HDPE double-wall corrugated pipe municipal drainage construction plan: trench excavation and backfill compaction

HDPE double-wall corrugated pipe is widely used in municipal drainage engineering due to its excellent ring stiffness and anti-deformation ability. The quality of trench excavation and backfill compaction directly affects the service life of the pipeline, and it is necessary to strictly follow the construction specifications. The following describes the key points from the three aspects of construction preparation, excavation process and backfill technology.

Pre-construction preparation

Before construction, the site investigation needs to be completed, the axis positioning is carried out by the total station, and the trench excavation sideline and elevation control line are released. Focus on checking the distribution map of underground pipelines, and use manual pit exploration to confirm the location of surrounding gas, electricity and other pipelines, and maintain a safe distance. For soft soil layer or areas with high groundwater level, a light well point precipitation system needs to be set up in advance to ensure that the groundwater level is reduced to 0.5m below the bottom of the tank. At the same time, prepare backfill materials such as graded sand and gravel, medium and coarse sand, etc. The mud content should be 5%, and the maximum particle size should not exceed 50mm.

Key technology for trench excavation

Select the excavation method according to the soil type: Sandy soil adopts 0.5:1 sloping combined with steel sheet pile support, and the clay soil can be naturally sloped at 1:0.75. Reserve 20cm of artificial bottom cleaning during mechanical excavation to avoid over-excavation disturbing the base soil. The width of the bottom of the trench is determined according to "pipe outer diameter + 0.6m working surface". When the depth exceeds 5m, a stepped slope is set with a step width of 0.5m. The acceptance of the bottom of the trench needs to meet the flatness of 20mm/2m and the bearing capacity is 120kPa. The unqualified area is treated with graded crushed stone replacement. The thickness of layered compaction is 300mm.

Backfill compaction quality control

Backfill is implemented in three areas: the axillary angle of the bottom of the pipe is symmetrically backfilled with medium coarse sand, and it is compacted with a plug-in vibrating rammer; light roller is used in the range of 50cm below the top of the pipe, and the compaction degree is 90%; vibrating roller is used for layered rolling from the top of the pipe to the ground. The thickness of each layer of virtual pavement is 250-300mm, and the compaction degree reaches 95%. During the compaction process, the vertical deformation of the pipeline is monitored. When the diameter of the pipe is 800mm, the deformation amount shall not exceed 3%, and asymmetric backfilling on both sides of the pipeline is strictly prohibited. During the rainy season, trench drainage should be done well, and the moisture content of the backfill soil should be controlled within the range

Quality acceptance standard

Groove acceptance key inspection: the bottom of the groove elevation deviation is 30mm, the median line displacement is 50mm, and the slope slope meets the design requirements. The backfill compaction degree is tested by the ring knife method, and 3 groups of samples are taken every 50m. After the pipeline is installed, the closed water test is carried out. The test water head is 2m above the top of the pipe, and the water seepage should be 0.05m ³/(h · km). The whole construction process adopts BIM technology for three-dimensional disclosure. Real-time monitoring of trench settlement and pipeline displacement through the smart construction site system ensures that the construction quality meets the requirements of the "Technical Regulations for Buried Polyethylene Drainage Pipeline Engineering" (CJJ/T 29-2010).

Through scientific planning of the excavation process and strict control of backfill materials and compaction parameters, the uneven settlement of HDPE pipelines can be effectively avoided. In the actual construction, it is necessary to combine the dynamic adjustment plan of geological conditions, pay special attention to the drainage in rainy season and the anti-freezing measures in winter, and ensure the long-term stable operation of the municipal drainage system.