Technology for laying HDPE pipes in the ground: main steps and tools

The construction of utilities using HDPE pipes laid in the ground is the most widely used technology today. Products made from this material are replacing the old steel ones.

The technology of installing the pipeline in the ground has also changed. Step-by-step instructions for building an underground polyethylene line and knowing what is needed for this will help you do this work yourself.

Features, pros and cons of HDPE pipes

HDPE (low pressure polyethylene) is a modern, high-quality polymer, products from which are in great demand in the construction of engineering networks.

The main positive characteristics of polyethylene products include:

• the ability to withstand increased internal pressure (depending on the parameters of the assortment — up to 10 MPa);
• low density of the material and therefore low weight of the product;
• resistance to expansion under the influence of heat (no more than 3% at maximum allowable temperatures);
• lack of response to the effects of chemically active substances and reagents;
• relatively low price;
• long service life — up to 50 years.

The disadvantage of polyethylene products is a limited operating temperature range: from 0 to 40^aboutFROM.

At low temperatures, the pipes become brittle, which can lead to their breakage.

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Under the influence of high ambient temperatures, the opposite phenomenon occurs — the material softens and loses the necessary operational rigidity.

This disadvantage makes it undesirable to use pipes made of polymers in open areas and puts forward the requirement for their laying in the ground below the freezing point or with insulation.

How to prepare a trench for laying a highway

Having put the communication construction plan on paper, you can proceed to its practical implementation.

Work on laying a route from HDPE pipes in the ground begins with trench equipment.

In this case, the following conditions must be met:

• the depth of the trench should be such that the communications lie at least 0.5 m below the freezing level of the soil;
• at the bottom of the trench, a sand cushion is equipped (in solid ground) or fine gravel is added (on loose soils).

Such a cushion not only levels the bottom of the trench, but also protects the line from deformation under load.

Polyethylene sewerage is not recommended to be made at a depth of more than 2.5 m.

Step-by-step trench device algorithm:

1. Marking, according to the plan, of the pipeline route along the cord;
2. Soil excavation (manually or using special equipment).
3. Preparation of the bottom of the track (compaction and cushion equipment).

The technology of laying HDPE pipes during the construction of sewer systems assumes, as a general rule, the presence of a slope of 1-2 degrees per meter of length.

The width of the trench is selected taking into account the convenience of performing installation work.

How to lay pipes in the ground

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Installation starts from the point of water or wastewater intake. The prepared material is preliminarily laid along the edge of the trench.

In pipes with a socket, it is important to choose the direction of the socket correctly — opposite to the drain.

Further, the installation process is as follows:

• cleaning of sockets and joints;
• mark of the maximum depth of the pipe entry into the socket;
• docking the end of one pipe with the socket of the other, but not all the way — with a mandatory gap of 1 cm.

You need to focus on the mark made. Such a gap is necessary to compensate for spontaneous deformations of the track.

When building a communication from polyethylene at a depth close to the freezing point, it is necessary to insulate it. With the trench method of laying, polyethylene foam is often used for insulation.

This insulation has excellent properties of thermal insulation and vapor permeability, has good density and elasticity.

How to seal pipe connections

The tightness of the HDPE pipe system is ensured by rubber seals. When laying an underground pipeline, it is necessary to ensure its additional sealing in the places of socket connections. This is dictated by the difficulties in determining the malfunction and repairing the system in case of leaks or ingress of groundwater into it.

Silicone sealing

Polymer sealants are used to seal joints. The most popular of them is silicone, which includes rubber. In working condition, this material has good elasticity, a high degree of adhesion and can withstand heavy loads.

On the market, you can choose a sealant for specific operating conditions of sewer or water systems.

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The composition is applied without gaps on the inside of the socket and the outer section of the pipe joined to it, and after the connection it is necessary to lay the sealant around the entire circumference and on the outer part of the joint. The seam is leveled with a soft spatula or a moistened gloved finger.

Important! After joining the pipes with silicone sealant, it is necessary to ensure the immobility of the joints for at least 4-6 hours.

Sealing with self-adhesive tape

Self-adhesive tape is effective for sealing pipe bends, plugs, tie-ins or bends. Its composition includes bitumen-polymer materials, which ensures complete water tightness.

Working with the tape is easy:

1. Prepare sections of pipe connections by cleaning them of dirt and treating them with a primer.
2. Wind the tape at constant tension with 50% overlap on the joint area, avoiding wrinkles and distortions.

The tape is applied to a dry surface with a mastic layer inward in a spiral.

Advantages of sealing tape:

• long service life with preservation of tightness — more than 30 years;
• exclusion of deformation with proper application;
• mechanical strength and resistance to chemicals and soil corrosion.

To seal the communication route in the ground, it is better to use a winter tape with the letter «З» in the marking.

Pipe connection methods

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The HDPE pipeline can be mounted in detachable and one-piece methods.

Split method

This is the simplest version of pipe connections. It involves bell-shaped or fitting pairing.

For fastening to the socket, special elastic seals are used. This method does not give one hundred percent tightness, therefore it is used in the construction of non-pressure networks.

A more reliable way to install a polyethylene line is using fittings.

Compression fittings are used when installing pipes of small diameters — up to 63 mm.

Required accessories for detachable mounting:

• hacksaw or pruner knife;
• calibrator or sandpaper — for chamfering;
• mounting key for HDPE fittings;
• manual or electric pressing tongs.

For professional work, you can buy more expensive equipment — a manual hydraulic press.

One-piece method

Pipes of larger diameter are welded: butt-welded or using electric couplings.

For butt welding, pipes are laid in a special apparatus, which fixes them, and then heats them up, bringing the ends to a viscous state. Then they are pressed with force and welded to each other.

Electrofusion welding is performed using special connectors and is not very difficult. A low-temperature electric spiral is mounted inside the shaped elements, which heats up under voltage and welds the couplings.

For welding HDPE pipes, a special apparatus is required. Such compact machines are not cheap equipment, and are usually used by professional craftsmen. The acquisition of a welding unit for one-time work is not rational.

The method by welding allows the installation of the route in cramped conditions.

Regulatory requirements SNiP

The requirements of SNiP for the width of the trench for laying pipes with a diameter of up to 0.5 m are as follows:

Connection type	trench width
Welded	D + 0.5 m (D — pipe diameter)
Bell-shaped	D+0.6 m
Flanged	D+0.8 m

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For the installation of HDPE pipes, SNiP established:

• Welding work must not be carried out at temperatures below 10^aboutFROM;
• The welding area must be protected from rain, dust and dirt.

It is forbidden to weld pipes and couplings from different materials.

How to close a trench

With the seeming simplicity of the issue of backfilling the trench after the installation of the highway, these works should be taken very responsibly and competently.

To close the trench, you can use the soil removed during digging, if it is sufficiently clean and loose. Large stones, larger than 2.5-3 cm, must be removed from the ground.

When re-laying the soil, you must follow the basic rules:

• to carry out work slowly and accurately;
• do not pour earth immediately onto the pipeline, but lay and compact in layers of 10 cm on both sides of the pipeline, fixing it horizontally.

Small gravel or crushed stone can be used for compaction, alternating backfill in layers with soil.

Important! Do not apply excessive force to compact the soil directly above the pipeline.

Use of HDPE pipes for cable protection

HDPE pipes are widely used for cable laying.

Corrugated double-walled pipes are often used in cable communications underground. They are strong, have good ring stiffness and are elastic.

Taking into account the technology of building a cable line, pipes can be supplied with a cable pulling probe.

When laying electrical cables in building structures, special corrugated polyethylene products can be used.

The cable can also be laid in ordinary communications from HDPE, with fitting connections.

Communications are fixed on pre-selected sections of the structure, then a cable is pulled through them.

Possible difficulties and advice from the masters

In the underground construction of a polyethylene highway, some difficulties may be encountered. These include:

• soil features (stony, unsteadiness, moisture, waterlogging, heaving);
• high location of groundwater;
• location of other underground utilities on the route.

Therefore, before starting work, it is necessary to conduct the necessary studies and take everything into account at the design stage.

Experienced craftsmen also advise:

• tighten the fittings with care, without excessive effort;
• the discrepancy in the cross section of the welded pipes should not exceed 10%;
• butt welding of polyethylene products to do with one seam.

Following the above tips and observing the technology for building communications from HDPE pipes will ensure the reliability, functionality and long-term operation of engineering systems.