As a temporary building in water conservancy construction, the successful completion and safety guarantee of construction cofferdam often become the key to the success or failure of the whole project. The main function of cofferdam project is to intercept and retain water and create construction conditions for pumping station construction. Preventing water gushing and dam collapse are the keys to the success of cofferdam. (1) Cofferdam construction process: measuring and setting out → cleaning foundation → filling weir body → laying composite geomembrane facing water surface → soil bag protection. (2) According to the calculation results of the water surface line, the once-in-20-year water level of the pumping station is 120. 18m. Considering the superelevation of 0.5m, it is finally determined that the top elevation of cofferdam is 120.68m, and the maximum cofferdam height is 3.68m In order to ensure the dry land construction, soil cofferdam with trapezoidal section is adopted, and the slope ratio is 65,438+. Cofferdam is filled to 120.68m, leveled and rolled by bulldozer, and the compaction standard of cofferdam reaches over 90% according to the design requirements. In order to ensure the quality and stability of the cofferdam, a layer of composite geomembrane is laid on the water surface of the cofferdam, and then the cofferdam is protected by soil bags to prevent the river from washing the cofferdam. (3) Filling of weir body: 1) Before filling, the foundation within the weir body shall be cleaned and the basement shall be rolled, and the underwater part shall be dredged by excavator according to the actual situation. 2) The weir body is filled in layers by bulldozers, and the top width of the cofferdam is 3m. According to the design requirements, the compaction standard of cofferdam filling reaches more than 90%. 2. Foundation pit support Because the sluice foundation is composed of fine sand layer, medium sand layer and silty clay layer, considering the prevention of foundation pit collapse during excavation, steel sheet piles are used to surround the foundation pit in the cofferdam. 2. 1 firstly, according to the characteristics of the site where the project is located, combined with the characteristics and construction methods of steel sheet piles, steel sheet piles are selected. Larsen III steel sheet pile is selected, which has moderate width and good bending performance. Its main technical parameters are: W= 1600cm3, g=60kg/m, and according to geological data and operation, the length of steel sheet pile is 6m. 2.2 Single-pile driving method is used to drive the steel sheet piles one by one. A. First, the surveyors determine the axis of the steel sheet pile cofferdam, and guide piles can be set at regular intervals. The guide pile is directly made of steel sheet pile, and then the rope is used as the conductor, and the axis of the steel sheet pile is controlled by the conductor when piling. B, prepare the pile cap, and deliver the pile: the pile driver will lift the steel sheet pile and manually straighten it in place. 2.3 In principle, the pile can be pulled out after the culvert and exit retaining wall are completed. After the earthwork behind the wall is backfilled to half the height of the wall, the pile will be pulled out immediately and reused after the pile is repaired. First, clamp the pile head of the steel sheet pile with a pile driver and vibrate for 1 ~ 2 min, so that the soil around the steel sheet pile becomes loose and produces "liquefaction", which reduces the frictional resistance of the soil to the pile, and then slowly vibrate and pull it up. Pay attention to the load of pile driver when pulling out piles. When it is difficult or impossible to pull out the pile, stop pulling out the pile, vibrate for 1 ~ 2 min, then hammer down for 0.5 ~ 1.0m, and then vibrate again. So you can pull out the pile repeatedly. 3. Construction diversion and dewatering 3. 1 Brief description of hydrogeology The foundation of the drainage gate of the pumping station is composed of fine sand layer, medium sand layer and silty clay layer. The buried depth of groundwater level is114m ~15m, the aquifer is rich in water, the foundation sand layer is thick, and the Songhua River water is fully replenished. 3.2 The pumping station is Songbei Sewage and Rainwater Pumping Station, with the forced discharge flow of 65438+ 100m3/s and the diversion flow of 5m3/s (1). Considering the project investment, the project cost should be reduced as much as possible, and the existing actual drainage and peak drainage needs should be adopted, combined with the water storage capacity of the water collection tank, according to the drainage situation of the pumping station:1. 2) The existing daily displacement 10000 m3- 150000 m3 is discharged in two times, and the sewage pump with a flow rate of 5000 m3/h is used for one hour in the morning and one hour in the evening. (2) According to the above, the design basic displacement should be 30000m3 days. 1)5 sewage pumps, 22KW, flow rate 300m3/h, lift 15m, and 2 standby sewage pumps. 2) Discharged into Songhua River area by charging. 3) Ceramic tile 1.2M3 150 # mortar shall be used for joint filling at the outlet of water pipe. (3) After the construction starts, pumping test shall be carried out first to determine the displacement, and water pumps and pipelines shall be adjusted to meet the drainage needs. (4) The drainage pump should run day and night, and the power supply equipment should be double-line to prevent power failure or other accidents from affecting drainage. When necessary, the generator set shall meet the construction requirements. 24-hour patrol duty, equipped with electricians and mechanics. If it is found that the pump is stopped, it should be dealt with immediately, and the drainage should be resumed as soon as possible to prevent the overflow accident caused by the pump stop. 4. Earthwork construction 4. 1 Earthwork excavation This time, the earthwork excavation of the drainage gate foundation is 3000m3. The construction period is planned to be two days, with one excavation, and the daily excavation intensity is 1500m3. 2.0m3 excavator excavation, 20T dump truck transportation, respectively transported to the slag yard and storage yard. 4.2 earthwork backfilling earthwork backfilling construction shall meet the following requirements: before filling, the milk skin, dust, oil stains, etc. on the surface of the building shall be cleaned; Iron parts with exposed surfaces (such as formwork pins and bolts). ) should be cut off, if necessary, iron residual outcrop application cement mortar cover protection. 5. Concrete structures of concrete construction pumping station include dike-crossing culverts, reinforced concrete retaining walls, traffic bridge bent frames, plate beams and stilling basins at the exit section. Concrete pouring: (1) Commercial concrete is used for concrete supply. The mixture ratio issued by the testing unit entrusted by the commercial concrete mixing station with corresponding water conservancy qualification is used to guide the construction. The production capacity of commercial concrete mixing station can meet the concrete supply intensity required by engineering construction. When pouring concrete, the mixing station should have a special person on duty to be responsible for the supply and demand of concrete. After the commercial concrete arrives at the site, the experimenters will check the slump and workability of the concrete, make records, arrange and file them, and keep the corresponding number of concrete test blocks according to the construction specifications. (2) Before concrete pouring, it is necessary to clean up the sundries in the formwork, rinse with water gun, and wet the formwork, but there can be no water. At the construction joint, first spread 50- 100mm thick cement mortar with concrete strength. (3) The concrete shall be continuously poured in layers, and the method of circulating water shall be adopted to make the concrete rise evenly, with the height difference not exceeding 1.5m and the interval between layers ≯2h. (4) Vibrators should be "fast inserted and slow pulled", evenly distributed, with a spacing of about 400mm, step by step, and no vibration leakage is allowed. When necessary, assign special personnel to knock on the formwork to avoid causing holes in the concrete. When the upper concrete is vibrated, when the vibrator is inserted into the lower concrete not less than 50mm(5), when pouring concrete, check whether the position of formwork, steel bar and reserved hole moves at any time, and check whether the support system is firm. If problems are found, they should be repaired immediately and concrete construction should be suspended. (6) At the node intersections of walls, beams and columns, where steel bars are relatively dense, the concrete should be vibrated carefully to ensure that the concrete is dense, without holes and honeycomb pits, which will affect the concrete quality. (7) When pouring concrete, assign special personnel to take care of the steel bar, ensure the correct position of the steel bar, and clear the concrete lines on the steel bar in time. When pouring the flat plate, the plate should be laid in advance, and the steel bar should not be trampled at will. In particular, it is forbidden to trample and sink the upper negative bending moment slab reinforcement, and pay attention to the setting of the slab reinforcement protective layer. 6. Formwork production and installation 6. 1 Formwork installation (1) Formwork installation follows the principles of safety, convenience, quickness and beautiful concrete surface. According to different concrete parts, choose different template installation methods, and arrange the template installation sequence according to the overall construction progress and concrete pouring in layers and blocks. (2) Before formwork construction, organize drawing study, make technical disclosure, put forward installation scheme, and set out surveyors to ensure accurate position. Before template installation, remove template dirt and brush release agent. Template installation must ensure that the template joints are straight, neat and tight, and the positions of embedded parts and reserved holes are accurate without deviation. The reinforcement is safe and reliable, which is convenient for steel bar installation and concrete pouring and maintenance, and is conducive to speeding up the construction progress. Temporary bracing and reinforcement facilities shall be set up during formwork installation to prevent overturning. 6.2 Form removal (1) In order to protect the surface and avoid form removal at night, the time of form removal should be determined according to the weather, environment, structural type, characteristics and concrete strength: side formwork, side formwork and other non-bearing formwork can only be removed after the concrete strength reaches 3.5MPa; Bearing template, after the concrete strength meets the requirements of construction specifications, can be removed. (2) Dismantling shall be carried out from top to bottom, one by one; Dismantle the first branch, and dismantle the last branch first; Dismantle the non-bearing part first, and then dismantle the bearing part. During construction, dismantle the steel pipes and steel bars that are braced, loosen the bolts from top to bottom, take out the internal and external stare blankly, and take out the formwork. Pay attention to safety when ripping, and construction personnel shall not stand above or below ripping. Pay attention to the demolition skills, and don't pry or use excessive force to damage the formwork and structure; Formwork removed from a height should be put down slowly with a rope, and it is not allowed to be thrown around or damaged.
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