A swivel is attached to the back reamer, connected to the pipes to be installed, towing to the machine (entry pit) side. Back reaming and pulling the pipes at the same times will allow the pipes to be installed underground without excavation, during this process the drill fluid will assist the lubrication factor and creating a slurried area around the drill hole for the pipe to be installed without any void.
The back reaming and pull back will continue until reamer and pipes reach the launch side of the directional drilling, then disconnect swivel and towing head from the pipes will complete the drilling work.
A surface level is again repeated later six months and one year after the directional drilling job is finished as for the surface settlement limit is not more than 2 mm at period of six months and not more than 5 mm at period of one year.
The formula for maximum surface settlement is : Smax = 0.313 VLD2/i D excavated diameter of bore/tunnel distance form bore/tunnel centerline to point of inflexion of settlement trough Smax maximum settlement with a settlement trough VL volume loss as ratio of notional excavated volume of tunnel