Page 1 Page 2 Page 3 Page 4 Page 5 Page 6 Page 7 Page 8 Page 9 Page 10 Page 11 Page 12 Page 13 Page 14 Page 15 Page 16 Page 17 Page 18 Page 19 Page 20 Page 21 Page 22 Page 23 Page 249 An introduction to pipe jacking and microtunnelling 2 APPLICATIONS AND 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, the incidence of accidents 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. 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, for comparison their environmental effects can be ignored. As a result of the foregoing the carbon impact is significantly reduced, particularly on urban main drainage and flood relief schemes and this can be readily assessed using the carbon calculator on the PJA website. This carbon calculator was developed by the Transport Research Laboratory and verified by the Water Research Centre. In many cases the 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. SAFETY BENEFITS ENVIRONMENTAL BENEFITS 600mm ID pipeline 4m deep, 100m length 1200mm ID pipeline 4m deep, 100m length Aspect Open trench Trenchless Open trench Trenchless Excavated width 1400mm (trench width) 760mm (OD of jacking pipe) 2350mm (trench width) 1450mm (OD of jacking pipe) Reinstatement width 1700mm None 2650mm None Excavated volume per metre of pipeline 6.1m3 0.5m3 10.28m3 1.65m3 Imported stone fill and coated stone per metre of pipeline 11.9 tonnes None 18.27 tonnes None Number of 20 tonne lorry loads per 100m pipeline (muck away and imported stone) 136 8 220 21 Tonnes CO2 emissions 66.7 27.1 110.6 69.7 2a) Comparing the environmental aspects and carbon savings of open trench and pipe jacked sewer construction at two typical sewer diameters