What Does Pipe Jacking Mean?

Pipe jacking is a non-excavation method of installing pipelines, conduits, and utility corridors by applying forces to push the pipe through the ground while performing controlled excavation at the working face.

The pipe jacking process begins with the excavation of relatively small entry and exit pits at the beginning and end of the pipe installation (usually at the manhole location). These pits are just large enough to accommodate the tunneling equipment and construction personnel. Once the pits are excavated, a hydraulic jacking rig and a mini-tunnel boring machine are put into position.

The hydraulic jacking rig then applies a force that "pushes" the tunnel boring machine through the walls of the entrance pit and into the ground. Once the machine reaches its intended location in the soil, a section of pipe is lowered into the entrance pit behind the jacking rig and mini-tunnel boring machine. An adapter ring is typically used to connect the pipe section to the tunnel boring machine.

Next, the jacking rig again applies a force that forces the pipe and machine forward on their way to the exit pit. This process continues as several pipe sections are jacked up in sequence until the cutter head reaches the exit pit.

 GRP Jacking Pipes (Trenchless)          

Pipe jacking can also be referred to as ramming.

Pipe jacking can be performed on various types of pipe materials, including concrete, clay, and steel with standard diameters ranging from 150 mm to 2,400 mm. While pipe jacking is a versatile trenchless installation process, it is not a one-size-fits-all solution.

To get the most value from the pipe jacking process, several key factors need to be considered, including soil conditions, tunnel length, and pipe diameter.

Soil conditions suitable for pipe jacking

While pipe jacking can be used in a variety of soil conditions, from soft rounds to rock, a detailed site survey is recommended to determine the soil characteristics in the vicinity of the excavation. In general, pipe jacking is well suited for locations where the operator cannot be located inside the machine.

 GRP Pipes            

However, engineers and contractors should be careful when jacking in extremely weak soils, as there may not be sufficient soil strength to support the desired alignment. In such cases, strengthening or stabilization methods, such as ground freezing or grouting, may be required.

Poor ground conditions may also have strengths that are insufficient to provide the necessary response required for jacking. In such cases, piles or other reinforcements may be required to increase the reaction capacity of the thrust wall.

However, these additional measures do add to the total cost of the drive.

Achievable tunnel lengths and pipe diameters

Jacking lengths in excess of 1 km can be achieved using this trenchless technique. The maximum drive length depends mainly on the engineering properties of the surrounding soil and the diameter of the installed pipe. For example, when jacking with smaller diameter cutting heads (less than 30 inches), longer drive lengths may be difficult to achieve because booster pumps and intermediate jacking stations may not be possible due to size constraints.