Pipe jacking is a tunneling technique used for underground pipeline installation which causes minimal disruption on the surface. The technique is now widely used for a variety of purposes like sewer relining and replacing, laying oil, gas or water pipelines, and also for telecommunication and electrical installations.
In pipe jacking, a line of pipes is driven inside the ground using hydraulic jacks from a jacking pit pre-prepared for the purpose. As the jacking pit pushes the pipeline out, a shield in front of it carries out the excavation. The process is repeated to push the pipeline further ahead. Depending on the exact conditions, excavation is done both manually and with tunneling machines. Nowadays, it’s possible to perform pipe jacking with remote controlled tunneling equipment, which can be steered and operated from the surface. The process of remote controlled excavation and piping is also known as Microtunneling. Normally this method is used for pipelines with a diameter of less than 900mm, but it can also be used for larger diameters.
Around 40 years ago, when pipe jacking in the United Kingdom was only in its infancy, tunnels were manually excavated for pipeline installation and pipes were jacked with basic tools like spacers and hydraulic jacks. This was primarily used for pushing the pipeline through under existing structures and the technique was very crude. Naturally the installed pipes were often damaged and often times their level and line were not up to the acceptable tolerance limits.
This problem was wonderfully solved with the introduction of modern mechanized tunneling systems capable of efficiently performing pipe jacking in different types of ground conditions. Actually, these tunneling systems can be custom designed for specific underground requirements, and have been a tremendous benefit to the society.
Environmental issues are now affecting both power and control in economic and technological developments, and as a result, the hi-tech excavating machines now use a slurry tunneling technique, mixing the cut spoil with slurry and then pumping it out to a cleaning plant on the surface.
In more than 95% of UK tunneling projects, the machine exaction process is used. This is also the best technique for excavating water-bearing soil, because it prevents groundwater inflow and thus reduces the risk of the tunnel being flooded. A carbon calculator is being developed by the Pipe Jacking Association of U.K. for immediate assessment of greenhouse gas emission levels during a Microtunneling process compared to the old school open-cut pipe jacking technique.
In the development of modern tunneling and pipe jacking technology, academic research has played a significant role. It has more clearly defined the relationship between different ground conditions and friction load, the relationship between different types of packing materials and their load and deflection properties, the effects of cyclic loading and the use of lubricants, and site investigation test development for better prediction of frictional forces. The complex relationship between different ground conditions, machinery and pipes is now better understood, and the new generation pipe jacking and tunneling equipment is certainly a true reflections of that.