Utilization of composite geomembrane in water reuse pool in a thermal power plant

1 Project overview

A reclaimed water pool with a volume of more than 5500m3 is proposed to be built in a reclaimed water reuse project in a thermal power plant. On-site situation: The site is limited and irregular, with one side spacious and one side narrower and triangular. On the southwest side of the site, there is an underground river about 10m away from the site.  The volume of the pool is relatively large, and the cost of making a reinforced concrete structure pool is too high. ④ There are a lot of rubble on the site, and the local materials are used to build a rubble masonry pool, which can save investment.

In view of this, the design decided to make the middle water pool into a stone artificial lake pool, which can not only beautify the environment, but also meet the water storage requirements and reduce investment. The key is to solve the leakage, so the design adopts the anti-seepage technology of composite geomembrane.

The engineering geological conditions of the site are simple. Except for the 1m-thick fill, the bearing layer of this pool is all the same as the fractional clay.

2. Anti-seepage principle and construction process of composite geomembrane

1) Anti-seepage principle of composite geomembrane

The composite geomembrane uses plastic film as the anti-seepage base material, and is a geotechnical anti-seepage material compounded with non-woven fabrics. Its anti-seepage performance mainly depends on the anti-seepage performance of the plastic film. At present, the plastic films used for anti-seepage applications at home and abroad mainly include polyvinyl chloride (PVC) and polyethylene (PE). Corrosion, low temperature resistance, good frost resistance. The main mechanism is that the water-impermeability of the plastic film blocks the leaking channels of the soil, and it can withstand water pressure and adapt to the deformation of the soil with its large tensile strength and elongation. The chemical material, formed by needle punching or thermal bonding, has high tensile strength and extensibility. After it is combined with the plastic film, it not only increases the tensile strength and puncture resistance of the plastic film, but also increases the tensile strength and puncture resistance of the plastic film. Roughness increases the friction coefficient of the contact surface, which is beneficial to the stability of the composite geomembrane and protective layer. At the same time, they have good corrosion resistance to bacteria and chemical effects, and are not afraid of acid, alkali and salt erosion.

2) Construction process of composite geomembrane

Before the composite geomembrane is laid, the earthwork filling and slope trimming are completed, and the slope flatness and compaction meet the design requirements, and the composite geomembrane can be laid only after passing the acceptance by the supervision engineer. The composite geomembrane of this project The laying process is:

Construction equipment → laying of composite geomembrane → splicing of composite geomembrane → quality inspection → laying of upper cushion, protective layer and rubble → acceptance.

3. Construction method of composite geomembrane

1) Construction preparation

(1) Quality inspection of composite geomembrane materials, all indicators are in accordance with the requirements of composite standards and design requirements.

(2) After cleaning and leveling the embankment slope, clear all the sharp corners and debris, backfill and compact the underslope, cut the slope and excavate the rich slope and pass the inspection and acceptance, and provide a working surface for the laying of the composite geomembrane.

(3) Geomembrane splicing in the field In order to facilitate construction and ensure the quality of splicing, the composite geomembrane should be as wide as possible to reduce the amount of on-site splicing. Before construction, it should be cut according to the width and length of the composite geomembrane, and spliced ​​to meet the requirements Blocks of size, rolled on steel pipes, and manually transported to the work surface for laying.

2) Laying of composite geomembrane

(1) Laying method of composite geomembrane

When laying film, it must be laid from bottom to top. The film and the film and between the film and the base surface should be pressed flat and tight, but the film should not be pulled too tightly. Generally, it should be slightly loose, but there should be no gaps at the bottom of the film. Because the geomembrane is relatively thin and light, it is easy to be blown by the wind before the protective layer is laid after it is laid, so the area of ​​one laying membrane should not be too large.

According to the information provided by the manufacturer, the width of the composite geomembrane is 1.0m-1.9m. This project uses a width of 1.9m and a thickness of 0.6mm to reduce the material used for the joint.

(2) Technical requirements for laying composite geomembrane

The laying should be carried out in dry and sunny weather. In order to facilitate splicing and prevent stress concentration, the composite geomembrane is laid in a wave-shaped relaxation method with a margin of about 1.5%. , No protruding folds, construction workers should wear flat shoes or soft-footed shoes, it is strictly forbidden to wear spiked shoes, so as not to step on the geomembrane, if the geomembrane is found damaged during construction, it should be repaired in time.

3) Splicing of composite geomembrane

(1) This project adopts two-cloth and one-membrane composite geomembrane, and the welding adopts the hot-melt welding method. The splicing includes the seam of the geotextile and the welding of the geomembrane. For the convenience of construction, the composite geomembrane is spliced ​​at the construction site.

(2) The quality of the composite geomembrane welding is the key to the success or failure of the composite geomembrane's anti-seepage performance. Therefore, the welding of the geomembrane must be done well to ensure the welding quality. Therefore, the geomembrane welding is carried out by the manufacturer to send professional technicians to the site to operate, guide and train, and use special welding equipment for geomembrane. The geomembrane of this project is welded by ZPR-210V heat-bonding geomembrane welding machine, and the geotextile is seamed by a portable sealing machine.

(3) The welding process of the two-cloth-one-membrane composite geomembrane in this project:

Lay the film→weld film→turn the bottom layer cloth→turn the surface and lay it→sew the upper layer cloth

(4) Welding process: The first geomembrane is laid, and the edges to be welded are folded (about 600mm wide), the second one is laid on the first membrane in reverse, and the direction of the welding edges of the two membranes is adjusted to make it Lap 100mm.

(5) Before welding, use a hair dryer to remove the sand, soil and other swag on the film surface to ensure that the film surface is clean, and place a long wooden board under the welding part so that the welding machine can walk on a flat base surface to ensure the welding quality. Formal Before welding, test welding is carried out according to the construction temperature to determine the walking speed and welding temperature. Generally, the walking speed is 1.5m/s-2.5m/s, and the welding temperature is 220℃-300℃.

4) Anchorage of composite geomembrane

The quality of the anchorage is related to whether a closed anti-seepage body can be formed. The lower anchorage should be completed after the construction of this section of the anti-seepage body and approved by the supervisor. The upper part is anchored until the composite geomembrane is laid and spliced ​​on the slope surface, and the concrete pouring is completed after the construction of the protective layer.

5) Protective layer and rubble laying

The soil material of the 100mm thick protective layer of the geomembrane must be sieved, and no particles with a particle size larger than 2mm are not allowed, otherwise the geomembrane will be easily pierced. The soil material of the protective layer must be compacted and compacted to ensure that the dry bulk density is above 1.5, and sampling inspection shall be conducted at any time. When laying the protective layer and building the rubble protective surface, it must be handled with care to avoid breaking the geomembrane. Under the rubble protective surface, a 200mm thick gravel cushion is laid to prevent the soil protection layer from being scrubbed due to the influence of water level changes, wind and waves and other factors. The rubble is paved with artificial hanging lines, and the rubble should be tightly embedded.

4 Use the effect

After being put into use, the effect is good. It not only solves the leakage problem, meets the water storage function, but also has the effect of beautifying the environment, and at the same time greatly saves investment.