Pipe Jacking is a trenchless technology method for the installation of a prefabricated pipe through the ground from a drive shaft to a reception shaft. It is a technique used for installing pipes under the ground using a tunnel boring machine and hydraulic jacks located inside a jacking pit. A shield is inserted into the ground through a drive shaft or reception point and cuts a bore. As the shield advances forward, excavating the earth in its path, sections of pipe are jacked into place directly behind it using powerful hydraulic jacks.
The technique is a widely employed alternative to open-cut excavation and existed as a means for crossing under roads, railways, rivers, canals, buildings, airfields and other projects with the goal of minimizing or attempting to avoid disruption of traffic altogether.
The pipe jacking process begins first by constructing a drive shaft or pit at the face and a thrust or reception shaft or pit at the corresponding end of the pipeline. These pits will vary in size based on the excavation method deployed in the pipe jacking process.
The tunnel or jacking shield is then launched inside the launch shaft. A thrust wall is constructed to provide force against which to jack pipes into place behind the jacking shield. To ensure the jacking force os distributed equally through the entire diameter of the jacked pipe, a thrust ring is also used to transfer loads. Jacks are interconnected hydraulically to ensure that the thrust from each pipe is consistent. The amount of jacks needed to install the pipes is dependent upon the size and length of the pipe being installed, the strength of the jacking pipes, and how much frictional resistance is required.
As the pipes are jacked into place, the correct alignment of the pipeline is consistently checked. Accurate pipe alignment can be checked and carried out with the use of a steerable shield and by placing guide rails inside the thrust pit upon which the pipes are laid. Traditional surveying equipment is normally use to carry out checks for shorter pipelines. The shield is then removed from the reception pit once jacking is completed and the pipeline is installed.
To minimize the likelihood of the occurrence of ground settlement, various ground treatment works can be employed, including jet grouting, silica/cement grouting, dewatering, and ground freezing.