Microtunneling is a trenchless construction technique used to construct small- to medium-sized tunnels. During the microtunneling process, a remote-controlled, laser-guided cutting head drills through the soil while being advanced by a pipe jacking rig.
Segments of the pipe are then lowered into an entrance pit and jacked in sequence until the cutting head reaches the exit pit.
While slurry microtunneling can be used on numerous projects, it is not a one size fits all solution. Several factors must be taken into consideration to ensure that this technique is suitable for a given trenchless project.
Here are some of the questions you should ask to determine if slurry microtunneling is right for your project.
What Are the Ground Conditions?
Slurry microtunneling is suitable for a wide array of soil conditions ranging from soft ground to rock. However, this method is ideal for saturated, flowing, and pressurized soils. Microtunneling is also typically used in ground conditions below the water table, where having personnel in the machine is not permitted.
Caution must be exercised, however, when microtunneling in extremely soft or weak soils, since there may not be enough strength to support the alignment. In this case, ground stabilization methods, such as ground freezing or pressure grounding may be required.
What Is the Required Tunnel Diameter?
Typical microtunneling diameters range from 30-94 in. (760-2400 mm). While smaller and larger diameters can be achieved, it is mainly dependent on the properties of the surrounding soil.
What Is the Maximum Drive Length?
The maximum drive length that can be achieved by slurry microtunneling is contingent on the first two questions. Typical long-drive lengths can reach up to 1000 ft.. This length, however, can be difficult to attain with smaller diameter cutting heads (24 to 30 in.) since vital accessories, such as booster pumps and intermediate jacking stations, cannot be added due to size limitations.
What Accuracy Is Needed?
Microtunneling is ideal for projects, such as gravity flow systems, where a high level of accuracy is needed. Integrated laser guidance systems with simultaneous feedback allow operators to make precise adjustments during tunneling.
Since microtunneling can be more expensive than other trenchless methods, it may not be appropriate in applications where accuracy is not a top priority.