The main anti-seepage material in landfill sites, geomembrane, compared with geotextiles, ordinary soil and clay, has extremely low water permeability. It is a continuous polymer film that is basically impermeable. Moreover, it has many advantages such as easy construction, low cost and reliable performance. Therefore, it has been widely used in anti-seepage of landfill sites at home and abroad. Geomembranes can be classified into three major categories: geomembranes, reinforced geomembranes and composite geomembranes. Reinforced and composite geomembranes can significantly enhance the ability to resist puncture and water pressure, and are preferred in important projects.

To resist the invasion of various complex chemical elements in garbage, it is generally required that its raw material be high-density polyethylene (HDPE). They are used as the main anti-seepage layer of the liquid collection layer in the bottom liner system, the secondary anti-seepage layer of the liquid detection layer, and the anti-seepage layer of the cover. If the main and secondary double-layer geomembranes are used in the garbage pit, their materials and thicknesses should be the same. When the thickness of the landfill is large, significant pressure will be generated. It is necessary to pay attention to the protection of the geomembrane. Using geotextile as a protective layer is quite effective.

The base drainage generally adopts a uniformly graded granular drainage layer, but geocomposite drainage materials (composite drainage nets) can also be used. That is, geocomposite drainage nets are set up at a certain position below the surface layer and their two ends are connected to the roadside drainage. There are mainly three forms:

(1) It is set under the base granular material

Shorten the effective drainage path and accelerate the drainage speed. Since the drainage resistance of the geocomposite drainage net is much smaller than that of the granular material base layer, the time required from the granular material base layer to the geocomposite drainage net is the controlling factor of the drainage time. In this way, the effective drainage path is equal to the thickness of the base layer. However, when draining the base layer of pure granular materials, the effective drainage path is equal to the width of the road. In contrast, the effective drainage path is significantly shortened.

② Prevent fine-grained soil from the roadbed from entering the base layer (i.e., the isolation effect). The isolation effect and drainage effect together enhance the stability and bearing capacity of the foundation, thereby allowing for the paving of roads on soft soil foundations (i.e., CBR < 3).

③ Improve the drainage conditions to enable the soft soil foundation to gradually consolidate.

④ To a certain extent, it can restrict the horizontal movement of the base granular materials, achieving a certain effect similar to reinforcement.

(2) Under the asphalt or cement concrete surface layer (PCC), as time goes by, cracks may appear on the road surface, allowing water to seep through these cracks into the base and subgrade. In such cases, the geosynthetic drainage net will drain away this part of the water to prevent it from seeping in. To prevent seepage, sometimes a layer of geomembrane is added at the bottom of the geocomposite drainage material.

(3) It can be set in the roadbed to replace the traditional horizontal drainage layer of gravel and sand. Combined with vertical drainage belts or gravel piles, it can quickly drain the consolidated drainage of the foundation soil and the water seeping from the pavement into the roadbed. It isolates the upper layer of filler and the foundation soil layer to prevent the mixed pollution of soft soil and filler in the foundation. Meanwhile, it has a certain reinforcing effect on the foundation. :

In the frozen areas of the north, it can also alleviate the impact of frost heaving. Its advantages are manifested as follows: as a capillary water barrier, it can lower the groundwater level, and the backfill soil that is prone to frost heaving can be directly filled on the surface of the geosynthetic drainage network. Limit the development of ice crystals in the foundation soil and reduce the pavement damage caused by frost heaving; In cold regions, when ice melts in spring, there is no need to limit traffic loads.

Geocomposite drainage materials must have high compressive strength and sufficient water conductivity. When laid under the base layer, the compressive strength is required to be approximately 239-478kpa. When directly laid under the asphalt surface layer, the compressive strength is required to be greater than 1435kpa. Although most geocomposite drainage materials have sufficient strength, they often fail to meet the drainage requirements under pressure due to significant deformation. This should be given due attention in the design and material selection.

Construction rules for the anti-seepage membrane of the farm sewage treatment plant: During transportation, physical damage to the anti-seepage membrane should be prevented. Impermeable membranes that are prone to severe wear and tear cannot be used in engineering. At the construction site, anti-seepage membranes should be stacked in a flat and water-free area. The stacking height should not exceed the height of five rolls, and the roll identification sheet should be visible. The anti-seepage membrane is covered with opaque materials to prevent ultraviolet aging. During the storage process, the integrity of the labels and the data should be maintained.

The construction site must clean the base surface as per the design requirements, which is the key to ensuring the anti-seepage effect. In particular, sharp stones, tree roots and debris must be completely removed. The base surface is not allowed to have any local unevenness. The cleaned base surface must be tamped down with a tamping hammer or a plate to make it dense and flat. The soil material of the 10cm thick protective layer on the anti-seepage membrane must be sieved. Particles larger than 6 millimeters in size are not allowed; otherwise, the impermeable membrane is prone to puncture. When laying geomembranes, they must be laid from top to bottom. The membranes should be flat and tight between each other and between the membrane and the base surface, but not stretched too tightly. Generally, they should be slightly loose, but there should be no air bubbles at the bottom of the membrane. After the protective layer is laid, it is prone to be blown away by the wind before the protective layer is laid. Therefore, the area of the film laid at one time should not be too large, and the protective layer soil material should be covered when laying the film. When backfilling the protective layer and the block stone protective surface, they must be gently lowered to avoid damaging the anti-seepage membrane. The seams of anti-seepage membranes can be made by hot bonding, gluing and lapping. After the anti-seepage membrane is laid, try to minimize walking on the membrane surface and moving tools.

Users who have applied geosynthetic materials such as geomembranes may be aware that they possess excellent anti-corrosion performance, electrical performance, moisture-proof performance, anti-seepage performance, and high tensile strength. It is precisely because of these outstanding properties that the production of geomembranes can currently be applied to wire and cable, engineering anti-seepage, aquaculture anti-seepage, and oil tank anti-seepage. Geomembrane is used in fields such as basement anti-seepage, artificial lake anti-seepage, landfill anti-seepage, and solid waste landfill anti-seepage.

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