High density polyethylene (HDPE) pipeline

1. Construction process: Construction preparation → measurement and laying out → trench excavation → foundation treatment → installation of double wall corrugated pipeline → interface treatment → inspection well construction → closed water test → backfilling and compaction → inspection and acceptance. 2、 Construction plan and technical measures 1. Construction preparation (1) Material inspection: Before the pipes enter the site, the specifications and dimensions should be checked, and the appearance should be inspected. Cracks and deformed pipes should be removed, and samples should be taken for performance tests such as ring stiffness and tensile strength. The rubber ring should match the pipe material, have good elasticity and no aging or cracking. (2) The site shall be leveled and obstacles in the construction area shall be removed. The excavation slope and support scheme of the trench shall be determined based on the geological survey report. Soft soil layers shall be replaced and filled in advance. (3) Organize construction personnel to study design drawings and specifications for technical disclosure, clarify technical parameters such as pipeline slope and interface form, and develop special measures for special geological conditions. Before construction, the project technical leader shall provide written technical instructions to the construction workers. (4) Equipment debugging checks the performance of excavators, cranes, compactors, and other equipment, equipped with measuring tools such as total stations and level gauges, and calibrated. 2. Surveying and laying out (1) Positioning control

Using a total station combined with GPS to locate the centerline of the pipeline and the position of the inspection well, temporary leveling points are set with a spacing of no more than 100m. After introducing elevation control points, closed measurement is carried out with slope error controlled within ± 0.5%.
(2) Mark the edge of the trench with white ash for protection, with a pile distance of 5-10m. Use red flags to mark the detection results of underground pipelines, and manually confirm the trench in complex areas. 3. Trench excavation (1): After excavating the trench layer by layer with machinery to a height of 200-300mm above the design elevation, manual cleaning of the trench should be used to avoid disturbing the undisturbed soil. The width of the groove bottom is controlled by adding 300-600mm to the outer diameter of the pipe. The slope gradient of sandy or loose soil layers is 1:1.5, and the slope gradient of clay can be appropriately steepened to 1:0.75. (2) A 300mm × 300mm drainage ditch is set up along both sides of the trench for drainage and precipitation. A collection well is set up every 50m. When the groundwater level is higher than the bottom of the trench, the well point is used for drainage to 0.5m below the bottom of the trench. (3) When the depth of the safety protection trench exceeds 1.5m, a protective fence is set up, warning lights are hung at night, and the excavation length is shortened during the rainy season and the slope is covered to prevent erosion. 4. Foundation treatment (1) Cushion layer construction: Generally, a 100mm thick medium coarse sand cushion layer is laid on the soil foundation, and a 200mm thick graded sand and gravel layer is used on the soft soil foundation. After paving, a flat vibrator is used to compact it with a compaction degree of ≥ 95%. (2) The interface groove is reserved at the socket part with a length of 0.4-0.6m and a depth of 0.05-0.1m, with a width of

1.1 times the outer diameter of the pipe, for easy interface operation. (3) The surface flatness deviation of the elevation control cushion layer should be ≤ 10mm, and the elevation error should be ± 20mm. The pipe can only be laid after being inspected and accepted by the supervisor. 5. Installation of double wall corrugated pipes (1) When the pipe lifting groove depth is ≤ 3m, manually lift the pipe into the groove. When the groove depth is>3m or the pipe diameter is ≥ DN400, use non-metallic ropes to slide the pipe, and it is strictly prohibited to hook the pipe mouth with metal ropes. After the pipe is in place, it should be temporarily fixed with sandbags to prevent rolling.
(2) The interface connection is installed from downstream to upstream, with the socket facing in the opposite direction of water flow. Before inserting the socket, apply soapy water to the inner wall of the socket and the surface of the rubber ring. For pipes with a diameter of DN400 or more, use a rope tensioner to assist in connection. The insertion depth should meet the design requirements, and the axis angle of adjacent pipe sections should be ≤ 2 °. (3) During the installation process of the elevation control double wall corrugated pipe, a level is used to track and measure the elevation error of the bottom of the pipe, which is ± 15mm, and the centerline deviation is ≤ 10mm. 6. Interface treatment: (1) Rubber ring installation: Insert the rubber ring into the groove between the second and third ripples of the socket, ensuring no twisting or rolling. Double sealing rings with a ripple interval, clean the surface of the socket with a clean towel before the interface. (2) After the sealing inspection is completed, use a feeler gauge to check the position of the rubber ring along the circumference of the interface, with a depth deviation of ≤

2mm. If necessary, use a strong flashlight to confirm that there is no gap. (3) After the temporary reinforcement interface is completed, symmetrically backfill medium coarse sand on both sides of the pipeline to the top of the pipe to prevent the interface from being displaced by external forces. 7. Construction of Inspection Well (1) Foundation Pouring: The foundation of the inspection well and the pipeline foundation are constructed simultaneously, using C25 concrete with the same thickness as the pipeline foundation, with a smooth surface and reserved connection holes. (2) The masonry blocks of the well body should be moistened in advance, the mortar fullness should be ≥ 90%, and the vertical deviation of the well wall should be ≤ 3mm/m.
Reserve a flexible interface at the connection with the pipeline, fill the surrounding area with sealing material and apply it in a "trumpet shape". (3) Installation of manhole cover: The elevation of the manhole cover should be consistent with the road surface. After the installation is stable, it should be fixed with C25 concrete. Within a range of 500mm around the well, graded sand and gravel should be backfilled and compacted. 8. Closed water test (1) Prepare to seal both ends of the pipeline using airbags or brick blocking plates. The bearing capacity of the blocking plate is calculated to be greater than the combined force of water pressure. Inject water into the upstream inspection well to the test head and soak for 24 hours to allow the pipe to fully absorb water.
(2) The observation standard test head is 2m above the top of the pipe, and the seepage volume is calculated according to Q=1.25 √ D (D is the pipe diameter). If the seepage volume does not exceed the allowable value and there is no leakage phenomenon after 30 minutes of observation, it is considered qualified. (3) Defect handling: When leakage is found, mark the location, repair the interface or replace the pipe after drainage, and retest until it is qualified.
9、 Backfilling and compaction (1) Within the range of 0.4m above the top of the backfill pipe, medium coarse sand is manually compacted layer by layer, with each layer thickness ≤ 200mm and compaction degree ≥ 95%. Mechanical backfilling can be used above 0.4m above the top of the pipe, but it must be done symmetrically from both sides, and unilateral pressure is prohibited. (2) Use a roller to compact the part above 0.7m on the top of the control pipe, with a compaction degree of ≥ 90%. The backfill material shall not contain stones or frozen soil blocks, and the temperature of the backfill soil during winter construction shall be ≥ 5 ℃. (3) During the process of protecting and backfilling finished products, avoid direct mechanical crushing of pipelines. Use small compaction equipment or manual compaction to promptly restore surface vegetation after backfilling. 10. Inspection and acceptance (1) Appearance inspection: The pipeline is straight, the interface is tight, the quality of the well masonry meets the requirements, and the well cover is firmly installed. (2) Verify and verify the material qualification certificate, test report, concealed engineering acceptance record and other documents to ensure completeness and completeness. (3) The functional testing closed water test is qualified, the pipeline slope and elevation meet the design requirements, and the number of backfill compaction testing points meets the specifications.

(4) After passing the acceptance inspection and filing, prepare the completion drawings, organize the construction materials and hand them over to the construction unit, and set permanent markings on the pipeline locations. 3、 Quality control measures 1. Material quality control measures: Before the pipes enter the site, they need to check the factory certificate of conformity and inspection report, and conduct mechanical property tests such as ring stiffness (≥ 8kN/m ²) and tensile strength (≥ 20MPa) by sampling according to batches. The appearance inspection needs to remove surface cracks, deformations, bubbles and other defects, and the size deviation of the socket should comply with the requirements of CJ/T225-2006 standard. The rubber ring should be matched with the pipe material, with good elasticity and no aging or cracks. Before installation, check the sealing with soapy water to ensure no air leakage. The material for the sand and gravel cushion layer should be medium coarse sand or graded sand and gravel with a mud content of ≤ 5%. Screening tests should be conducted upon arrival, and the particle size distribution should meet the design requirements. 2. Quality control measures during the construction process (1) The total station is used to locate the centerline of the pipeline for surveying and setting out. Control stakes are set every 5-10m, and a closed leveling point is introduced for elevation, with an error controlled within ± 10mm. The slope of the pipeline is strictly controlled according to the design value, with a permissible deviation of ± 0.5%. During the pipeline installation process, a level is used to track and measure the elevation of the inner bottom of the pipe. Each section of the pipe is measured at least 2 points, with a deviation controlled within ± 15mm. The axis deviation is checked by a theodolite or cable, with a deviation of ≤ 10mm every 10m. After positioning the inspection well, the relative position between the well position and the pipeline interface needs to be rechecked to avoid connection difficulties caused by deviation.

(2) When the trench excavation machinery excavates to a height of 200-300mm above the design elevation, manual cleaning of the trench shall be used. It is strictly prohibited to overexcavate and disturb the undisturbed soil. The width of the groove bottom is controlled by adding 300-600mm to the outer diameter of the pipe, and the slope gradient is determined according to geological conditions. For sandy or loose soil layers, the ratio is 1:1.5, and for clay, it can be steeped to 1:0.75. A 300mm × 300mm drainage ditch is set on both sides of the trench, with a collection well set every 50m. When the groundwater level is higher than the bottom of the trench, well points are used to reduce the water level to 0.5m below the bottom of the trench to prevent foundation softening. After excavation, check the bearing capacity of the bottom of the trench in a timely manner. Soft soil layers need to be replaced with graded sand and gravel and compacted with a compaction degree of ≥ 95%. (3) The sand and gravel cushion layer of the foundation treatment is evenly spread, with a thickness that meets the design requirements (generally 100mm for soil foundation and 200mm for soft soil foundation). It is compacted using a flat plate vibrator with a compaction degree of ≥ 95%. The surface flatness deviation of the cushion layer is ≤ 10mm, and the elevation error is ± 20mm. A groove with a length of 0.4-0.6m and a depth of 0.05-0.1m is reserved at the socket part, with a width of 1.1 times the outer diameter of the pipe to ensure the interface operation space. (4) The installation and hoisting of double wall corrugated pipes shall use non-metallic rope chutes, and it is strictly prohibited to hook the pipe mouth with metal ropes. Pipes with a diameter of DN400 or above should be connected with a rope tensioner as an auxiliary tool, and the insertion depth should meet the design requirements. The axis angle of adjacent pipe sections should be ≤ 2 °. Clean the surface of the socket before the interface, apply soap water lubricant, and install the rubber ring between the second and third ripples of the socket. The double sealing ring should be separated by one ripple. Use a feeler gauge to check the position of the rubber ring, and the depth deviation should be ≤ 2mm. After installation, use a sand bag to temporarily stabilize the pipe to prevent axis displacement. After the pipeline installation is completed, check that there are no debris inside the pipe and that the pipe opening is tightly sealed. (5) Construction of inspection well: The foundation of the inspection well and the pipeline foundation should be poured with C25 concrete at the same time, with the same thickness. Before construction, the blocks should be fully moistened, the mortar fullness should be ≥ 90%, and the vertical deviation of the well wall should be ≤ 3mm/m. The connection between the pipeline and the inspection well is sealed with flexible packing, and the interface is plastered in a "trumpet shape" with dense filling around it. The installation of the manhole cover should be smooth, with an elevation consistent with the road surface and an error of ± 5mm. After the completion of the well chamber masonry, the inner wall should be cleaned in a timely manner, and the smoothness of the flow channel should be checked to ensure that there is no accumulated water or debris. (6) Before the closed water test, seal both ends of the pipeline, and the bearing capacity of the blocking plate is calculated to be greater than the combined force of water pressure.
The test head is 2m above the top of the pipe. After soaking for 24 hours, observe the water leakage rate. If the water leakage rate Q is ≤ 1.25 √ D (L/(min · m)) and there is no water leakage, it is considered qualified.
During the experiment, record the water level drop every 30 minutes. If the leakage exceeds the standard, mark the leakage location, drain the water, repair or replace the pipe, and retest.
(7) Backfilling and compaction materials should be selected from medium coarse sand or graded sand and gravel. Within a range of 0.4m from the bottom to the top of the pipe, manual layer by layer compaction should be carried out, with each layer thickness ≤ 200mm and compaction degree ≥ 95%. Mechanical symmetrical backfilling shall be used above 0.4m of the pipe top, and unilateral pressure is prohibited. The part above 0.7m on the top of the pipe shall be compacted with a roller, with a compaction degree of ≥ 90%. The backfill material shall not contain stones or frozen soil blocks, and the temperature of the backfill soil during winter construction shall be ≥ 5 ℃. During the backfilling process, avoid direct mechanical compaction of the pipeline. Use small compaction equipment or manual compaction to ensure that the pipeline is not deformed or damaged. (8) Inspection and acceptance: During the construction process, self inspection, mutual inspection, and special inspection shall be carried out for each process, and concealed engineering acceptance records shall be filled out. After the excavation of the trench, the construction, design, geological survey, supervision, and construction parties jointly inspect the trench to confirm that the foundation bearing capacity and elevation meet the design requirements.
After the completion of the project, organize the construction materials and submit the acceptance application, including material qualification certificates, inspection reports, measurement records, closed water test records, etc. After passing the acceptance inspection, conduct completion measurement and draw completion drawings.
4、 Common quality problems, cause analysis and prevention measures

Common quality problems

Cause analysis

Prevention measures

Pipeline interface leakage groove settlement

Rubber ring aging, damage or improper installation;
; The interface is not cleaned thoroughly; Uneven application of lubricant
Insufficient compaction of backfill soil
; Untreated soft soil layer at the bottom of the trench; High groundwater level causes softening of the foundation. Choose high-quality rubber rings and check their quality before installation; Wipe the interface with a clean towel and apply soapy water; After installation, use a feeler gauge to check the position of the rubber ring. Strictly control the quality of the backfill soil, compact it layer by layer, and ensure that the thickness of each layer is ≤ 200mm. Soft foundations should be replaced or reinforced; Before construction, lower the groundwater level to 0.5m below the bottom of the trench. The pipeline floats. When the groundwater level is high, the buoyancy is greater than the weight of the pipeline; Precipitation before construction and timely backfilling after pipeline installation; When backfilling, it should be done symmetrically on both sides if the backfilling is not done in a timely manner or if the density of the backfill soil is insufficient. The bottom corner of the pipe should be filled with medium coarse sand to check for water seepage. The masonry mortar should not be full; When sealing the interface without masonry, ensure that the mortar is full, and use flexible filling material to seal the interface tightly; The manhole cover is not securely installed and sealed; The installation of the manhole cover should be smooth, and the surrounding area should be filled with mortar. 5. Finished product protection measures: 1. Protection measures during construction: The storage area for pipes should be flat to avoid sharp objects scratching the pipes. The pipes are stacked in layers, with each layer separated by wooden pads, and the height should not exceed 2 meters. When lowering the pipes, they should be lifted and placed gently to avoid colliding with the trench walls or other pipes. After pipeline installation, promptly seal the pipe mouth to prevent debris from entering.

When backfilling, avoid using large machinery to directly compact the pipeline, manual compaction or small-scale machinery to compact in layers. Backfilling materials shall not contain hard objects such as stones, bricks, etc.

2、 Protective measures after completion: Clear warning signs should be set up above the pipeline to prohibit heavy vehicles from crushing or stacking heavy objects. Regularly inspect pipelines and manholes, and promptly address any issues found. Avoid damaging pipelines during surrounding construction, such as taking protective measures when excavating other pipelines. During winter construction, insulation measures should be taken for pipelines to prevent freezing and cracking. Strengthen drainage during the rainy season to avoid long-term immersion of pipelines.