What are the civil works and manhole requirements for a pipe jacking project?

Q: What are the civil works and manhole requirements for a pipe jacking project?

A pipe jacking project requires a shaft that allows mounting the TBM, the thrust bed and pipe logistics, ensuring structural stability, water table control and safe access. The receiving shaft must be sized to recover the TBM and receive the pipeline without compromising the alignment. Both shafts need drainage, ventilation, lighting, working platforms and space for slurry plant, in addition to considering maximum driving lengths, minimum bending radii and environmental easements. The civil works are adapted to the geotechnical, diameter and urban or industrial constraints of the project.

The correct execution of a microtunnel depends to a large extent on the design and construction of the attack and reception wells, as well as the associated civil works. These elements are essential to ensure the safe deployment of the TBM, the thrust of the pipe and the geometric control of the tunnel. Their design must respond to the geotechnics, the available space, the diameter of the conduit and the conditions of the environment.

Eurohinca defines the minimum requirements based on its more than 250 sections executed since 1996.

1. Attack well (jacking well)

The attack shaft is the main element, since it houses the thrust bed, the MTBM, pipe logistics and ancillary equipment. Must comply:

Structural and geometrical requirements

Adequate dimensions for the tunnel boring machine, the pushing system and the pipe maneuvering system.
Bottom level compatible with the alignment and slope tunnel.
Stability against water table and lateral pressures, with solutions such as screens, sheet piles, piles or concrete walls.

Functional requirements

Sufficient access for cranes, piping, sludge plant and debris removal.
Safe platform for shield mounting and head alignment.
Drainage, drainage, drainage, ventilation and lighting systems.

Many examples of these wells can be seen in the land and urban infrastructure works reported in terrestrial and subway applications.

2. Reception well

The exit shaft must allow the recovery of the TBM and receive the pipe without compromising the integrity of the route.

Main requirements

Dimensions to recover the MTBM, shield and pipe train.
Lifting systems and space for safe head removal.
Seepage control by means of screens, waterproofing or pumping.

In sensitive areas or in coastal works, this well is integrated with hydraulic or marine structures, as shown in the projects of submarine outfalls and catchments.

3. Length, alignment and logistics

The wells must be located respecting:

Maximum driving length to avoid overstressing.
Minimum radii of curvature of the system pipe-joint.
Accessible areas for piping, sludge, power and tools.

In curved microtunnels or those with complex geometries, such as the microtunnel in El Arenao curve, The position and orientation of the well are decisive in order to comply with the layout.

4. Mandatory auxiliary services

A pile-driving project requires the availability of:

Sludge and return plant, with tanks, pumps and mixing equipment.
Pusher bedplate with sufficient capacity for the diameter and length of the section.
Systems of safety and HSE, including ventilation, safe access, certified ladders, atmospheric monitoring equipment and rescue plan.
Storage areas for pipe, lubricants, bentonite and consumables.

The article how to choose between microtunneling, HDD and Direct Pipe summarizes the relationship between logistics, construction method and civil works.

5. Additional considerations

Coordination with affected utility owners.
Management of civil works and occupancy permits.
Access planning in urban or industrial areas.
Noise, vibration and schedule constraints.

Civil works requirements may vary depending on the diameter, geotechnics and whether urban, railway, road or hydraulic crossings are involved. The section of works executed shows the diversity of configurations used in the field.