It is difficult to prevent leakage in sewage concrete pipeline construction, and closed water test is the main method to test whether it is successful or not. There are many reasons for pipeline leakage during construction, and each construction process may cause leakage, leading to the failure of closed water test. In this paper, preventive measures are put forward for the problems that need attention in each process.
First, the preparation before the tube. 1. Pipe joint inspection. Precast finished reinforced concrete pipes must meet the design requirements, and the inspection items include reinforced concrete strength, pipe size and appearance. The contents of visual inspection include: whether the pipe joint is damaged, cracked, exposed, peeled, exposed, deformed, partially collapsed, pitted, etc. 2. cut your hair. The specific method is as follows: chisel off the qualified concrete round pipe head section by section with a chopping axe. The width of each end should be 2 ~ 3 cm greater than the width of 1/2 tape, and the elevation of the pipe end should also be chiseled off together with the wall thickness. The quality requirement of chiseling is to chisel away the laitance layer on the surface of precast concrete and expose new stones and concrete stubble. When chiseling, do not use too much force to avoid damaging the pipe body or chiseling a gap. 3. Exhaust pipe. When laying pipes, the distance between two pipes is the joint, and the width of the joint is also one of the important factors affecting the leakage of pipes. According to the construction manual, the joint width is10 mm. If the joint passes through a narrow gap, it is difficult to form an effective adhesive tape, and the joint width is too wide, because the mortar strength is far less than the precast concrete strength of the circular tube, which will affect the overall strength and service life of the pipeline.
Second, the treatment of pipeline bottom interface. After laying the pipe, the pipe joint concrete can be poured. In order to prevent the concrete of the pipe socket from flowing into the pipe during vibrating, the flat foundation at the bottom of the pipe should be cleaned with water and the cement slurry should be brushed on the flat foundation with a brush.
Thirdly, pouring the concrete of the pipe seat. After the machining of the bottom of the joint is completed, the tube base template can be supported. The label of joint concrete is generally C 15. When pouring concrete, pay attention to embedding steel wire mesh. Steel wire mesh should not cling to the pipe wall to prevent water seepage, and should be 10mm away from the pipe wall.
Fourth, the interface is distorted. The twisting process is very important for the success of water stop. First of all, each interface should be cleaned repeatedly with a wire brush, and there should be no dirt, loose slag, oil pollution and other pollutants at the interface, which is beneficial to the combination of mortar and pipe joint. Then rinse with water, one is to clean the floating dust, and the other is to fully wet the interface. Subsequently, use a brush to brush the cement slurry at the joint, so that the mortar can be firmly bonded with the pipe wall. Twisting seam must be completed in several times, and finally, the cement mortar seal coat shall be filled to a place about 5mm away from the outer wall of the pipe, which shall be flat and wrinkle-free, and covered with wet sacks immediately after completion. Require moisture preservation, and often sprinkle water to keep sacks moist.
Fifth, wipe the tape. After the torsion joint curing time meets the requirements, we should first test the water and observe the quality of the torsion joint. If there is no water leakage, it can be treated with adhesive tape. Specific construction method: interface cleaning: ① firstly, repeatedly brush and clean the dirt such as laitance and loose slag on the surface of the pipe joint within the wiping range with a wire brush, and then clean it with a broom; (2) Sprinkling water for wetting: fully wet the interface with a brush dipped in water; (3) Brush the cement slurry: Dip the cement slurry with a brush and smear it on the adhesive tape. It is required to brush evenly, not too thick, and the width should be 3 ~ 5cm； larger than the width of the adhesive tape; (4) Binding: The mixing ratio of binding mortar is 1:2.5 cement mortar, and the mixing consistency should be moderate, and it should not be too thin and too soft. The mortar that is too thin and too soft is not easy to form during construction, and it is easy to dry and crack. The thickness of plastering belt is generally 25mm, and it shall be plastered to the design thickness twice. The first layer of mortar shall be compacted to make it firmly bonded with the pipe wall, and the plastering thickness shall be 10mm. After the initial setting of the bottom mortar, wrap the steel wire mesh reserved on both sides of the pipeline along the interface, straighten the steel wire at the end of the mesh, connect it firmly with the wire, press it into the mortar layer by hand, then screw it twice, and then wipe the second layer. Quality requirements of pipe belt: dense, smooth, equal width, centered (with seams), no cracking and no hollowing. ⑤ Maintenance: After plastering is completed, cover the mortar with plastic film immediately, and after initial setting, cover the mortar with wet sacks for moisture maintenance to ensure continuous moisture maintenance within 7d.
Six, inspection well masonry problems. In the closed water test, the bottom and wall of inspection well are prone to leakage. Cause of bottom hole leakage: Because the concrete flat foundation was not cleaned and washed before the bottom hole was bricked, there was mud or other impurities. When the closed water head reaches a certain height to generate water pressure, the pressure water leaks from the gap of silt or impurities; Causes of shaft wall leakage: the running water tank is not built with the inspection well, the masonry mortar is not full, the mortar of the ladder seat is not dense, the width of brick joint is unqualified, the joint is straight, the label of internal powder mortar is low, and the internal powder mortar can not reach the design thickness. In view of the above reasons, solve them one by one in masonry and prevent them in advance.
Seven, irrigation. When the joint between two wells is bonded, water should be injected immediately in order to check the bonding effect. When injecting water, the speed should not be too fast. When injecting water, it is required to repeatedly check each joint on both sides of the pipeline. Once the open water leakage is found, the water should be stopped immediately, and the water level in the pipe should be pumped out to make it lower than the leakage point, and it should be repaired immediately. After the repair, water injection inspection shall be continued until the pipeline is full. During irrigation, the water head should not be too high, and the upstream pipeline should be full. High water head and high water pressure will exert great pressure on joint adhesion. If the amount of water is less than that of the pipeline, it is easy to overheat or cool the empty pipe at the top of the pipeline, resulting in uneven thermal expansion and cold contraction; In order to ensure the quality of the pipeline and the best strength of the belt and torsion joint, the pipeline must be kept full of water until the cavity backfill is completed.
Eight, closed water test. After the acceptance of pipelines and inspection wells is qualified, and the end of the closed water section is sealed tightly and reaches a certain strength, the closed water method test can be carried out. The water level in the closed water test section should be 2m higher than the top of the upstream pipeline in the test section. If the design is less than 2m, the design height shall prevail. In the process of irrigation, check whether there is water leakage or serious water seepage in the belt wiping, plugging, pipe socket and inspection well at any time. In order to soak the inspection well, it should be filled with water for 24 hours before the test. During the test, the water level must reach the specified head height, and the infiltration test time should be no less than 30 minutes. The water seepage is calculated according to the drop value of water level in the well. The actual water seepage is less than the allowable value in the specification, and the inspection well and pipeline are watertight.
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