Case study of anti-seepage engineering for sewage treatment tanks

　　Due to the production of a large amount of wastewater that is harmful to the environment in the chemical industry, the anti-seepage performance of sewage tanks has become an important indicator. Due to its excellent plasticity and chemical stability, HDPE anti-seepage geomembrane can resist the corrosion of over 80 strong acidic and alkaline chemical media such as various acids, alkalis, salts, and oils. Therefore, it has been widely used in fields such as chemical engineering and sewage treatment.

　　Construction procedures for HDPE anti-seepage geomembrane:

　　Surface requirements for anti-seepage and chemical anti-corrosion engineering of sewage tanks

　　1. Most chemical sewage tanks are of mixed territorial structure, with a relatively flat surface. It is only necessary to pay attention to cleaning debris such as debris, stones, steel reinforcement heads, and glass chips inside the tank.

　　2. The internal and external corners on the base surface should have a smooth transition, and the root of the column should be made into an arc shape.

　　3. After the civil engineering, supervision, owner, and construction party sign and approve the acceptance, the construction of geomembrane can be carried out

　　Laying of HDPE anti-seepage geomembrane

　　Laying HDPE anti-seepage film is a crucial process in the entire anti-seepage system.

　　Before laying the membrane, conduct an open-package inspection of the appearance quality of the anti-seepage membrane, record and repair any mechanical damage, production trauma, holes, folds, and other defects that have been discovered.

　　Before cutting the anti-seepage membrane, the relevant dimensions are measured, and then cut according to the actual situation. During the laying of the membrane, the overlapping width of the joint between the membrane and the membrane should not be less than 100mm, so that the joint arrangement direction is parallel to the foot line of the large slope, that is, along the slope direction.

　　When laying the impermeable film, efforts should be made to minimize the number of welds and, while ensuring quality, try to save raw materials as much as possible. It is also easy to ensure quality.

　　Usually, in corners and deformed areas, the joint length should be minimized as much as possible. Except for special requirements, welding seams should be avoided as much as possible within a range of 1.5 meters from the top slope or stress concentration area on slopes with a slope greater than 1:6.

　　During the laying of the anti-seepage membrane, artificial wrinkles should be avoided. When the temperature is low, it should be tightened and flattened as much as possible.

　　After the completion of the anti-seepage membrane laying, it is necessary to minimize walking and moving tools on the membrane surface. Any objects that can cause harm to the HDPE membrane should not be placed or carried on the membrane to avoid accidental damage to the membrane.

　　Welding of HDPE anti-seepage geomembrane

　　The welding of the anti-seepage membrane is carried out using a wedge welding machine and a dual track hot melt welding. For areas that cannot be welded by a wedge welding machine, an extrusion hot melt welding machine should be used, accompanied by welding rods of the same quality as the raw materials, to form a single weld seam for overlay welding.

　　1. The welding process of a hot wedge welding machine is divided into: adjusting pressure, setting temperature, setting speed, inspecting weld overlap, installing film into the machine, and starting the motor.

　　2. There should be no oil or dust at the joints, and there should be no debris such as sediment, condensation, or moisture on the overlapping surface of the anti-seepage membrane. When there are debris, they must be cleaned before welding.

　　3. At the beginning of each day's welding, a 0.9mm trial weld should usually be conducted on site first × A 0.3mm sample with a lap width of no less than 10cm shall be subjected to peel and shear tests on site. Once the sample is qualified, it can be welded using the adjusted speed, pressure, and temperature at that time. During the welding process of the hot wedge welding machine, it is necessary to pay attention to the operation of the welding machine at all times, and adjust the speed and temperature according to the actual situation on site.

　　4. The weld seam should be neat, beautiful, and free from slipping or jumping.

　　5. When the length of the geomembrane is not enough, it is necessary to splice in the long direction. The transverse weld should be welded first, and then the longitudinal weld. The transverse weld should be in a T-shaped shape with a distance of more than 50cm and should not cross.

　　6. When welding the film, it is not allowed to press out dead folds. When laying HDPE geomembrane, the expansion and contraction deformation caused by temperature changes should be reserved according to the local temperature change amplitude and the performance requirements of HDPE geomembrane.

　　7. Welding cannot be carried out during rainy periods or when there is moisture, dew, or heavy sand at the joints, unless protective measures are taken.

　　When the temperature is below 5 ℃, construction should not be carried out according to the requirements of the specifications. If construction is necessary, the welding machine should be preheated before welding.

　　When welding HDPE anti-seepage geomembrane, a generator with good voltage stability should be used for power supply. In special circumstances, when using local electricity, a voltage stabilizer must be used.