Budapest as model city for Spiral-Wound pipe rehabilitation in Europe

With the consistent application of Spiral-Wound technology along several kilometers and for several years, Budapest has developed into a model city for Spiral-Wound pipe rehabilitation in Europe. The individual versions of the technology are suitable for different rehabilitation requirements with various diameters and shapes of sewer networks. Since 2010, approx. 18,861 m lengths of round as well as custom shaped profiles have been rehabilitated in Hungary and thereof 5,869 m beneath the Budapest city centre. With the latest large profile rehabilitation project in the north-east of Budapest, the technology demonstrated again its wide range of capabilities. Sekisui SPR rehabilitated together with construction company Agriapipe 565 metres of the strong corroded cement pipe with dimensions of 1400 x 2100 mm underneath the Pozsonyi Street. From the end of June to the beginning of October 2014, the pipe rehabilitation team repaired the egg-shaped sewer while maintaining a controlled live flow using the SPR Spiral-Wound pipe method.

Spiral-Wound pipe system even suitable for egg-shaped sewer

The Spiral-Wound technology from Sekisui SPR is already a familiar rehabilitation method for the city of Budapest: approx. 18,861 metres of sewer pipes in Hungary and 5,869 m underneath the city life of Budapest have been successfully rehabilitated. Most recently, the Spiral-Wound pipe system has been employed in the trenchless rehabilitation of 54 m of the egg-shaped sewer underneath Pozsonyi Street in 2013, and of an additional 565 metres in the summer of 2014.

“Since the sewer network of Budapest features various diameters and shapes, the Spiral-Wound technology with its different method versions is the ideal solution for the operators. This provides a rehabilitation process for all standard diameters in circular form, but in particular, with SPR, also for the most diverse custom shapes, such as box or mouth-shaped, or even egg-shaped profiles, up to 5,500 mm,” commented Mr. Zoltán Varga, the Managing Director of Agriapipe Ltd, the construction partner. A central aspect in the selection of the Spiral-Wound method several years ago was also the requirement for the necessary structural integrity of the old structures to be re-established. Additionally it is an advantage that work can be carried out exclusively through existing manholes so that there are hardly any hindrances for the local residents as well as the street traffic of this megacity during the rehabilitation.

Variants of Spiral-Wound technology

The Spiral-Wound pipe method is based on the principle of the mechanical in-situ production of a liner made of extruded plastic profile strips. The process produces liners for nominal widths of 200 to 5,500 mm by a winding machine that pushes the Spiral-Wound profile in the host pipe or, depending on the process version, leads the Spiral-Wound liner through the structure. By standard, PVC-U profile strips are installed with the Spiral-Wound pipe technologies with differently structured locking systems, depending on the procedure. One exception is the SPR PE method in which an HDPE profile strip is used and the mechanical lock is replaced by a PE welding connection. The three Spiral-Wound pipe methods SPR, SPR EX and SPR RO, which have been used in Budapest for years as a model for future-oriented sewer rehabilitation, differ in particular according to two important features: On the one hand with regard to the static stability, on the other hand, the positioning of the winding machine in the winding process.

The Spiral-Wound pipe methods SPR EX and SPR RO wind the liner without annular space into the host pipe. In the end a close-fit liner with minimal cross-section reduction is created that allows an increased flow rate due to the low roughness of the material. If an annular space is created during the winding process, the necessary grouting with high-strength grout serves as a structural component on the SPR liner or with sealing material as insulation for the SPR PE method.

Host pipe condition class type II

Budapest Sewage Works Pte Ltd. operates the complete 5,400 km long sewer system of the metropolis. Underneath there is also a 730 m long cement pipe with a diameter of 1,400 x 2,100 mm that drains collected rain and wastewater of the district 13, in the north-east of Budapest into the wastewater treatment plant. The combined wastewater sewer, which has been in operation since 1907, exhibits material fatigue due to non-stop operation over the years as well as cracks and damage due to corrosion. Bacteria and caustic sulphuric acid inside the pipes have attacked the cement even though the concentration is low due to the common draining of wastewater and rainwater. The damage also decreased the structural stability of the concrete sewer.

The egg-shaped sewer in need of rehabilitation is located under the very busy main road, Pozsonyi Street, in the 13th district of downtown Budapest. In addition, buses come through every 5 minutes in the bus lane between the two lanes in each direction. For rehabilitation through standard manholes, only a few meters around the access needed to be blocked off for the equipment and the rehabilitation vehicle. There was hardly any hindrance for traffic above ground even though the rehabilitation project underground was rather large and many metres in length.

Winding process during controlled live flow

The 565 metre long ailing sewer section was rehabilitated with the SPR Spiral-Wound method by winding a steel-reinforced profile strip of PVC-U into a new highly resistant plastics inner layer directly within the host pipe. For that, the guide frame of the Spiral-Wound machine was lowered through a standard manhole into the rehabilitation section, installed into the host pipe directly and adjusted to the egg-shaped profile of the sewer while taking the statically required annular space into account. The 52 Spiral-Wound pipe spools stationed one after another above ground supplied the winding machine continuously with profile strips via the standard manhole. The winding machine moved forward with every rotation by one profile width and locked the profile with a tongue-and-groove mechanism to create a watertight liner. Once one of the 52 Spiral-Wound pipe spools was used up, the new profile strip was joined in a portable butt welding unit.

The winding process was carried out during controlled live flow in the old sewer. A masonry wall was built at the upstream point so that the pump could transfer the combined wastewater into the following sewer section. After about 250 metres of rehabilitated sewer section, the stone wall was moved from the upstream point into the middle of the rehabilitation section to control the live flow for the remaining metres to be rehabilitated. The goal was to maintain a water level of maximum 15 cm. Heavy rainfall posed a challenge occasionally as the water level rose to 1 metre and the winding process had to be interrupted briefly. Since the winding machine always remained stationed in the old sewer, winding could resume promptly after the water level had dropped and the pipe was cleaned.

Grouting

The winding process aimed to generate a defined annular space between the Spiral-Wound liner and the host pipe, which was filled with a high-strength grout in a subsequent work step. The thickness of the annular space is determined according to the following principle: as little annular space as possible, but as much annular space as necessary for the required static properties. In this case, the thickness was between 50 mm and 80 mm.

After the Spiral-Wound liner was completed, a bracing system was installed so that the annular space could be filled. The bracing frames positioned the Spiral-Wound pipe liner according to the static requirements and thus prevented buoyancy, a positional deviation and deformation during the subsequent grouting. The annular space was sealed after each 80-metre section of installation length and filled up in layers with special grout to re-establish the static features of each section.

Durable corrosion protection of the concrete structure

In the long term, the new rehabilitated pipe offers an important operational advantage: Since the steel-reinforced plastic Spiral-Wound pipe liner is not a temporary aid for installation, but rather remains a fixed design component of the rehabilitation solution, it permanently protects the host pipe and the filled-in annular space grout against mechanical abrasion and attack by the combined wastewater. In the end, the SPR Spiral-Wound pipe liner therefore serves as formwork for a new mineral grouting of the old sewer and as a reliable protective coating over many years that separates the concrete structure from the combined wastewater. The smooth and abrasion-resistant surface of the SPR liner will improve the hydraulic capacity minimum for the next 50 years of continuous operation and compensates for the minimal cross-section reduction of the host pipe.

As the final step, the reconnection of the grouting sections and laterals were done as usual. During this year’s rehabilitation project, the SPR technology not only proved to be durable and economic, but also a rehabilitation method that can be accomplished comparatively quickly. After the city ordered the works, successful completion of the rehabilitation of the sewer section was planned for just 15 weeks later on the construction schedule.