Large-Diameter Pipeline and Manhole Rehabilitation

Application to large-diameter networks

Rehabilitation techniques for large-diameter pipelines and manholes are probably among the oldest forms of trenchless technology.

Before CCTV equipment made inspection of small pipes possible, larger pipelines could already be entered by walking or crawling, and in many cases conventional masonry or concrete repair techniques could be applied manually underground.

Conditions for man entry

The definition of a pipeline suitable for man entry varies from country to country.

In general, personnel can work inside circular pipes of around 900 mm diameter or larger, or non-circular pipes larger than approximately 900 × 600 mm.

Work in smaller spaces may be subject to highly restrictive safety procedures.

Confined-space safety

Properly trained specialist search-and-rescue teams are essential for this type of work.

Conventional emergency services are generally equipped primarily for rescuing people from buildings rather than confined underground spaces.

Their equipment may also be too bulky to enter pipelines and manholes below certain dimensions.

Systems applicable to larger diameters

Many rehabilitation systems developed mainly for smaller-diameter networks can also be applied to larger pipelines.

However, economics may be unfavorable because of the quantity and cost of materials required.

Pipelines, manholes and infiltration

Rehabilitation should address not only pipelines but also the manholes located along them.

There is little benefit in sealing pipelines against groundwater infiltration and sewage exfiltration if manholes continue to leak.

Sealing a pipeline against groundwater infiltration may also increase external pressure and infiltration into manholes, so manhole rehabilitation should be considered an integral part of the process.

Prefabricated components and in-situ work

As with smaller pipes, rehabilitation of large-diameter pipelines and manholes can be divided between systems using prefabricated components and techniques constructed or cured in situ.

The choice depends on the condition of the existing structure, available access, safety requirements and the technical and economic feasibility of the intervention.