 "Design Specifications for Rolled Rock Dams".
5.2.3 The materials and practices of the upper cushion layer shall be determined according to the types of anti-seepage geomembrane and protective layer. 5.2.4 The lower cushion layer shall be determined according to the project type, geomembrane type and foundation conditions. 5.3 Seepage prevention design of earth-rock embankments and dams
5.3.1 The seepage prevention structure of earth-rock embankments and dams shall comply with the provisions of 5.2 of this Code. 5.3.2 The thickness of the anti-seepage geomembrane of earth-rock embankments and dams shall not be less than 0.5mm. For important projects, it should be appropriately thickened, and for minor projects, it can be appropriately thinned, but the minimum thickness shall not be less than 0.3mm. 5.3.3 There are usually several ways to lay upstream anti-seepage geomembranes, and the schematic diagram is shown in Figure 5.3.3. (a)
Figure 5.3.3 Geomembrane laying form
1—Geomembrane
1 Straight slope. Inclined wall, thin protective layer, used for low head dams; or used as core wall, or used for reinforcement of existing embankments and dams. As shown in Figure 5.3.3 (a) (b) (c).
2 Folded slope. Inclined wall, horseway is set for higher head dams, as shown in Figure 5.3.3 (f). 3 Sawtooth. Sloping wall, as shown in Figure 5.3.3 (d). 4 Step-shaped. Sloping wall, as shown in Figure 5.3.3 (e). 5.3.4 The calculation of geomembrane anti-seepage system should be verified for stability and drainage capacity behind the membrane: 1 Stability verification. Verification conditions: The verification is only for the anti-sliding stability between the protective layer, the upper cushion layer and the geomembrane. The most dangerous working condition for verification is a sudden drop in reservoir water level. The specific verification method is shown in Appendix A. The minimum safety factor required for verification should comply with the standard SDJ218-84. 2 Calculation of drainage capacity behind the membrane. The calculation is based on the flat drainage of non-woven geotextiles behind the membrane or the water conduction capacity of the sand cushion layer. When the upstream water level drops suddenly, part of the water in the dam body will flow upstream, flow along the geotextile to the bottom of the slope, and be discharged downstream through the drainage pipe or diversion ditch behind the dam. The amount of water should be estimated first, the water conductivity of each section of geotextile from top to bottom should be verified, and a certain safety factor should be considered. The specific calculation method is shown in Appendix B. 5.3.5 The design of anti-seepage for embankments can refer to the relevant provisions of this code. 5.4 Design of anti-seepage blanket
5.4.1 When the dam foundation is a permeable foundation such as gravel, geomembrane can be used to replace the traditional weakly permeable soil when the upstream blanket scheme is selected. 5.4.2 The thickness of the geomembrane should be estimated by calculation based on the working head, the width of the cracks that may occur under the membrane, the strain and strength of the membrane, etc., and estimated according to Appendix C. For medium head dams, the required thickness is generally 0.5-0.6mm. 5.4.3 The reasonable length of the blanket should limit the seepage slope and seepage volume of the dam foundation to the allowable value, determined by hydraulic calculation, and calculated according to the provisions of specification SDJ218-84. The general length is 5-6 times the working head. 5.4.4 The contact surface between the blanket and the reservoir bottom should be basically flat and should meet the anti-filtration criteria. In order to prevent pipe bursts and pits from occurring at possible cracks, geomembranes should use geotextile composite geomembranes.
5.4.5 After the reservoir is filled with water, water may still enter under the anti-seepage geomembrane, displace some air, and work together with the upward water pressure under the original membrane to make the membrane float or break, so preventive measures should be taken according to the situation. Common methods include: "check valve" (as shown in Figure 5.4.5), blind ditch and weight. When the weight method is used, the required weight added to the geomembrane is determined according to the water head under the membrane, which can be obtained through hydraulic calculation. The geomembrane can be considered impermeable during calculation. When the required weight is too large, the above two methods can be used in combination. 5.4.6 The connection between the blanket and the bank slope should comply with the provisions of the specification SDJ218-84.
5.4.7 The anti-seepage design of the reservoir area can be carried out with reference. 36
Top view
Guo Zai Dao Mi
Turn-over view
Figure 5.4.5 Check valve structure
1--Geomembrane blanket; 2-Geotextile drainage diameter 20cm, 3-Welding or bonding: 4-Saw cover plate diameter 30cm15-Concrete block, diameter 40cm16-Nylon rope; 7-Aluminum frame 5.5 Vertical waterproof
5.5.1 When the horizontal anti-seepage scheme of the foundation is not reasonable, and the buried depth of the strong permeable layer in the foundation is within the capacity of the slotting machine, the geomembrane vertical anti-seepage scheme can be considered.
5.5.2 When the foundation meets the following conditions, the geomembrane vertical anti-seepage scheme can be implemented: 1 The depth of the permeable layer is generally within 12m, or through efforts, the slotting depth can reach 16m. 2 The content of particles larger than 5cm in the permeable layer shall not exceed 10% (by weight), and the maximum particle size of a small number of large stones shall not exceed 15cm, or shall not exceed the size allowed by the slotting equipment. 3 The water level in the permeable layer shall be able to meet the requirements of mud wall consolidation. 4 When the bottom of the permeable layer is a rock hard layer, the requirements for anti-seepage are not very strict. 5.5.3 Hole-making equipment and methods:
1 When the depth of the sandy soil permeable layer without coarse particles is not more than 10m, and the clay layer above it is relatively thin, the high-pressure head hole-making and slotting method can be used to form the slot.
2 When the foundation is a strong permeable layer containing coarse particles and the overlying clay layer is relatively thin, it is advisable to use a chain bucket or hydraulic sawing machine to make slots. For vertical anti-seepage, step ethylene geomembrane, composite geomembrane or waterproof plastic board can be used. The thickness of the geomembrane should not be less than 0.5mm, and hot melt welding is adopted. 5.5.4
5.5.5 After the geomembrane is laid in the trench, the soil filling on both sides of the membrane should be carried out in time, and the longest delay should not be 24 hours to avoid wall collapse.
Tip: This standard content only shows part of the intercepted content of the complete standard. If you need the complete standard, please go to the top to download the complete standard document for free.