What is the difference between an attack well and a receiving well?

In a work of pipe ramming or microtunneling, the attack shaft is the point from which the excavation is started and the pipes are pushed, whereas the reception shaft is the arrival point of the tunnel boring machine or shield at the end of the section. Both are critical elements of the auxiliary civil works, but have different functions, dimensions and technical requirements.

In the projects of pipe ramming y microtunneling in terrestrial and subway applications, the design of the vertical pits for driving and microtunneling conditions the feasibility, performance, safety and logistics of the entire execution.

Attack well function

The attack shaft houses the main equipment necessary to initiate and execute the advance. From this point the tunnel boring machine or shield is installed, pipes are laid, thrust is transmitted and many of the auxiliary services of the work are managed.

Normally, the attack well should allow:

Install the push frame: structure that transmits the force necessary to drive the pipe and move the TBM forward.

Introduce piping and equipment: sufficient space for lowering pipes, tools, auxiliary conduits, guiding systems and excavation elements.

Manage excavated material: extraction of soil, sludge or debris, depending on the system used, especially in works with EPB tunnel boring machine o hydro shield.

Guarantee access and security: ladders, platforms, ventilation, lighting, pumping, lifting, collective protection and emergency protocols.

Check the initial alignment: the geometry of the shaft must allow the correct orientation of the exit axis, the slope and the microtunnel elevation.

Function of the receiving well

The reception shaft is located at the final end of the section. Its main function is to receive the tunnel boring machine or shield, allow its recovery and facilitate the connection of the pipeline with the projected infrastructure.

The receiving well usually requires less operating space than the attack well, but must be properly designed for:

Receive the tunnel boring machine: have sufficient dimensions for the entry, stop, disassembly or extraction of the equipment.

Control the arrival: ensure that the TBM reaches the intended point within axis, elevation and orientation tolerances.

Allow final connection: facilitate the connection with collectors, chambers, existing networks, outfalls, catchments or other infrastructures.

To guarantee watertightness and safety: especially when there is a high water table, water pressure or connection to networks in service.

Main technical differences

Execution point: the attack well is the origin of the breakthrough; the receiving well is the end point of the section.

Equipment: the attack well concentrates on pusher frame, hydraulics, guidance, feed, extraction and logistics. The receiving well focuses on arrival, equipment retrieval and final connection.

Dimensions: The attack well usually requires more space because of the length of the tubing, the pusher frame, the auxiliary machinery and the lifting maneuvers. The receiving well may be more compact, although it depends on the diameter, depth and recovery method.

Loads and stresses: the attack shaft must resist the driving thrusts and transmit them to the ground or reaction structure. The receiving shaft is more conditioned by the equipment entry, stability, watertightness and final connection.

Logistics: the attack well is usually the operational center of the work; the reception well acts as the exit and connection point.

What conditions the design of both wells

The design of the attack shaft and the reception shaft depends on the diameter of the pipe, length of the section, depth, geology, water table, excavation system, available space, access, traffic, affected services, safety requirements and method of connection with the existing network.

In urban environments, infrastructure crossings, In areas with groundwater or developments with occupancy restrictions, the position and dimensions of the wells may determine whether a trenchless solution is feasible or whether the layout needs to be adjusted.

Minimum checklist to define attack and reception wells: pipe diameter, section length, depth, inlet and outlet elevations, geotechnics, water table, expected thrust, available space, access, excavation method, traffic restrictions, affected utilities and final connection.

Request a technical review for sizing of attack and reception wells in pipe jacking, microtunneling or trenchless technology projects.