HDPE pipeline construction technology

Construction process: measurement → layout → trench excavation → foundation treatment → connection, pipe laying, pipe calibration → pipe trench backfilling → inspection well masonry, backfilling → acceptance. In addition to following construction specifications, the construction of HDPE pipes should also pay attention to the following characteristics of HDPE pipes:
(1) HDPE pipes have severe thermal expansion and contraction, so they should be constructed and used in environments with little temperature difference.
(2) When the buried depth of HDPE pipes is lower than the bottom surface of the building foundation, the pipes shall not be located within the range of foundation diffusion angle compression under the building foundation.
(3) In areas where the groundwater level is higher than the elevation of the excavated trench bottom, the groundwater level drops to 0.3 m to 0.5 m below the nearest point of the trench bottom.
(4) When excavating the pipe trench, the excavation depth should be strictly controlled and the undisturbed soil at the bottom layer of the foundation should not be disturbed. In case of over excavation or disturbance, natural graded sand and gravel with a particle size of 0.1 m to 0.5 m should be replaced and leveled and compacted.
(5) The HDPE pipeline foundation adopts gravel foundation instead of concrete foundation, with a thickness of 0.05 m to 20 m, depending on the geological conditions.
(6) During the pipeline laying process, the pipe is manually or lifted by a crane. When the crane lowers the pipe, non-metallic ropes are used to fasten the two ends of the pipe at a distance of 1/4 from the pipe mouth. It is strictly prohibited to lift the pipe through the hole.
(7) The requirements for backfill soil are relatively strict, and some backfill soil uses a certain specification of medium (coarse) sand (locally called asbestos sand). The hard edges of crushed stone (soil) are prone to damage the PE pipe and the backfill is not easy to compact. Asbestos sand has an automatic compaction function at the optimal moisture content, and can be compacted with small compaction equipment to meet the compaction requirements.
(8) Backfill the part above 0.7 meters on the top of the pipe using mechanical backfilling. Backfilling below the top of the pipe must be done simultaneously from both sides of the pipe and compacted, otherwise it is easy to cause uneven pressure on the HDPE pipe, resulting in deformation and displacement of the HDPE pipe. Other backfilling shall be carried out in accordance with the specifications.
(9) Connect the pipeline to the inspection well. In the original construction plan, the pipe mouth was recessed into the inner wall of the inspection well by 0.3 m to 0.5 m, painted with mortar into a "trumpet shape", and filled tightly with mortar around it. Then, bricks were laid, but the closed water test could not meet the requirements. After inspection, the following problems were found: ① The HDPE pipe's thermal expansion and contraction caused the inspection well to crack, resulting in water leakage from the inspection well. ② The inspection well was not cracked, but due to inadequate sealing at the connection between the pipeline and the inspection well, leakage and seepage occurred.