Pipe Jacking Association
10 Greycoat Place
London SW1P 1SB

Telephone
+44 (0)845 0705201

Facsimile
+44 (0)845 0705202

Email
andrew.marshall@pipejacking.org

The major applications for pipe jacking and microtunnelling include new sewerage and drainage construction, sewer replacement and lining, gas and water mains, oil pipelines, electricity and telecommunications’ cable installation, and culverts. Special applications include the installation of
rectangular or circular sections for pedestrian subways, road underpasses and bridge abutments. The technique can be used to negotiate obstacles such as motorways, railways, rivers, canals, buildings and airfields in the path of pipe laying projects; to minimise the surface disruption frequently associated with open cut pipe laying methods in urban areas; or simply to
provide a permanent underground tunnel construction. Pipe jacking is primarily used as an alternative to open cut excavations or other tunnelling methods. Significant lengths are attainable at larger diameters using mechanised techniques. Reference should be made to Tables 4c and 4d for specific recommendations. Construction methods are available to cope with both cohesive and non-cohesive soils in dry or water bearing
conditions. Excavation techniques are also available for jacking through rock or mixed ground conditions, including cobbles and boulders.

Technical Benefits
Technical benefits associated with pipe jacking are:

• Inherent strength of lining
• Smooth internal finish giving good flow characteristics
• No requirement for secondary lining
• Considerably less joints than a segmental tunnel
• Prevention of ground water ingress by use of pipes
  with sealed flexible joints
• Provision of invert channels in larger pipes to contain
  the dry weather flow of a sewer in a combined system
• Less risk of settlement
• Minimal surface disruption
• Minimal reinstatement
• Reduced requirement for utilities diversions
  in urban areas

Safety Benefits
Pipe jacking is an inherently safer method of working than open trench construction or traditional segmental tunnelling. When considering the risks associated with deep, large section, open excavations, Health and Safety Executive guidance suggests these risks should be reduced “if appropriate using ‘trenchless’ technology to avoid the need to excavate the trench in the first place”. Given gang size differences between the techniques and the resulting reduction in man-hours, opportunities for
accidents to occur are less with pipe jacking. There is also significant reduction in the risk of injury as a result of utility strikes and interface with the public.

Environmental Benefits
There are substantial environmental benefits to be gained by the use of pipe jacking techniques when compared with the traditional open trench approach. Typically the ‘trenchless’ method will reduce the quantities of incoming and outgoing materials, with a consequent reduction in tipping of spoil and quarrying of imported stone fill. This in turn leads to reduced vehicle movements and subsequently less associated disruption. The table below compares the environmental aspects of open trench and pipe jacked sewer construction at two typical sewer diameters. The comparison assumes that excavated spoil is removed from site to a licensed tip, and that any resultant void after the pipe has been installed is replaced by imported stone backfill overlain by a coated stone surface reinstatement. Since manholes and the delivery of pipeline materials are common to both construction methods, their environmental effects can be ignored. In many cases use of pipe jacking techniques instead of open trenching will contribute positively towards workplace safety, the interface with the general public, and the local and wider environment.