What are the differences between straight microtunnel and curved microtunnel in terms of design and execution?

Q: What are the differences between straight microtunnel and curved microtunnel in terms of design and execution?

In remote-controlled microtunnelling (pipe jacking), a curve layout introduces minimum radius and higher lateral stresses, which increases the geometric control requirements. In design, the curve requires defining radii in plan and/or elevation, verifying the deflection capacity of the pipe-joint system, and recalculating thrust, friction and lubrication due to increased lateral loads. It also conditions the dimensioning and orientation of the attack/reception shafts for assembly, thrust and start-up with correct geometry. In execution, the curved microtunnel requires guiding with progressive corrections, more alignment control and often a more conservative feed to maintain tolerances and protect joints. Straight microtunneling tends to be simpler and more predictable; curved microtunneling provides flexibility to bypass obstacles or reduce intermediate shafts, provided radius, thrust and geotechnical feasibility are validated.

At pipe jacking (microtunneling), the key difference between a layout and a straight and one curved is that the curve introduces minimum radius, higher lateral forces and a superior geometric control requirement. This changes both the design (piping, seals, thrust, lubrication, wells) as well as the execution (guidance and operation).

Differences in DESIGN

Geometry of the layout:
- Straight: simple definition of alignment and slope.
- Curve: it is necessary to define radii (in plan and/or elevation) and tighter tolerances. The minimum radius is usually determined by the system. pipe-joint, (Related to geometrical control in the following areas: lubrication, lubrication and thrust. alignment, curvature and dimension).
Piping and gaskets:
- Straight: standard configurations are normally used.
- Curve: the angular deflection capacity of gaskets, possible pipe lengths shorter or specific solutions to avoid overloading joints and combined stress damage.
Thrust and friction:
- Straight: the thrust is mainly calculated by longitudinal friction and geotechnical conditions.
- Curve: often increase the lateral loads and effective friction, so the design of thrust, overcut and lubrication is adjusted; in certain cases, the use of complementary solutions to keep forces within limits is considered.
Wells (attack/reception) and associated civil works:
- Straight: wells are sized for standard assembly, thrust and logistics.
- Curve: becomes more critical the positioning of the thrust frame, The space for maneuvering and starting with the correct geometry. See how to dimension the attack and reception wells and the support of civil work.
Equipment selection:
- In curve, the capacity of guiding/steering and the fit of the equipment with geotechnical engineering and layout take on even more weight. See choice of tunnel boring machine.

Differences in EXECUTION

Guidance and control:
- Straight: the alignment control is more “stable” and requires fewer corrections.
- Curve: the team must describe the curve with progressive corrections, with more topographic/operational control and, often, a more conservative advance to maintain geometry. (See alignment, curvature and dimension).
Production rate and risks:
- Straight: is usually faster and more predictable.
- Curve: may require more adjustments, with greater sensitivity to deviations, friction management and joint integrity.
Typical curve advantage:
- Allows you to avoid obstacles and, in some cases, reduce intermediate wells or better adapt to urban constraints and easements, especially in the infrastructure crossings.

If you want to see a real example of a microtunnel in curve within the company's references, you can consult Works and the case Microtunnel in Curva Arenao. To define minimum radius, well strategy and thrust limits in your layout, it is most efficient to do it with Technical assistance and engineering.