What is a Helical Pipe Bursting

Helical pipe bursting is a trenchless pipeline replacement technique used to renew existing underground pipes by fracturing the old pipe while simultaneously installing a new pipe along the same alignment. The method uses a rotating, helical cutting head attached to a pulling system that breaks the host pipe outward into the surrounding ground. As the old pipe is displaced, a new pipe is drawn in behind the bursting head, taking its place without the need for continuous open excavation.

Within drainage and sewer engineering, helical pipe bursting is valued for its ability to replace deteriorated pipelines with minimal surface disruption. It is widely used for foul water, surface water, and combined sewers where traditional excavation would be disruptive, costly, or impractical.

Principle of operation and equipment

The core principle of helical pipe bursting lies in controlled mechanical fracturing. A helical bursting head, typically manufactured from hardened steel, is connected to a continuous pulling rod or cable system. The head incorporates spiral fins or blades that rotate as pulling force is applied. This rotation fractures brittle pipe materials and displaces fragments radially into the surrounding soil.

The pulling force is generated by a hydraulic power pack located at the reception pit. As the head advances through the existing pipe, the replacement pipe is pulled in behind it. The new pipe is usually a continuous length of polyethylene or another pressure-rated material capable of accommodating minor ground movement and providing long-term structural performance.

The rotational action of the helical head reduces peak bursting forces compared to static bursting methods. This makes the technique particularly effective in challenging ground conditions or where upsizing of the replacement pipe is required.

Applications in drainage and sewer renewal

Helical pipe bursting is primarily used for the replacement of ageing or structurally failed pipelines where repair or lining is no longer viable. It is suitable for pipes suffering from collapse, severe cracking, deformation, or chronic infiltration that cannot be addressed through internal rehabilitation.

The method is commonly applied to gravity sewers, rising mains, and private drainage laterals. It is effective for a wide range of diameters, from small domestic drains to larger municipal sewers. Helical pipe bursting is also used where an increase in pipe diameter is required to improve hydraulic capacity, provided surrounding ground conditions allow for controlled displacement.

Typical applications include:

• Replacement of brittle clay or concrete sewer pipes.

• Renewal of old cast iron or asbestos cement pipelines.

• Upsizing of undersized drains without widening trenches.

• Pipe replacement beneath roads, buildings, and landscaped areas.

Suitable pipe materials and ground conditions

Helical pipe bursting is best suited to pipes made from brittle materials that fracture cleanly when subjected to radial force. Clay, concrete, cast iron, and asbestos cement pipes are commonly replaced using this method. Flexible pipes such as polyethylene or PVC are less suitable as host pipes unless they are heavily degraded.

Ground conditions play a significant role in method selection. The surrounding soil must be capable of absorbing displaced pipe fragments without causing excessive ground heave or surface disturbance. Cohesive soils such as clay and compacted granular materials generally perform well. Loose or highly unstable ground may require additional assessment or alternative techniques.

Careful pre-construction investigation, including CCTV inspection and ground assessment, is essential to confirm suitability and manage risk.

Advantages over traditional excavation

One of the main advantages of helical pipe bursting is the significant reduction in surface disruption. Only small launch and reception pits are required, allowing roads, pavements, driveways, and structures to remain largely undisturbed. This minimises reinstatement costs, reduces programme duration, and limits impact on residents, businesses, and traffic.

The method also delivers a fully new pipe with structural capacity equivalent to or better than open-cut replacement. Unlike lining methods, which rely on the integrity of the host pipe to some degree, pipe bursting removes the old pipe entirely and replaces it with a new independent pipeline.

From an environmental and safety perspective, reduced excavation means less spoil generation, fewer vehicle movements, and lower risk associated with deep trench work.

Risks, limitations, and control measures

Despite its advantages, helical pipe bursting is not suitable for all situations. Pipes running very close to other services may pose a risk if ground displacement affects adjacent utilities. Similarly, shallow pipes beneath lightly loaded surfaces may cause heave if not properly assessed.

The technique requires precise alignment control. Significant changes in direction or multiple tight bends can complicate operations and may require additional access pits. Groundwater presence can also influence bursting performance and must be considered in design and planning.

Risk is managed through detailed surveys, careful selection of bursting head size, controlled pulling forces, and experienced operators. In sensitive locations, monitoring of ground movement may be implemented during installation.

Installation process and quality assurance

The helical pipe bursting process begins with the construction of launch and reception pits at either end of the replacement section. The existing pipe is exposed and prepared, and the new pipe is assembled or welded into a continuous length. The bursting head is attached to the pulling system and aligned within the host pipe.

As bursting progresses, hydraulic pressure and rotation are carefully controlled to maintain steady advancement. Once the head reaches the reception pit, the new pipe is fully installed. Connections to existing manholes or pipework are then completed, and the system is tested to confirm integrity and alignment.

Post-installation CCTV inspection is typically carried out to verify that the new pipe is correctly positioned and free from defects. This inspection forms part of the quality assurance record and supports long-term asset management.

Conclusion

Helical pipe bursting is a highly effective trenchless method for replacing failed or obsolete pipelines with minimal surface disruption. By fracturing the old pipe and simultaneously installing a new one, it provides a full structural renewal solution that overcomes many limitations of traditional excavation and lining techniques. When correctly specified and executed, helical pipe bursting delivers long-term reliability, improved hydraulic performance, and significant social and environmental benefits. In modern drainage and sewer renewal programmes, it represents a key technology for extending asset life while minimising disruption and cost.