The development of the mining industry brings not only a large amount of ore but also many tailings problems to be solved. Yet, tailings stored in tailings ponds often contain a large number of metals, heavy metals, and mineral processing residues. Once environmental pollution occurs, the consequences will be very serious. Thus, anti-seepage measures are usually taken for tailings ponds. The anti-seepage material selected is anti-seepage Geomembrane.
A. Construction plan of geomembrane for tailings pond
1. Preparation before laying geomembrane
(1) Flatten the ground on-site to make the surface flat and compact, and there are no bumps on the ground surface, no hard objects such as large stones, iron wires, etc., to prevent the impermeable membrane from being punctured;
(2) 40*40 anchoring trenches are dug around the landfill to prepare for the anchorage of the anti-seepage membrane on both sides of the landfill.
2. Laying of geomembrane
(1) Flatten the geomembrane membrane to be laid in the open space, and cut it into the required shape according to the predetermined plan;
(2) To avoid man-made damage to film laying, it should be smooth and compact, cut wrinkles, choose the laying direction, reduce the stress on the joints as much as possible, arrange the position of each piece of material, and strive to make the joints better. less is better;
(3) Lay the film on the flat ground, calculate and select the film laying method of the matter, reduce the number of welding seams and save materials as the standard. In the film laying process, artificial damage should be avoided, and the welding seams of adjacent geomembranes should be dislocated according to the “D” shape laying, besides, pay attention to reserve the amount of deformation and expansion of the excavated membrane when laying the film, generally reserve the amount of 1%-4%, which is determined according to the actual situation of the specific site to prevent the anti-seepage membrane from being stressed when the foundation is deformed torn;
(4) All exposed geomembranes must be pressed with sandbags or other heavy objects immediately to prevent the geomembrane from being blown up by the wind or pulled out of the surrounding anchoring ditch.
3. Welding of geomembrane
The climatic conditions required for geomembrane welding and stitching are: the atmospheric temperature is between 4-40 °C; dry conditions, especially without precipitation or other excessive moisture such as fog or dew; the wind speed is not greater than 4 per hour.
(1) Hot melt welding
Geomembrane membrane blocks must overlap by 15cm before welding, and the membrane blocks must be adjusted so that the seam minimizes the possibility of wrinkles and “fish mouths”; before welding seams, the seam area must be cleaned before seaming to ensure clean and free Water, dust, debris or any debris.
(2) Extrusion welding
The welding seam of the geomembrane membrane block should overlap by 7.5cm, and the seam area must be cleaned before sewing to ensure that the area is clean and free from water, dust, garbage or any debris; the hot air device can only be used for the heating bonding of the geomembrane module, Care should be taken not to damage the geomembrane, and polishing should not damage the geomembrane; the electrodes must be kept clean and dry.
4. Geomembrane welding details
Use a soft ladder on the slope of the tailings pond, and use a hot-melt welding machine to weld up and down the slope. When welding to the platform, lift the equipment. For the slope of 1:3 to 1:2, now The geomembrane in the recessed step can be lifted to the same line as the welding track that the welding machine took before. Now, the geomembrane at the step can be welded, and there will be no repair. When the whole length of welding is completed in this way, go back and use a sandbag to press the geomembrane into the anchoring groove on the platform (the membrane at the bottom of the slope is not fixed), and then use pebbles to anchor the membrane in the anchoring groove on the platform.
(1) When welding from top to bottom, stop welding when it reaches the platform.
(2) When the welding seam outside the platform is finished, the geomembrane is pressed into the anchoring groove when the platform is out, and the seam is exposed;
(3) Blow and connect the overlapping parts of the two geomembranes with a hot air gun;
(4) Use a grinder and sandpaper to roughen (above 1.5mm), and the chamfering angle is 45° (when the extrusion welding machine is welded because there is an oxide layer on the surface of the membrane, the geomembrane to be welded must be roughened, and the thickness after chamfering It can be ground about 0.5mm, and there is very small unevenness on the film, which can increase the contact area of
B. Precautions for construction of geomembrane in the tailings pond
1. Precautions for construction workers
(1) Before the geomembrane is laid, it should be ensured that the laying surface meets the design requirements and the quality and safety requirements;
(2) The material and quality of the geomembrane and electrode will meet the design requirements and the provisions of relevant standards;
(3) Persons unrelated to laying will not enter the construction site;
(4) All personnel entering the construction site of the geomembrane will wear an access card and shoes that do not damage the geomembrane, and no one will smoke when entering the site;
(5) When handling the geomembrane, all tools must be handled with care, and must not be thrown or replayed. It is forbidden for hot tools to come into contact with the geomembrane.
(6) After the construction of the geomembrane, attention must be paid to the protection of the finished product;
(7) Geomembrane will not be pulled, lifted, or rolled up using any equipment that may cause mechanical damage to the material during loading, unloading, and handling.
2. Welding precautions
During the welding process of the geomembrane, to prevent the membrane from being displaced by the strong wind after laying, the welding and pressing are adopted to advance in turn while laying. Before welding, wipe the reserved lap welding surface of the geomembrane clean; the rollers of the welding film machine should be wiped clean, and the equipment can be adjusted after the sample is welded before welding. When welding, always keep the welding machine moving at a constant speed. After the weld is completely cooled, the weld inspection test is carried out until the weld meets the requirements.
3. Defect and damage repair
During the geomembrane laying process, any defective or damaged geomembrane and non-destructive test should be repaired, so as not to affect the anti-seepage effect.
(1) Small holes should be repaired by extrusion welding, if the hole is larger than 6mm, it should be patched;
(2) The peeling application patch repair, if the peeling has a very sharp end on the slope, it must be cut into a circle before applying the patch;
(3) The surface of the geomembrane that needs to be patched should be repaired, polished, and cleaned in advance;
(4) The folded geomembrane should be re-laid, and the patched welding position should be parallel to the slope instead of crossing;
(5) The patch should be composed of the same geomembrane and cut into a round or oval shape, the size of which should exceed the edge of the defect by at least 15cm;
(6) All patches should have the same thickness as the original geomembrane, almost all patches should have the top edge flattened with a sander before being placed on the geomembrane, and all surfaces should be kept clean and dry during repair;
(7) Non-destructive testing should be performed for each repair location and recorded.
4. Fixing and protection of geomembrane
During the construction of the geomembrane of the tailings pond, the surrounding areas will be anchored, and the edge sealing will be anchored by anchoring trenches. The anchoring trench will be ditched 40cm away from the construction plane, with a trench width of 40cm and a trench depth of 40cm, and the geomembrane will be pulled into the trench to form a U-shape. , fix the trench with sandbags or concrete structures. At the same time, to strengthen the protection of the geomembrane and make its service life longer, the following measures are generally taken protection:
(1) Lay a layer of geotextile on the paved membrane for protection, and then lay a layer of sand or soil on the geotextile for secondary protection; lay a layer of fine soil on the paved membrane or use a wire mesh to make it. A layer of concrete, plus landscaping.
(2) Geomembrane can be constructed in a humid environment, but immersion in water should be avoided.
(3) If there is moisture on the ground, drainage measures should be taken before laying, so to prevent the geomembrane from being unable to be welded after sticking to water.
(4) When loading and unloading, according to the principle of handling with care, throwing, dragging, rolling, and damage are prohibited.
(5) When the geomembrane is not in use, it should be stored in a cool and dry place, and it is forbidden to expose it to the sun and rain.