Prevention of common problems in municipal drainage pipes

The drainage system is one of the important facilities for the normal use of other engineering facilities in its service area, and it is very important to ensure the quality of its construction. Based on years of experience in construction technology, the author has conducted a comprehensive analysis of common problems in the construction quality of municipal drainage pipeline engineering. Now divide the most common quality problems into 4 areas, analyze their causes, and propose prevention and control measures for colleagues’ reference.

1 Pipeline position deviation or water accumulation 1.1 Causes: Measurement errors, construction sampling and accidental avoidance of original structures, resulting in positional deviation on the plane, and water accumulation or even falling slope on the facade.

2.2 Preventive measures:

(1) Measures to prevent diseases caused by measurement and construction mainly include:

①Re-test and protect the transfer piles in accordance with the construction survey specifications and regulations before construction.

②The construction lofting should be based on the hydrogeological conditions, in accordance with the embedding depth, design requirements and relevant regulations, and must be retested to verify that the error meets the requirements before delivery for construction.

③The construction should be carried out strictly according to the sample pile, and the groove and flat foundation should be well measured and accepted for the axis and longitudinal slope. To

(2) During the construction process, if a structure is encountered accidentally and must be avoided, connecting wells should be added at appropriate locations, and the connecting wells should be connected in a straight line. The rotation angle of the connecting wells should be greater than 135°.

2 The pipeline is leaking, and the closed water test is unqualified

2.1 Causes: Uneven sinking of the foundation, poor construction quality of pipes and their joints, improper sealing of the end of the closed water section, and poor construction quality of the well can all cause water leakage.

2.2 Prevention measures:

(1) Poor pipeline foundation conditions will result in uneven settlement of the pipeline and foundation, which generally results in local water accumulation. In severe cases, pipeline fractures or joint cracks may occur. The preventive measures are: ①Conscientiously construct according to the design requirements to ensure the strength and stability of the pipeline foundation. When the geological and hydrological conditions of the local foundation are poor, soil replacement and improvement treatment should be carried out to improve the bearing capacity of the bottom of the foundation trench. ②If the soil at the bottom of the trough is disturbed or soaked by water, the soft soil layer should be excavated first, and the over-excavated part should be sand or crushed.

Materials with good stability, such as stone, are backfilled and compacted. ③When excavating soil below the groundwater level, effective measures should be taken to prevent drainage and precipitation at the bottom of the trench to ensure that the dry trench is excavated. If necessary, a 20cm thick soil layer can be reserved at the bottom of the trench. Closed. (2) The quality of the pipe is poor, there are cracks or local concrete is loose, the impermeability is poor, and the capacity leaks. Therefore, it is required: ①The pipes used must have the quality department to provide the certificate and mechanical test report and other materials. ② The appearance quality of the pipe requires a smooth surface without loose bones and honeycomb hemp surface image, and the sound of a hard object tapping the pipe wall is crisp and pleasant. ③ Check again section by section before installation, and discard the ones that have been found or have quality doubts or use them after effective treatment.

(3) The quality of the filling and construction of the pipe joint is poor, and the pipe is damaged or the joint is cracked under the action of external force. Prevention measures: ①Select good quality interface fillers and organize the construction according to the test mix ratio and reasonable construction technology. ②The joints should be clean, and the cement filling joints should be pre-moistened. For oily ones, they should be pre-dried and then brushed with cold base oil, and then carefully constructed in accordance with the construction operation rules.

(4) The construction quality of the inspection well is poor, and the joints of the well wall and its connecting pipes are leaking. Preventive measures: ① The masonry mortar of the inspection well should be full and the joints should not be missed; clean and moisten the surface before wiping. Lightly harvest and maintain the slurry; when there is groundwater, the plastering and jointing should be completed in time with the masonry, and the inner plastering or jointing shall not be carried out after backfilling. ②The outer surface of the pipe connected to the inspection well should be moistened and evenly brushed with a layer of cement slurry, and then the inner and outer surfaces should be painted to prevent leakage.

(5) The closed water section is not tightly sealed and is often overlooked because it is in the well. If a brick wall is used for blockage, the following points should be paid attention to:

① Clean the inner wall of the pipe within about 0.5m of the pipe mouth before plugging it, paint the original cement paste, and moisten the bricks used for later use.

② The marking of the plugging mortar should not be less than M7.5, and it should have a good consistency.

③The mark of cement mortar used for jointing and plastering shall not be lower than M15. When the diameter of the pipe is large, only the external one-sided caulking or wiping should be done when the internal and external sides are small. The plastering surface should be constructed according to the waterproof 5-layer construction method.

④ When conditions permit, the inspection well can be sealed before the inspection well is built to ensure the quality.

⑤The preset drain hole should be at the inner bottom of the pipe for draining and inspection during testing.

(6) The closed water test is a comprehensive inspection of the pipeline construction and material quality, during which it is inevitable that there will be three or two failures. At this time, the leaks should be marked one by one, and the water in the pipe should be drained and dealt with carefully. For small gaps or pitted surface leakage, grout or waterproof coating can be used, and the more serious ones should be reworked. The grease interface can be surface treated with a blowtorch, which is generally effective, otherwise it will be dug out and refilled. In addition to replacing pipes and refilling the joints, serious leakage can also be handled by professional and technical personnel. Do the test after the treatment, and repeat the process until the closed water is qualified.

3 Deformation and sinking of inspection wells, poor quality of structural parts 3.1 Causes Deformation and sinking of inspection wells, poor quality of manhole covers and installation quality, and too much random installation of iron ladders, which affects appearance and quality of use.

3.2 Prevention and Control Measures (1) The base layer and cushion of the inspection well should be carefully inspected, and pipes should be broken to make the flow trough to prevent the well body from sinking.

(2) The masonry quality of the inspection well should be well controlled to prevent the well body from deforming.

(3) Check well cover and seat should be matched; when installing, the slurry should be full; the light and heavy model and the bottom of the surface are good to use, the iron climbing installation should control the position of the first step up and down, the deviation should not be too large, and the plane position should be accurate.

4 Subsidence of backfill

4.1 Causes of improper compaction equipment; poor filler quality and poor water content control affect the compaction effect and cause excessive settlement after construction.

4.2 Prevention and treatment measures

4.2.1 Preventive measures

① When the pipe groove is backfilled, suitable fillers and compaction (tamping) tools must be selected according to the backfilling position and construction conditions. For example, the pits and grooves of drainage facilities under the main roads in this area are backfilled with medium-coarse sand. Fill the tube groove from the thoracic cavity to the top of the tube 30cm, and then irrigate and vibrate until the relative density is ≥0.7. Practice has proved that the effect is very good.

②When the pipe groove is narrow, it can be filled with a mini-roller or manually or with a frog-type rammer. Different fillings and different filling thicknesses should choose different tamping tools to achieve the most economical compaction effect.

③The silt, tree roots, turf and decayed plants in the filler not only affect the compaction effect, but also shrink and rot in the soil to form holes. These materials should not be used as fillers to avoid sinking.

④ Control the water content of the filler to be greater than the optimal water content of about 2%; in case of groundwater or after rain, the water must be drained first, and then stratified and compacted with filling; avoid backfilling with water or water tamping construction.

4.2.2 Treatment measures Take corresponding measures according to the degree of settlement damage:

①Small settlements that do not affect other structures can be treated without treatment or only with surface treatment, such as partial filling on asphalt pavement to avoid accumulation of water.

②If the foundation of other structures is damaged, pumped cement slurry can be used for filling.

③If the structure is damaged, the poor filling materials should be excavated, replaced with materials with good stability, and restored to the damaged structure after compaction.

5 Concluding remarks The pipeline project is a concealed project. When it is completed, only inspection wells are available for people to inspect. Therefore, the construction quality of the inspection well often influences the evaluation of the overall project quality. Nevertheless, the author believes that excellence in drainage pipeline engineering must be established on the basis of excellence in main structural engineering. During the construction process, we must strive to overcome various common problems to ensure that the overall project construction quality is excellent, and then the inspection well construction quality should be better, so as to achieve the goal of excellence.

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