What Are Geomembranes?

The geomembrane uses a plastic film as an anti-seepage base material, and is a geotechnical anti-seepage material compounded with a non-woven fabric. The anti-seepage performance of the new material geomembrane mainly depends on the anti-seepage performance of the plastic film. Plastic films for anti-seepage applications at home and abroad are mainly polyvinyl chloride (PVC), polyethylene (PE), EVA (ethylene / vinyl acetate copolymer), and in tunnel applications, ECB (ethylene vinyl acetate modified asphalt) Mixed geomembrane), they are a kind of polymer chemical flexible materials with small specific gravity, strong extensibility, high ability to adapt to deformation, corrosion resistance, low temperature resistance, and good frost resistance.

Geomembrane is a waterproof and barrier type material based on high molecular polymer.

It is mainly divided into: Low-density polyethylene (LDPE) geomembrane, high-density polyethylene (HDPE) geomembrane and EVA geomembrane.

In view of the composite geomembrane field observations, synthetic materials have certain anti-aging ability in engineering applications, so some documents in some countries have stipulated a more graceful service life, such as the former Soviet Union BCH07-74 "Application of Earth and Rock Dam According to the Notice on Polyethylene Impervious Structure, polyethylene geomembrane can be used in buildings with a service life of less than 50 years. The conclusion of the article "Long-term properties of polypropylene composite geomembrane geosynthetics" published by Linz, Austria states: "More than 15 years of field application experience with polypropylene shows that they have high chemical and biological stability; fabrics The biggest damage is in the construction; there is no big change after laying; ... the stability can be expected for more than 100 years ^[2]

The composite geomembrane uses a plastic film as an anti-seepage base material and is a geotechnical anti-seepage material compounded with non-woven fabric. Its anti-seepage performance mainly depends on the anti-seepage performance of the plastic film. Plastic films for anti-seepage applications at home and abroad are mainly polyvinyl chloride (PVC), polyethylene (PE), and ethylene / vinyl acetate copolymer (EVA). They are a kind of polymer chemical flexible materials with a small specific gravity and extensibility. Strong, high adaptability to deformation, corrosion resistance, low temperature resistance, good frost resistance.

The service life of the composite geomembrane is mainly determined by whether the plastic film loses its anti-seepage and water-proof function. According to the Soviet National Standards, the thickness of 0.2m polyethylene film with stabilizers for hydraulic use is under clear water conditions. The working life can reach 40 ~ 50 years, and the working life under sewage conditions is 30 ~ 40 years. Therefore, the service life of the composite geomembrane is sufficient to meet the service life of dam anti-seepage requirements.

The dam of Zhoutou Reservoir was originally a core wall dam, but due to the collapse of the dam, the upper part of the core wall was disconnected. In order to solve the problem of upper imperviousness, an impervious slope wall was originally added. According to the safety demonstration analysis of the Zhoutou Reservoir dam, in order to solve the leakage weak surface and dam foundation leakage caused by multiple landslides, bedrock curtain grouting, contact surface grouting, and erosion Impervious bodies such as backfill curtains and high-spray impervious plate walls of the trap wells are formed. The upper inclined wall is covered with composite geomembrane for imperviousness, and the lower part is connected with the vertical impervious wall, up to 358.0m elevation (0.97m above the check flood level) ^.

There are many domestic manufacturers of geomembrane, and the product specifications are also varied, including one cloth and one film, one cloth and two films, two cloth and one film, two cloths and two films, and multiple cloths and multiple films. Models are 200g / m ² ~ 1000g / m ² and so on, and can also be requested by users according to their own actual conditions, and manufactured by manufacturers separately according to requirements

The composite geomembrane impervious body structure consists of a base layer, a composite geomembrane, a protective layer, and a block (or concrete) slope protection (see Figure 5.5.4.1 below). The design of each layer is as follows:

The performance characteristics of HDPE geomembrane are as follows:

1. HDPE geomembrane is a flexible waterproof material with a high permeability coefficient (1 × 10 ^-17 cm / s);

2. HDPE geomembrane has good heat resistance and cold resistance, and its use environment temperature is high temperature 110 , low temperature -70 ;

3. HDPE geomembrane has good chemical stability and can resist the corrosion of strong acid, alkali and oil. It is a good anticorrosive material;

4. HDPE geomembrane has high tensile strength, which makes it have high tensile strength to meet the needs of high-standard engineering projects;

5, HDPE geomembrane has strong weather resistance, strong anti-aging performance, can be used for a long time to maintain the original performance;

6, the overall performance of HDPE geomembrane, HDPE geomembrane has a strong tensile strength and elongation at break, so that HDPE geomembrane can be used in a variety of harsh geological and climate conditions. Strong strain force to adapt to uneven geological settlement;

7. HDPE geomembrane uses high-quality native plastic and carbon black particles without any preservatives. HDPE has been used in China to replace PVC as a raw material for food packaging bags and cling film ^[1] .

Main application of geomembrane

1. HDPE geomembrane is suitable for environmental protection and sanitation: such as landfills, sewage treatment plants, power plant conditioning tanks, industrial, hospital solid waste, etc .;

2. LDPE anti-seepage membrane is suitable for water conservancy projects: such as anti-seepage and plugging of rivers, lakes, reservoirs and dams, reinforcement, anti-seepage of canals, vertical core walls, slope protection, etc .;

3. HDPE anti-seepage membrane in municipal engineering: subway, building underground engineering, planting roof, roof garden, sewage pipe anti-seepage

4. Polyethylene impervious membrane is suitable for gardens: artificial lakes, river channels, cisterns, the bottom of ponds, slope protection, green lawns, etc.

5. High-density polyethylene geomembrane is suitable for petrochemical: anti-seepage in chemical plants, oil refineries, storage tanks, linings of chemical reaction tanks, sedimentation tanks, secondary linings, etc .;

6. Polyethylene geomembrane is suitable for mining: washing tank, heap leaching tank, ash yard, dissolution pond, sedimentation pond, storage yard, tailings' bottom liner, etc.

7. Low-density polyethylene film is suitable for transportation facilities: road foundation reinforcement and seepage prevention of culverts;

8. LDPE anti-seepage membrane is suitable for agriculture: anti-seepage of reservoirs, drinking water ponds, water storage ponds, and irrigation systems;

9. HDPE film is suitable for aquaculture industry: intensive, industrialized aquaculture ponds, fish ponds, shrimp linings, sea cucumber circle slope protection, etc .;

10. High-density polyethylene impervious membrane is suitable for salt industry: salt field crystallization pond, brine pond cover, salt film, plastic pond film in salt pond ^[2] .

Geomembrane construction method

Do not drag or harden the geomembrane during transportation to avoid sharp objects stabbing.

1. It should extend from the bottom to the high position, do not pull too tight, and leave a margin of 1.50% to prepare for local sinking and stretching. Taking into account the actual situation of the project, the slope is laid from top to bottom;

2. The longitudinal joints of two adjacent panels should not be on a horizontal line and should be staggered by more than 1m from each other;

3. Longitudinal joints should be more than 1.50m away from dam feet and bend feet, and should be set on the plane;

4. Slope first and bottom of field;

5. When laying the slope, the direction of the film exhibition shall be substantially parallel to the maximum slope line.

Geomembrane laying

1. Before the geomembrane is laid, the corresponding acceptance certificate of civil engineering shall be provided.

2. Before cutting the geomembrane, the relevant dimensions should be accurately measured, and then cut according to the actual situation. Generally, it is not suitable to cut according to the size shown in the figure. It should be numbered one by one and recorded on the special form.

3. When laying the geomembrane, the welds should be minimized, and the raw materials should be saved as much as possible while ensuring the quality. At the same time

Easy to guarantee quality.

4. The overlap width of the seam between the film and the film is generally not less than 10cm. Generally, the direction of the weld seam is parallel to the maximum slope, that is, arranged along the slope direction.

5. Usually at the corners and deformed sections, the joint length should be as short as possible. Except for special requirements, on slopes with a slope greater than 1: 6, within 1.5 meters from the top slope or the area of stress concentration, as far as possible, no welds are provided.

6. During the laying of the geomembrane, artificial wrinkles should be avoided. When the temperature is low, it should be tightened and laid as far as possible.

7. After the geomembrane is laid, walking on the surface of the membrane and moving tools should be reduced as much as possible. Anything that can cause harm to the anti-seepage membrane should not be placed on the membrane or carried on the membrane. Causes accidental damage ^[2] .

Specification for geomembrane welding

Geomembrane construction effect and practical effect

Specification for geomembrane welding

I. Process flow Foundation excavation Make lake bottom mortar protection layer (H20-30mm)

Slope cutting, compacting and leveling

Composite geomembrane and vertical retaining wall

Basic leveling, clearing, process transfer

Sealed water stop for underwater water nozzle

Laying and welding of composite geomembrane

Process transfer

Welding and repair quality acceptance

Completion acceptance

Project Overview

1. Maximum design water level: about 0.6m.

2. The total area of waterproof construction is about 800 square meters.

3, ceramsite brick masonry retaining wall.

4. There are collapse pits underwater.

Third, the main waterproof material

1. Composite geomembrane coil, specifications: 50 * 4m; 150g / / 0.5mm / 150g / .

2. GB rubber water stop.

Fourth, the basic conditions

1. After foundation formation and excavation, slope cutting, smooth rolling or compaction must be performed. Displacement and backfill of disturbed soil should be sprinkled or compacted in layers, each layer thickness 400mm.

2. Remove the materials with hidden dangers of piercing, such as bricks, stones, and tiles; glass and metal debris; branches, plant roots, and so on. There are obstacles in the cleaning site to provide the necessary laying construction conditions.

3. The installation and reservation of surrounding retaining walls, pump pits, bridge foundations, and underwater nozzles must be completed before construction of the composite geomembrane. V. Welding and laying technology

1. Welding technology

Geomembrane construction site

Weld bead overlap width: 80 ~ 100mm; the natural folds of flat and vertical planes are: 5% ~ 8%; reserved expansion and contraction amount: 3% ~ 5%; leftover material amount: 2% ~ 5%

The working temperature of hot melt welding is 280 ~ 300 ; the traveling speed is 2 ~ 3m / min; the welding form is double bead. Repair method of damaged parts, cutting the same specifications of materials, hot-melt adhesive repair, polyethylene seal.

There is no imitation cloth connection at the weld bead and mechanical stitching is adopted.

The seal of the underwater nozzle is water-proof, sealed with GB rubber water-proof strip, metal bandaged and anti-corrosive treatment.

2.Laying technology

The direction of laying and unfolding of the composite geomembrane is from E to W or from W to E. Each laying length is completed once including the height of the retaining walls on both sides. The laying sequence is advanced from the axis of the channel to both sides S and N.

In the construction process, first make a mortar protective layer (20-30mm) of the composite geomembrane at the bottom of the lake, and then paste it with the vertical retaining wall.

Adhesive technology of composite geomembrane and retaining wall. Brush the adhesive on the adhesive surface of the composite geomembrane and the retaining wall, dry for about 5 minutes, and then paste, squeeze, and flatten. The adhesive is made by mixing asphalt emulsion paint, cement and water. After the paste is completed, the bolts are anchored above the water level line and waterproofed and anticorrosive.

Six, quality acceptance

1. The material and construction of composite geomembrane shall comply with the national standards for polyethylene geomembrane and composite geomembrane issued by the State Bureau of Quality and Technical Supervision.

2. Construction quality acceptance is divided into construction unit self-inspection and contractor unit random inspection.

3. Welding quality inspection adopts "inflation pressure method", and damage repair uses "visual inspection method". The inflation pressure detection index is 0.06Mpa.

4. The quality acceptance process includes procedures for handover procedures, completion acceptance, etc.

5. Normal leakage of artificial lake: 15mm / 24h (including seasonal evaporation loss).

Construction progress

1. Daily efficiency. The daily construction area of a unit is 2000 ~ 2500.

2. The planned duration is 3 days.

Suggestions

1. Strengthen the protection and management of the finished product of composite geomembrane, improve the waterproofing awareness of relevant construction personnel, and put into normal operation on schedule to ensure the quality of the project. It is of great significance.

2. It is recommended that the contractor notify and send a special person to supervise the construction personnel related to the waterproof material and find that the composite geomembrane is damaged, and the waterproof construction personnel should be notified in time for repair.

3. The composite geomembrane must be prevented from being oily, otherwise the bonding strength will be reduced. Storage and protection "see Introduction to geomembrane construction method".

4. It is recommended that the project pay attention to the following links:

After the composite geomembrane is welded to a finished product, a lake bottom mortar protective layer must be made first.

The bridge foundation is waterproof, and the reinforcement steel through-membrane welding method is adopted, and the mortar protective layer is used to prevent hidden quality problems caused by electric welding.

The adhesion of composite geomembrane to the wall must prevent the appearance of large-area hollow drums ^[1] .