Application of Bentonite Waterproof Blanket in Landfill
1. Development of Bentonite Waterproof Blanket
1. Selection of raw materials
The main factors that determine the waterproof performance of bentonite waterproof blanket (hereinafter referred to as GCL) are: raw ore quality of bentonite (bentonite value, water content, permeability coefficient, etc.), material formula, material dosage per unit area and volume, special parts Treatment and the binding ability of the surrounding environment to the bentonite, etc.
The water swellability and water resistance of bentonite vary significantly with its type and place of origin. When choosing the raw materials of bentonite, we have conducted a lot of research and testing on the raw ore quality of bentonite at home and abroad, and compared some domestic bentonites with the United States. The differential heat and X-ray curvature of the clay used in the clay company's products were compared with those of the American Wyoming bentonite, and the control indicators such as the bentonite's bentonite value, permeability coefficient and expansion pressure were determined. After the raw materials of bentonite are determined, in order to improve the stability of bentonite after hydration and the hydrostatic pressure of the pit, and further improve the waterproof performance of the material, we also carried out various effects on the waterproof performance of different bentonite samples, and determined the best Types and parameters of admixtures.
2. Raw material selection of bentonite
The quality of bentonite is the most important factor affecting the waterproof performance of GCL. The commonly used test items to determine the quality of bentonite are chemical analysis. Cation exchange determination. Determination of clay mineral content, swelling value, swelling capacity, colloid value. water absorption. permeability coefficient, etc., but because some test methods are difficult to determine the properties of bentonite. In terms of quality, it has its limitations, so at present, the selection of bentonite at home and abroad is mostly based on the swelling value and permeability coefficient.
However, in our experimental research, we found that there is no complete correlation between the swelling value and the waterproof performance of the material. Some bentonites have a large swelling value, but the waterproofness, especially the resistance to hydrostatic pressure, is not high. Therefore, when selecting raw materials, we remove the In addition to measuring the swelling value and permeability coefficient, special attention is also paid to measuring the expansion force and expansion rate. In addition, different water quality has different effects on bentonite. For some application fields where leachate has a greater impact on bentonite hydration, bentonite must be pre-hydrated or modified, and anti-pollution bentonite must be used.
3. Structural anti-seepage of landfill and application of GCL
The construction of landfills is the primary method of disposal of municipal solid waste in most countries around the world. Currently, 95% of waste is disposed of in landfills in the United States, 90% in the United Kingdom, and 72% in Germany. The research and application of sanitary landfill in my country started relatively late. In 1991, the Ministry of Construction and the State Science and Technology Commission officially identified the sanitary landfill treatment technology as the preferred technology for waste treatment recently promoted in my country. This technology has developed rapidly in my country. It should be said that there are a lot of landfills in my country, but there are quite a few that really meet the standards of sanitary landfills. A few of the landfills that have been built still have problems such as landfill leachate contaminating water sources, soil sacs, and air pollution due to biogas overflow. This is actually closely related to the design of the anti-seepage layer, the selection of anti-seepage materials and the construction quality.
The main process of the landfill method is to set a seepage layer between the garbage heap and the surface. In order to protect the effective anti-seepage work, a complete anti-seepage structure generally also includes a protective layer. Leachate drainage layer, groundwater drainage layer. The anti-seepage material used in the anti-seepage layer mainly includes HDPE film. Non-woven geotextiles. Natural clay and bentonite waterproof materials, etc. HDPE film has good impermeability. It has the advantages of strong corrosion resistance and not easy aging, but poor resistance to uneven settlement and puncture resistance, so the single-layer HDPE film impermeable layer is generally prone to leakage problems, and the safety factor is low. In order to improve the reliability of the impermeable layer, composite The use of impermeable layers is also increasing. Before the appearance of GCL, the composite impermeable layer generally included a layer of geomembrane. 2 layers of non-woven fabric and 500~1000mm thick pressed clay layer. But since the appearance of GCL, GCL has a tendency to replace the pressed clay layer.
Compared with the pressed clay layer, GCL has the following advantages: First, the construction is simple, no heavy equipment is required, and the transportation volume of clay is greatly reduced in areas lacking high-quality clay; second, due to its thin thickness, it reduces the impact on landfill. The consumption of space; the third is that its ability to withstand uneven settlement is much more than that of compacted clay layers. The allowable tensile strain of general compacted clay is less than 1%, while the allowable tensile strain of GCL is as high as 8%; fourth, its ability to resist freeze fusion and dry-wet cycles is better. Generally, when the compacted clay is in a dry state for a long time, it will produce A large number of cracks increase its water permeability, and this process is irreversible, while GCL's water resistance is not affected after multiple drying-wetting and freeze-thaw cycles.
Therefore, at present, the GCL produced by us is not only widely used in the municipal and construction fields in Beijing, but also in Changshou and Wushan in the reservoir area of the Three Gorges City. Wuxi and other landfills have been applied; these three landfills use GCL with an area of 140,000 square meters.
Bentonite waterproof blanket (GCL) is a new type of geosynthetic material. After mixing the graded sodium bentonite particles and admixtures uniformly, through special technology and equipment, the high expansion sodium bentonite layer is made uniform by the strength of the fiber. Firm fixation and excellent anti-seepage performance. It can be stretched and partially lowered. Under the dry-wet and freeze-thaw cycles, it maintains extremely low water permeability, and also has the advantages of easy installation, low cost, and space saving. It has broad application prospects in various anti-seepage projects.