Shield machine construction is the most important construction method in tunnel projects such as subways. I believe everyone is no stranger to this. In addition, there is another non-excavation construction method, which is pipe jacking machine construction.

What is pipe jacking construction? What's the difference between it and shield construction?Pipe jacking construction is a method of underground pipeline construction that has developed after shield tunneling. Its greatest advantage is that it can cross roads and various underground pipelines without excavating the surface layer. In simple terms, pipe jacking construction is mainly composed of sections of pipes joined together.

The pipe at the very front can be called the tool pipe. During the construction process, the subsequent pipes to be laid should always follow closely behind the tool pipes. The main principle of this is to utilize the internal supports and main jacks.

Under the thrust of the jack, the tool pipe will first enter the soil layer and dig inward. The excavated soil is then discharged through the nearby soil pump or screw conveyor, and at the same time, it is discharged in the form of slurry through the slurry pump and pipeline.

Let's go back to the tool pipe. At this point, the tool pipe seems to have almost completely advanced into the soil layer. Now we can advance the next section of the pipe. The jack retracted, and another section of pipe was hoisted and pushed forward in the same way.

This process was repeated until all the subsequent pipelines were fully advanced. In the end, the tool pipe will be lifted back to the surface from the receiving well, and the entire pipeline will be laid.

It is worth mentioning that although the entire construction process seems simple, it actually involves multiple system principles internally. For example, hydraulic systems, principles of soil mechanics, air pressure balance, sludge-water balance and soil pressure balance techniques, etc. Here, we mainly talk about soil pressure balance.

It refers to controlling the amount of soil unearthed or the jacking speed of the pipe jacking machine to control the earth pressure value in the sealed soil chamber, so as to keep this earth pressure value balanced with the static earth pressure value ahead, thereby preventing excessive settlement or uplift of the surface. This point is crucial throughout the entire construction process.

Having read this far, have you noticed that the scene of pipe jacking construction is somewhat similar to the horizontal directional drilling we mentioned before?It is also not necessary to dig a large area of the land surface. Just bury the pipe underground and keep digging along the underground until the other end of the pipe extends beyond the surface and connects with the drilling rig, and then return to the underground and drill back in the opposite direction. It wasn't long before an underground pipeline was opened up. Of course, this is only suitable for short-term or small-scale underground excavation.

Since both pipe jacking machines and shield machines belong to large-scale tunnel excavation machinery, what are the differences between them?First of all, the most obvious difference lies in the working principle. Although both are used for tunneling, the shield machine uses a hydraulic system to push the drill bit and then uses pipe splicing to form the tunnel wall. The pipe jacking machine is a construction method that lifts the top of the tunnel by jacking into the frame and then continuously sets up formwork on site.

In addition, the applicable scenarios of the two are also different. Shield machines are suitable for tunnel excavation with larger diameters and harder geological conditions, such as in water conservancy and metro projects. The pipe jacking machine is more suitable for the excavation of small-diameter tunnels with more complex geological conditions, such as water supply and gas pipeline projects.