Description of a trenchless rehabilitation method
Cracking according to PN-EN 752-5; 13689; 1610
1. Method description
The cracking method consists in crushing the old sewer with adjustable expansion of the space (pieces of the old pipe are pressed into the ground) using a special head combined with a winch. Simultaneously, the new pipeline is pulled in after the crushing head or expansion head.
The liner is usually made of segmental pipe (PVC, PE) or continuous polyethylene pipe with reinforced outer surface. It is to protect the new pipeline against indentation or propagation of cracks.
2. Liner installation equipment
- sewer cleaning equipment (pressure truck)
- sewer inspection camera
- sewer milling machine
- pulling machine (pipe puller)
- heat welding machines (butt-welders and resistance welders)
- by-passing unit (pumps, hoses)
- testing equipment
3. Preparation to installation
Assessment of the sewer’s technical condition
Before starting rehabilitation, the pipeline is cleaned using a hydrodynamic sewer cleaning unit mounted on a truck. Then the pipeline is inspected using a remotely controlled camera. The video footage is used for preparing a detailed digital report on the pipeline’s technical condition. The report is a base for classifying the sewer’s technical condition.
Choice of the rehabilitation method
The rehabilitation method depends on the technical condition class and damage degree. After the assessment of the sewer’s technical condition, geodetic data have to be analyzed, including ground water level compared to the base of the sewer, motor traffic in the area, and other parameters that impact suitability of the trenchless rehabilitation method.
Storage and transport to the site
Pipes are delivered to a storage yard, where they are supplied from to the site in small batches.
4. Description of the installation process
The advantage of static cracking is possibility of replacing the old sewer with a new one of the same or larger diameter. The process consists in crushing the old sewer with adjustable expansion of the space (pieces of the old pipe are pressed into the ground) using a special head combined with a winch. Simultaneously, the new pipeline is pulled in after the crushing head or expansion head. Since the new main consists of short pipe sections, the joining process can be carried out inside the manhole, so there is not need of making additional installation pits. When the works are completed, the new sewer takes over all the functions of the old sewer, i.e. it is self-supported (it has durability sufficient for withstand any external and internal tensions) and ensures the required hydraulic capacity. Calibrated static cracking gives effects similar to rehabilitation of sewers using tight-fit or cured-in-place liners.
During rehabilitation using the cracking method the old pipeline structure is destroyed, so the inside of the new sewer is smoother and has no faults where the old sewer had section faulting or other breaches.
5. Inspection
5.1. TV Inspection
After the installation and opening connections, acceptance TV inspection (including VHS or CD recording) is carried out. Inspection report is also prepared.
5.2. Tests
According to PN-EN 13689, ISO 11296-1 and PN-EN 1610
6. Correction of flaws
Flaws are corrected using a robot controlled via a camera or / and inserting and gluing short pipe sections. In extreme cases a pit has to be made and a damaged section – replaced.
