Pipe jacking (PJ) and utility tunneling (UT) are trenchless construction methods which require workers inside the jacking pipe or tunnel. The tunnel is generally started from an entry pit. The excavation can be done manually or by using machines. However, it is accomplished with workers inside the pipe or tunnel. The excavation method varies from the very basic process of workers digging the face with pick and shovel to the use of highly sophisticated tunnel boring machines (TBM). Since the method requires personnel working inside the tunnel, the method is limited to personnel entry size tunnels. Hence the minimum tunnel diameter recommended by this method is 42 in. (1,075 mm) outside diameter. Even though it is theoretically possible for a person to enter a 36-in. (900 – mm) diameter tunnel, it is practically very difficult for the person to work in it.
Irrespective of the method, the excavation is generally accomplished inside an articulated shield which is designed to provide a safe working environment for the people working inside and to allow the bore to remain open for the pipe to be jacked in place or the tunnel lining to be constructed. The shield is guidable to some extent with individually controlled hydraulic jack.