一、 Methods and requirements for soil foundation cleaning and rolling in the landfill area.
1、 Methods and requirements for soil foundation cleaning and rolling in the landfill area
1. The bottom of the landfill area shall be leveled with a grader, leveled with a level gauge, cleaned and leveled manually, and compacted tightly. Weeds, stones, sundries and surface virtual soil in the site shall be completely removed. If deep roots of plants are found at the cleaned site bottom, they shall be pulled out manually.
2. The filling soil shall be silty clay as much as possible, and compacted layer by layer, with the compaction density not less than 0.95. Particle size of backfill. The uniformity and chemical compatibility shall be approved by the supervising engineer. The calcium content is too high to be used as backfill.
3. For the rock area with large edges and corners, the rock area shall be leveled before the geomembrane is laid, and then it shall be troweled with cement mortar.
4. At the bottom of the groove, hammer the small square wood (the small square wood is 5cm long and 2cm long × 2 ㎝ Square), the spacing of small square timbers is 5m, and the plum blossom type. The design elevation of the trough bottom + 20 ㎝ elevation line is marked on the small square timbers with a level gauge. The foreman personally checks the elevation of the trough bottom. The high place is leveled manually, and the low place is padded to the design elevation after the planting soil of the trench is screened. After the pressure is discharged by a 12t roller, the sampling test shall meet the design requirements. The foundation surface must be flat, free of cracks, obvious sharp projections and depressions. The flatness shall change gently within the allowable range, with uniform gradient and consistent slope direction, and meet the requirements of the drawings. For the slope of the foundation pit, according to the plane size of the drawing, nail small square wood at the lower end and upper end of the pit bottom to hang a line, hang a line every 10-15m, and level the slope according to the line. The internal and external corners on the foundation surface shall have a smooth transition radius of less than 10cm, and the slope surface shall be free of bricks, stones, granular hard impurities, branches, weeds, etc. the next process can be carried out after the entire foundation pit surface passes the acceptance.
2、 Construction requirements for laying of geomembrane and non-woven fabric
1. Before the laying of geomembrane, the supervision engineer shall be asked to comprehensively confirm the site conditions to ensure that the foundation surface of the landfill area is flat, free of unevenness, cracks, sharp particles, hard sundries, etc., and free of various foreign matters that may damage the geomembrane. The quality of the impervious material (whether there are bubbles, holes, wrinkles, damages, etc. on the surface of the known performance indicators) shall be strictly checked and the laying can be carried out after confirmation.
2. The sampling for acceptance inspection of geomembrane shall be based on the continuous production of products with the same brand of raw materials, the same formula, the same specification and the same process. The inspection items shall follow the performance content of bentonite blanket and HDPE geomembrane. The supporting granular bentonite powder shall be sodium based bentonite recommended by the manufacturer and the same as that in the bentonite blanket. Check whether there is damage, fracture and other phenomena during transportation. The product identification shall be verified.
3. Each roll of material shall be numbered and laid in sequence. The geomembrane shall be numbered and filed by the supervision engineer for inspection.
4. The geomembrane materials for on-site construction shall not be exposed for a long time and kept away from the fire source. The storage of the bentonite waterproof blanket and the supporting bentonite powder must be covered with plastic cloth or impervious film. The laid bentonite waterproof blanket shall not be left uncovered overnight to avoid premature hydration.
5. During the laying process, the staff shall not wear shoes that damage the bentonite waterproof blanket and geomembrane, and shall not smoke at the laying site or carry out other activities that can damage the bentonite waterproof blanket and geomembrane.
6. Before laying the bentonite blanket, attention shall be paid to the positive and negative directions of laying. During laying, the dragging of the bentonite blanket on the foundation shall be minimized to avoid damage to the bentonite blanket. If necessary, a layer of temporary geotextile can be placed on the ground to reduce friction.
7. The laid anti-seepage materials shall be pressed and placed in time to prevent them from being blown away by the wind.
8. The outdoor construction of geomembrane shall be carried out in the weather where the temperature is above 5 ℃, the wind force is below level 4, and there is no rain or snow.
9. No vehicle is allowed to drive directly on the bentonite blanket, HDPE geomembrane and non-woven fabric.
10. In order to avoid shrinkage and wrinkle of materials or stress of materials due to temperature change, the HDPE geomembrane shall be welded in time after the approval of the supervision engineer, and the protective materials shall be laid after passing the inspection.
11. During the welding construction of geomembrane, the supervision engineer shall be invited to inspect the operation procedure, laying and welding quality in time. If any quality problem is found, it shall be repaired in time.
12. The anchor ditch of the geomembrane intermediate platform and the anchor ditch at the slope top shall be free of tree roots, stones and large particles, and shall be leveled and compacted.
13. The longitudinal arched length of the bentonite blanket shall not be less than 150mm. If the non-woven fabric at the end of the bentonite blanket is not cut in a groove shape, it is necessary to use bentonite to reinforce the arched area. The transverse end laps of the bentonite blanket shall be at least 600mm long. All transverse end laps of knitted stiffeners need to be reinforced with bentonite. The amount of reinforced bentonite shall not be less than 0.4kg/m.
14. When the bentonite blanket is damaged, a piece can be cut on the new bentonite blanket for patching. The distance between the four sides of the patch and the damaged place shall not be less than 300mm. Before laying the “patch”, some granular bentonite or bentonite slurry shall be sprinkled around the damaged area. If necessary, some adhesives can be used to prevent the “patch” from shifting.
15. Requirements for welding position and welding technology of geomembrane:
(1) When the geomembrane welding on the slope is arranged, the lap joint shall be parallel to the direction of the slope, and the lateral lap joint of the slope shall be more than 1.0m away from the side line of the slope bottom.
(2) The formal welding shall not be started until the sample welded by the welding equipment has passed the test welding inspection or confirmed by the supervising engineer.
(3) Dust, dirt and other foreign matters on the surface of geomembrane must be cleaned before welding.
(4) The overlap of two welded geomembranes shall not be less than 10cm.
(5) When the temperature is lower than 5 ℃ or higher than 40 ℃, the construction unit shall provide a written description of the same welding quality within the specified temperature range and submit it to the supervision engineer for confirmation before construction.
(6) The welding form of geomembrane adopts double weld overlap, and extrusion welding is used in repairing (such as repairing holes) where the fusion welding equipment cannot reach.
(7) The joint strength of the geomembrane weld shall be greater than that of the parent material.
16. The construction site shall be equipped with sufficient welding equipment to ensure continuous welding construction.
17. The construction site shall be equipped with a testing laboratory and necessary testing equipment, and non-destructive tests (such as air inflation and vacuum tests) and destructive tests (such as shear stripping tests) shall be carried out on the HDPE geomembrane welds.
18. The on-site inspection of geomembrane welding is completed. All air filled raincoat piercers shall be immediately plugged with the extrusion weld method.
19. Repair welding shall be carried out in time for the joints with faulty welding and missing welding, and vacuum inspection shall be carried out for the repaired parts.
20. The construction unit must have a complete construction organization plan, reasonably arrange materials according to the size of the construction site, GCL and HDPE geomembrane, and reduce the loss of geomembrane.
21. GCL and HDPE geomembrane suppliers shall guide the construction or installation of anti-seepage system.
三、 Construction requirements for clay protective impervious layer
1. Before construction, the clay shall be carefully selected, and the debris such as stones, tree roots, branches, glass slag, reinforcement heads and other sharp objects in the clay shall be completely removed to prevent damage to HDPE geomembrane and non-woven geotextile.
2. For dry and hard clay blocks, special personnel shall be assigned to remove them to prevent the damage of high-strength, high elongation and environment resistant rough surface geomembrane and non-woven geotextile during compaction or rolling with light roller.
3. The water content of clay shall be strictly controlled. After mobilization, professional and technical personnel shall be invited to test the optimum water content of clay on site to ensure that the density of compaction meets the design requirements. The clay with large water content shall be dried. The clay with water content less than the optimum water content shall be watered. The clay shall be transported to the upper and lower slopes by the dump truck, and then backfilled by the trolley and manual.
4. The construction direction is along the construction direction of non-woven geotextile, and the earth is mainly transported by manual truck, and the springboard or steel formwork is laid on the earth, and the earth is transported by trolley. Spread along the construction direction to prevent damage to the impervious layer and non-woven geotextile.
5. The clay protective layer is paved and rolled in two layers. The first layer is 20cm thick and the compaction direction is perpendicular to the filling direction. The compaction thickness of the second layer is 10cm. In order to ensure the compactness of more than 80% as required by the design, the loose paving coefficient of clay shall be determined by field test. Manual tamping shall be adopted to tamp in the vertical paving direction, and the compactness shall meet the design requirements.
6. The first layer shall be compacted by hand-held vibratory rammers, and 4-6 hand-held vibratory rammers shall be used for step compaction. When the design requirements are met, the second layer shall be backfilled and compacted after being accepted by the supervising engineer. The upper layer shall be compacted by 1-1.5t small roller or hand-held vibratory rammer to meet the design requirements. After the self inspection is qualified, it shall be reported to the supervision engineer for inspection, and the next process shall be carried out after it is qualified.
Laying technology of gravel layer and gravel layer
1. The gravel layer is used for diversion, so we strictly control the quality of gravel during construction, mainly controlling the gravel diameter (2-10mm) and ensuring that there is no sand, soil and other sundries.
2. The gravel layer shall be backfilled with a thickness of 10cm, and the gravel shall be laid manually. The laying direction shall be along the construction direction, without compaction and rolling.
3. A groove shall be reserved at the diversion pipe, and the gravel shall be transported by a trolley with a springboard and leveled manually.
4. After the first layer of sand and gravel is laid, the second layer of 16-32mm and 20cm thick gravel diversion layer shall be laid and leveled manually.
5. A stepped groove is set at the diversion pipe.
四、 Construction method of leachate pipe, collection ditch and inspection well
1. The leachate pipe of the project is HDPE φ 250、 φ 350 plastic pipes are ordered from professional manufacturers.
2. The construction sequence is: acceptance of anti-seepage membrane protective layer → cleaning of construction surface → installation → inspection → acceptance.
3. The construction process is as follows: the primary and secondary leachate pipes of the landfill site shall be set out according to the plan position, and the protective layer soil at the plane position of the pipes shall be cleaned according to the setting out, and the impervious membrane shall not be damaged. If there is any damage, it must be repaired in time. The graded gravel and coarse sand protective layer must be evenly laid and compacted, and its thickness and slope meet the design requirements. The backfill at the trench must be compacted in layers, and the backfill density shall be more than 90%.
4. Main construction quality measures
1) The pipeline setting out shall be based on the location of the landfill pit, the center line of the ring road, the planned pile position and the coordinate value before construction.
2) Before construction, the elevation of the bottom of the landfill pit must be retested, and the impervious layer and the cushion soil above the impervious layer must be checked to see if they meet the requirements. Construction can be carried out after there is no error.
3) The construction operation of PE seepage pipe network must meet the design requirements. Before construction, the previous project must be accepted. The installation and construction of the pipe network can be carried out only after it is qualified, and the quality acceptance shall be carried out according to the project sequence during the construction process.
4) The materials used in the HDPE pipe must meet the design requirements and have quality certificates. HDPE pipes must be manufactured with the same raw materials and formulas as HDPE anti-seepage film. They must be inspected before use. The quality is qualified and there are certificates. Unqualified or non-conforming pipes cannot be used.
5) The foundation must meet the design requirements. Before the construction of the anti-seepage element at the root of the membrane pipe, the supervisor must test the water and observe that there is no leakage for 24h before the construction.
6) The installation shall be carried out in the rain free weather between 5 and 40 ℃. The installation and construction of HDPE pipe network shall be determined according to the design requirements of the drawings. After the pipe foundation is completed, the installation and construction sequence of pipe network shall be from low to high. After all the installation is completed and qualified, all the trusteeship carts and wooden bricks under the pipe belly shall be removed to ensure that the whole pipe network is implemented on the pipe foundation. The next process can be carried out only after the re inspection meets the design requirements.
7) The pipe orifice shall be perpendicular to the axis and the length of the pipe shall be 10mm longer than the design length.
8) The installation of PE pipes must meet the design requirements. The alignment deviation of the pipe orifice shall not be greater than 15% of the pipe wall thickness. Otherwise, it must be disconnected and re welded. Acceptance can be carried out only after the re welding is qualified.
9) The tensile breaking force of the pipe shall not be less than 70% of the tensile breaking force of the pipe. The weld strength shall only be conducted in the laboratory before installation, and destructive test shall not be conducted on the welded weld.
10) Personnel entering the site shall not step over the welded pipes. When entering the next process after installation, they shall not damage the pipes. If there is any damage, it shall be repaired in time.