Application of HDPE Pipe in Municipal Engineering

Physical and chemical properties of HDPE pipes

HDPE pipe is made of high-density polyethylene material, and its main features are as follows:

(1) It has good chemical stability and environmental protection, is non-toxic and pollution-free, and is not conducive to the reproduction of algae and bacteria. According to the test, it is not corroded by any organic and inorganic substances at 20°C; Sulfuric acid, concentrated nitric acid, chlorine, bromine, halogen substances and other strong oxidants contact for a long time, although they will be decomposed into Hydrogen, Halide compounds, but still maintain the original molecular structure; Hydrocarbons and their halides will cause the pipe body to swell. 

(2) High strength and good flexibility. Strong recovery ability after deformation, and can withstand strong external impact. Under the condition of 5% deformation, when the trench compaction degree is 85% to 95%, the buried thickness of the soil layer can reach 11m; after the pipeline is buried, even if the terrain has a large settlement deformation, it will not break. 

(3) It has good low temperature characteristics and sun resistance. Its effective use temperature is generally -40-60°C, and it will not freeze and crack when the temperature is -80 qc. 

(4) The pipe wall is smooth, the friction coefficient of the inner surface is small (n=0.010~0.011), the energy consumption of drainage is low, and the unit flow capacity is large. 

(5) The service life is long, and the buried service life can reach 40-50 years, and the raw materials are renewable. 

(6) Light in weight, its weight is only equivalent to 10% of the weight of the concrete pipe of the same specification. Good wear resistance, convenient transportation, when the installation angle is small, the laying and installation of pipelines are also very convenient, the welding process is simple, and the comprehensive unit price of the project is low.

HDPE Water Pipe Construction

The construction process of HDPE pipe is as follows: Trench excavation—pipeline entry inspection—groove acceptance—pipe lower groove laying—pipeline connection—pipeline and inspection chamber connection—pipeline tightness test—pipeline

Backfill a project acceptance.

(1) Trench excavation. The excavation width of the trench is related to factors such as pipe diameter, degree of compaction, and operation safety. The smaller the width, the less the excavation and backfilling workload of the earthwork, the lower the construction cost, and at the same time, the earth pressure on the pipeline will also be reduced. Therefore, the excavation width of the trench should be reduced as much as possible without affecting the pipeline installation.

(2) Pipe foundation. Because the hdpe water pipe is made by winding method, the elastic response is strong. In soft soil areas where uneven subsidence often occurs, damage or detachment will generally not occur after construction is completed. However, in order to maximize the characteristics of the pipeline and the effective fractional load, the pipeline foundation should be treated in the following ways at different foundations: a. For a good foundation, when the compaction effect is the same as the original soil foundation, no foundation layer is required; when the compaction effect is lower than the original soil foundation, it is best to set a sand or high-quality soil cushion with a thickness not less than 15 cm; b. For ordinary foundations that may have uneven settlement, it is best to set up sand or high-quality soil cushions with a thickness not less than 15 cm (DN=250-450mm), plus cm (DN=500-900mm and 30 cm (Dc≥1000 mm) ; c. For soft foundations, in principle, coarse sand cushions should be set up, with a base width of 2-3Dc and a base thickness of 15-30 cm or more; d. For rock foundations, high-quality soil cushions should be set up to maximize To avoid stress concentration on the bottom of the pipe, when the pipe foundation width is ≥ Dc+20 cm, the foundation thickness should be ≥ 30 cm; when the buried height is ≥ 7 m, the foundation thickness should be increased by 4 cm for every 1 m of buried height.

(3) Pipe connection. Pipes are generally connected by electrofusion, and large-diameter pipes are connected by socket connection. The connection sequence of electrofusion connection method is as follows: a. In order to facilitate construction, place the pipe at a certain height (above 30 cm) to keep it level and align the joints; b. Thoroughly remove dirt and other dirt on the surface of the water poly pipe connected to 1:3; c. With the butt joint of the pipeline as the center, the PE tape is wound and bonded; d. Connect the outer steel clip fixing plate at the end of the PE belt, and connect it with crucible screws

Connect Ie to connect the power supply at both ends of the PE belt, and the power required for electrofusion connection and electrofusion connection is 20 KW, and the time is about 15 minutes

(4) Trench backfilling. The pipeline trench should be backfilled with high-quality soil with good compressibility, and hard rocks, pointed rocks, and rich-rich soil that will cause uneven settlement must not be used to damage the water poly pipe.

Organic material taxi backfill. The degree of compaction toward the groove wall directly affects the deformation of the pipeline, so the compaction of the two groove walls must be done carefully. The compaction of the top part of the pipe should be carried out after the backfill thickness reaches 25-30 cm. When the top thickness is less than 30cm, it should be compacted manually or by small machinery; when the top thickness exceeds 30cm, large-scale engineering equipment can be used to avoid deformation of the pipeline to the greatest extent.

(5) The buried depth of the pipeline. The burial depth of the pipeline is related to factors such as the purpose of the pipeline, flow rate, depth of frozen soil, buried objects and loads, etc. The burial depth should not cause deformation and function of the pipeline. Considering the influence of factors such as frozen soil depth and road surface load, the minimum buried depth should not be less than 0.7 m in principle. When the burial depth does not meet the design requirements, appropriate protective measures shall be provided on the top of the pipe.

(6) The inspection well is not set. Inspection wells should be set at the starting point of the pipeline, where the inclination and the diameter of the pipeline change, at the corner, where there is a step difference, where the pipeline meets or where maintenance of the pipeline is required.

(7) The connection between the pipeline and the inspection manhole. Due to the difference in shrinkage between concrete and HDPE water pipes, there will be gaps between the pipes and concrete when they are directly connected, resulting in leakage. In order to avoid leakage, a lip seal should be installed at the joint between the pipe and the inspection well.

Practical Application of Water Poly Pipe

In the "cleaning and diversion of sewage" improvement project of Cailian River in Rendian River in Kunming, which started in February 2022, in order to achieve the purpose of rain and sewage diversion, sewage interceptors and water interception ditches are installed on both sides of Cailian River. As far as the second tender section is concerned, the total mileage of the sewage interceptor is 5 326.82 m. Considering the poor geological conditions along the Cailian River, the sewage interceptors are basically located on the peat soil layer. In order to reduce the impact of the pipe weight on the foundation, the original design selected FRP sand pipes. After a period of construction, it was found that due to the poor toughness of the FRP sand-filled pipe, the high requirements for the treatment of the foundation, the long construction period of the foundation, the different shrinkage of the pipe and the inspection well, and the uneven settlement of the foundation, the pipe and brick laying Check that all connections between wells are broken. Even some inspection wells were cracked and damaged. Although the connection between the pipe and the inspection well was improved, the closed water test still failed to meet the requirements stipulated in the standard. The engineering headquarters comprehensively considered the construction period, After factors such as project quality, economy and minimizing the impact of the sewage interceptor construction on the residential buildings along the line and the existing embankment, it was decided on September 2, 2002 that the right side of the ecological river embankment of the first contract section and the second contract section From Xinkaihe to Chahe, the right FRP central sand pipe was changed to HDPE water pipe. After that, the new pipes are all made of HDPE water pipes.