What should we pay attention to during the entire pipe jacking construction process?

Compressed air consumption changes continuously during the entire pipe jacking construction process. On the one hand, it is determined by the foundation itself, and on the other hand, it is also determined by the pipe jacking technology. The extremes in the range of variations in foundation and pipe jacking technology combined may result in a wide range of fluctuations in air consumption. Therefore, the calculation of air consumption must be based on this range, taking into account both the upper limit and the lower limit. Specifically, total compressed air consumption consists of the following components:

1. Consumption of the front wall of the work

2. Air loss in the blade foot or shield and in the jacking pipeline

3. Loss at the pipe outlet in the jacking pit

4. Losses in the jacking pit

5. Losses on the sealing devices of personnel lock chambers and material lock chambers

6. Losses in compressed air piping together with all moldings and pipe fittings

7. Losses in air compression equipment

8. Loss of entry through the personnel lock room

The fundamental reason for ground deformation during pipe jacking construction is the disturbance of surrounding soil caused by pipe jacking construction. Ground deformation consists of the following five parts:

(1) Ground deformation before the tunnel boring machine arrives

When the tunnel boring machine is far away from the measuring point, the soil will be disturbed due to the cutting, mixing and vibration of the cutterhead. There are pores between soil particles (the pores contain water and air). Under the action of disturbance, the water and gas in the pores are discharged, the soil particles move relative to each other, the soil produces a certain amount of compression, and slight settlement occurs on the ground.

(2) Ground deformation when the tunnel boring machine arrives

When the tunnel boring machine is very close, the soil located directly in front of the tunnel boring machine is squeezed by the thrust of the jack, the cutting shear force of the cutterhead, and the vibration load, and the stress state is very complex.

(3) Ground deformation when tunnel boring machine passes

When the tunnel boring machine passes, a shear sliding surface will be formed between the tunnel boring machine shell and the soil layer. Shear stress will be generated in the soil layer near the shear sliding surface, and the shear stress will cause ground deformation. The faster the advancement speed, the greater the shear stress and the greater the displacement of the surrounding soil.