According to 14148 standard's definition, manhole is a vertical and waterstop structure which is used in the courses of sewer and gravity drainage.
The purpose of this structure is:
- Human and equipment access to underground facilities for inspection, removing the obstruction, aeration and ventilation of underground networks
- Aeration and ventilation of underground networks
- Making connections in sewer pipelines
- Changing direction, height and slope in the sewer pipelines
- Changing the diameter of the sewage pipes
Using common bricks and concrete manholes have always had some problems. That is why with the increase the usage of polymers in the polyethylene manholes industries which produced by technology of rotary molding replaced traditional manholes. Tapers decreases from at least one meter diagonal to 60cm diagonal for the inlet valve.
This manholes produced by technology of Rotary Molding.
In fact, for the following reasons, the use of these polyethylene manholes are more common in recent years:
- The lower cost of installing and implementation
- High installation and implementation speed of polyethylene manhole
- Compatible with various of sewage and drainage systems
- long working life of over 50 years especially in wet areas
- High resistance to acidic and basic substances located in sewages
- Not losing the pressure in the flow due to the smoothness of the watercourse's surface
- Lower maintenance costs
- Complete network sealing and preventing the penetration of subsurface water into the sewage system
- Not leaking the sewage to the underground aquifers
- Earthquake and flood resistant
Polyethylene Grade 3840
In the productions of rotational molding materials, especially manholes, Polyethylene Grade 3840, with extraordinary properties, is been used. In Iran, this material is produced in Tabriz and Arak refineries.
The following table shows the produced polyethylene specifications in domestic refineries. The melt flow index (MFI) is 4 and the density of this polyethylene is 0.938.
Table 1 - Specifications of polyethylene produced in domestic refineries
This material is recyclable and its polymeric chains are very compact, this causes to increase the density. Therefore, its mechanical resistance increases and the compression of polymeric chains makes it resistant to chemicals and environmental stress cracking.
At first, this material is colorless and non-transparent. In order to use it, pigment can be added. The inner and outer surfaces of the manhole must be smooth, clean and flawless.
The color of the manhole can be any color, however, the color must be uniform throughout all its surface.
Polyethylene 3840 produced in domestic refineries has thermal, light and color stabilizing additives.
According to Iran national standard 14148, the P-R polyethylene manholes have the conditions to be used outdoor for at least one year and that is why its ingredients contain anti-UV additives.
According to 14387 national standard, which itself is provided according to 1759 ASTM standard, polyethylene manhole must withstand against horizontal loads (radial) and also vertical loads (axial) due to soil weight and the loads on it. Based on this, the filler around the manhole (backfill) must be prepared and executed that tolerates these loads with the polyethylene manhole structure without losing its stability during operation over the years.
Connecting solid and perforated pipes to manhole
In order to connect solid and perforated pipes to manhole, we should just find the exact place of the pipe connection to the manhole after setting the pipe height and the distance of it to the manhole's floor. Then, create a hole with more than 1cm diameter with gimlet or saw and after attaching the sealing washer, connect the solid or perforated coupler pipe to that.