Trenchless sewer rehabilitation – State-of-the-art spiral-wound pipe rehabilitation technology

Where pipe lining and short pipe lining processes come up against insurmountable operating limits in terms of nominal diameter and profile type, the latest spiral-wound pipe lining method almost always offers a technically satisfying and above all cost-effective problem solution.

 

Ideally, trenchless (or “no-dig”) sewer rehabilitation processes, by definition, are installed without any disruption of the surface or intrusion in the subsoil whatsoever. The trenchless pipe rehabilitation method with the currently most potential for development is the so-called spiral-wound pipe lining. With this method the liner is produced in situ by winding an endless profile strip fed through the inspection shaft to form a pipe. The spiral-wound pipe lining was developed in 1978 under the name SPIREX and marketed for the first time under the name Rib Loc in Australia in 1979.

 

The spirally wounded new pipe is produced by a winding machine, which is positioned in the shaft and, depending on the process used, either pushes the growing spiral-wound pipe in or pulls it through the pipe or structure. This technical solution is made possible by the design of the profile strip, the windings of which have friction and positive tongue-and-groove locking. In special cases the tongueand-groove locking is replaced by a welded joint.

 

Structural and process engineering features which distinguish the various versions of spiral-wound pipe liner in the sewer pipe:

 

The available spiral-wound pipe technologies are ideal for the limited dimensions of the structures to be rehabilitated. Below a certain dimension – approx. DN 800 – even CIPP liners are difficult to fit through shaft structures. In most cases the shaft cone is then removed or work is performed using an installation trench. These trenches are normal procedure for lining short pipe sections in nominal sizes large enough to permit the passage of persons. The endless profile strip for a spiralwound pipe, on the other hand, always fits through the inspection shaft, irrespective of the size of the structure. So ultimately, spiral-wound pipe technology is the most minimally invasive rehabilitation solution on the market.

 

The “technological forefather” of all spiral-wound pipe processes was a system developed in Australia in 1978, in which a PVC profile strip with double tongueand- groove locking was wound from a stationary winding machine situated in the shaft to form a liner with a fixed diameter in the old pipe. From this original form, several practical techniques have evolved over the years, which are now marketed almost exclusively by the SPR Group and deployed by subsidiaries KMG and Rabmer in Europe, Heitkamp in the USA as well as licensed partners in Asia. With its SPR™ technology the SPR (SEKISUI Pipe Rehabilitation) Group has itself made a major contribution to the further development of spiral-wound pipe lining.

 

Due to occasional demand for a flexible liner that could be adapted to varying nominal widths of the old pipe, SEKISUI Rib Loc developed another type that is currently in use as SPR™ EX. As the original name suggests, this spiral-wound pipe is capable of expansion. It employs PVC, but this time the profile strip has double tongue-and-groove locking. One of the two locks – the primary lock – can slide, while the secondary lock is bonded during the winding process. The profile incorporates a cutting wire, which is wound as well. The SPR™ EX liner is undersized when wound – from the start shaft, as usual – into the pipe. When the target shaft is reached, the cutting wire is pulled. This progressively cuts the bonded secondary lock along its entire length, thereby “unlocking” it. When the liner is fixed in place in the end shaft and the profile wound from the start shaft, the liner slides in the primary lock and expands radially until it lies against the wall of the pipe as a close fit. Minor differences in dimensions can also be overcome by this method. SPR™ EX is used in circular profiles in the range DN 200 to DN 750.

 

With SPR™ RO (familiar on the market as the ROTALOC method), a liner is produced from a PVC profile strip. The technique can currently be used in circular profiles DN 800 to DN 1800 and the material used for the old pipe is irrelevant. The system itself is based on an endless PVC profile reinforced by T-bars, with single tongue-and-groove profile locking which ensures lasting friction locking of the system in the windings. In the SPR™ RO method, the winding machine is selfpropelled and winds the liner in the sewer as a close fit until it reaches the end shaft. The profile strip is fed continuously from a reel on the surface and processed in the winding machine.

 

The SPR™ PE (RIBLINE) system uses different material and a different process. Here, the processed profile strip consists not of PVC, but of HDPE, which is reinforced with fully encapsulated steel strips.

 

The profile is not joined via tongue-and-groove locking, but continuously welded by an extrusion welding machine connected to the winding machine. In this case, the winding unit is stationary in the shaft and the resulting liner is fed and wound into the sewer ahead of it. The annular space is sealed in order to stabilise the position of the liner. As SPR™ PE can currently be used for sizes up to DN 3000, in some cases also using existing standard shafts, in this diameter range the system is a virtually unrivalled trenchless rehabilitation technique in many fields of application.

 

A giant step in the evolution of spiral-wound pipe technology was the development of the SPR™ process by the SEKISUI Chemical Co. Ltd. The fundamental difference between this method and the original Australian process is that SPR™ permits pipes of any geometry to be wound – up to a nominal diameter of DN 5500. The material used in the SPR™ process is PVC, whereby a w-shaped steel profile is integrated in the profile strip for the purpose of reinforcement. Here, as with SPR™ RO (ROTALOC), the winding frame is not stationary in the shaft, but moves through the structure ahead of the liner. Thus, with SPR™ no friction is produced between the liner and the pipe wall. As a result, pipes of considerable length can be wound from a single access point. The only factor restricting the length is the backfilling of the annular space.

 

The static capacity of the SPR™ system, however, does not depend solely on the spiral-wound pipe. It is purposely installed with a precisely defined amount of undersize and exactly centred when secured in the sewer. Finally, a system of spacers ensures that the required annular space is uniform throughout. The intentional annular space produced is filled section by section with fast-flowing, quick-setting special mortar during the winding process. The SPR™ liner therefore acts as a shell, so to speak, for a new mineral wall for the structure – and its strength alone dictates the static performance data of the entire system! The new wall is also permanently separated from the sewage by the PVC liner, which remains in the sewer. An SPR™ liner eliminates the preconditions for attacks of sulphuric acid on unprotected, cement-bound surfaces, which therefore clearly distinguishes this option from traditional methods of structural rehabilitation, such as mortar or jetcrete coatings.

 

As a standard inspection shaft is sufficient as access for the winding frame and profile strip, SPR™ often proves to be the only rehabilitation solution for problematic large profile structures with extremely poor accessibility – especially in cases where a trench is absolutely not an option. A further advantage is that bends can also be achieved with SPR™ liners. This caters for the fact that historical central sewage systems in cities were not always built in straight lines from one shaft to another, bends being very frequent.