Dry method (not involving any liquid fillers, such as bentonite etc.) is used for pipe-jacking, controllable in terms of its plan and profile, and no soil is carried away from the working passage.
Soil categories: all types of soils except for rocks.
Pipe-jacking works can be carried out from one pit to another (using UNB-20, MNB-50, MNB-125) or, if necessary due to especially confined space, from the well or the OR-1.5 formwork (or MNB-50).
1. Pilot borehole
Preparation: prepare the working pit and the receiving pit; mount the MNB equipment in the working pit; connect the hydraulic hoses to the hydraulic power unit.
The hydraulic power unit generates pressure; the set of hoses is used to transmit this pressure to the jacking unit (the working cylinder). The bar is pressed in. Then, the second bar is screwed on and pressed into soil. While bars are pressed in, an operator uses the radar set to monitor the drill movement direction.
If the drill deviation exceeds permissible tolerances, the drilling direction is adjusted to ensure proper position of the drill tip in soil, both horizontally and vertically.
Note: the drill movement direction is set due to the drill tip special design and alternating translational and rotational motions.
The drilling process, with the radar set continuously used to monitor the exact position of the drill tip in soil, is terminated when the drill enters the working pit in accordance with the design parameters.
2. Expanding drilling
When the drill enters the working pit, it must be taken off and set on the first bar in the expander.
In the working pit, retracted bars are removed.
Then, the expander retraction is repeated.
When the expander enters the working pit, the expander is replaced by that with the larger diameter.
The process of retraction followed by the expander replacement by that with the larger diameter is repeated until the drilling diameter becomes greater than the pulled pipe diameter.
Note: the passage expansion does not involve soil pressing-out (due to soil compaction).
3. Polyethylene pipe pulling into the borehole
The polyethylene pipe is welded (the resistance butt welding method is used), and the gripper is put on the pipe. The gripper is linked with the unit’s expander and bars. The polyethylene pipe is pulled into the borehole until it leaves it and enters the working pit.