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Pipe jacking or micro tunneling is one of the trenchless technology developed to minimize or eliminate the need for surface excavation or reduce environmental damage and associated costs for underground construction such as crossing road or railways, river bed, street building and other pipe-laying engineering.
As the diagram shows that, for most pipe jacking constructions, the Microtunneling Boring Machine (MTBM) and jacking frame are set up in the starting shaft (also called launching pit) at the required depth. The operator is given constant feedback about the machine's location, orientation and devices via a computer console or CCTV camera. Most machines also have video cameras set up to enable the operator to monitor activities in the machine head and other equipment. The operator controls the MTBM and the jacking frame from the central control room (CCR) which is usually situated on the surface, next to the launching pit.
In most microtunneling operations the machine is launched through an entry eye and pipes are pushed behind the machine. This is a process is repeated until the Microtunneling machine reaches the reception shaft (also called reception pit). As the machine advances, more tunnel liner or pipe is pushed from the starting shaft, through the entry eye. Thus, the speed of the advancing machine is controlled by the speed at which the pipe is inserted into the entry eye via the extension of the hydraulic rams in the jacking frame.
During the process of microtunneling, excavated spoil is being taken out either by slurry discharge pipeline (slurry balanced type) or screw and belt conveyor system (earth pressure balanced type)
As the length of tunnel increases, the friction of the ground around the pipe increases as well. Usually, two practices are used to minimize this friction. First, over-cutting is used to give a slight gap between the inner edge of the tunnel and the outer edge of the pipe. Secondly, a lubricant, often bentonite slurry, is injected into this gap.
In addition to the jacking frame, smaller jacks, called "interjack shell", may be inserted between sections of tunnel pipes when the pushing force is not enough. Each interjack shell has its own jacking force. Friction on the pipe sections between the interjack shell and the tunnel entrance helps to prevent the pipe from sliding out backwards. So while the pipes behind the interjack shell does not move, those sections in front of it receive additional pushing force.

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