The intermediate push stations are required in a pipe jacking when the expected thrust may exceed the allowable capacity of the main frame, the pipe or the soil-pipe assembly. Their function is to distribute the thrust at various points of the section, reduce longitudinal loads, control friction and improve the safety of execution.
In projects of pipe ramming y microtunneling in terrestrial and subway applications, This requirement is studied before the construction site by calculating the expected and admissible thrusts.
When they may be necessary
Intermediate stations are usually valued in these cases:
- High pile-driving lengths, by accumulation of friction between the pipe and the ground.
- Large diameters or heavy pipes, which increase the efforts of advancement.
- Terrain with high friction, such as sticky clays, dense sands, gravels, fractured rock or mixed soils.
- Important depths or coverages, where the earth pressure on the pipe increases.
- Plotting with curves, because they can increase lateral contacts and local efforts.
- Pipe strength limitation, joints or thrust system.
- Attack pit restrictions, The main frame or reaction structure.
The design of the vertical pits for driving and microtunneling also has an influence, because the shaft must allow the thrust system to be installed, withstand reactions and operate safely.
What data are analyzed to decide
To assess whether intermediate stations are needed, they are reviewed:
- Total driving length.
- Outside diameter and material of the pipe.
- Permissible driving thrust.
- Expected ground-pipeline friction.
- Geotechnics and water table.
- Depth and coverage.
- Radius of curvature.
- Lubrication system.
- Type of tunnel boring machine and guidance system.
- Main frame capacity.
- Design of the attack well.
The choice of tunnel boring machine, The final driving effort is also influenced by lubrication and management of the excavated material.
What risks to avoid foreseeing them
Providing for intermediate stations when the project requires them helps to avoid excessive thrust, damage to pipes or joints, stoppages due to lack of feed capacity, deviations, additional wear and tear on equipment, cost overruns and time extensions.
On the other hand, if they are incorporated from the design phase, they allow better planning of equipment, pipelines, wells, supply, progress sequence and costs.
Minimum checklist to evaluate intermediate stations: drive length, outside diameter, pipe material, allowable thrust, expected friction, geotechnics, water table, depth, bend radius, lubrication, frame capacity, manhole design and execution tolerances.
Request a technical review of thrusts and intermediate stations for pipe driving before closing the design or preparing the bid.
ES 
EN 
FR 