Microtunneling is a trenchless construction method in which a borehole is excavated and pipes laid simultaneously using remote guidance, pipe jacking, and continuous support. The microtunneling boring machine (MTBM) is operated from a control panel, normally located on the surface. Personnel entry is not required for routine operations.
Basically, microtunneling is remote pipe jacking. However, due to its cost, microtunneling is usually reserved for pipes that need a high degree of precision over a long distance. Water jetting is used for the cutting head during the boring stage, or an asymmetrical or slanted head and is directed using laser guidance. Only pipes with a circular cross-section can be used because of the boring process.
Trenchlesspedia Explains Microtunneling
Microtunneling is a trenchless construction method that uses a microtunnel boring machine (MTBM) mounted on a jacking frame which is moved forward using jacks. The automatic steering system enables pipes of diameters ranging from 48 inches to 12 feet to be installed accurately.
The automated steering system used for guiding the MTBM during the boring procedure gives very accurate results for curved and long-distance drives. The system utilizes advanced technology such as laser guidance, gyroscope, tachymetry, and closed-circuit television (CCTV) cameras that help the operator to remotely guide the MTBM. The position is relayed constantly allowing operators to guide the MTBM precisely.
Microtunnelling Guidance System
A laser-controlled guidance system is commonly used for microtunneling projects and provides real-time data to the operator for controlled steering operations.
The motorized laser target unit helps determine the horizontal and vertical position and the pitch and roll of the MTBM. While a standard laser sight can keep the machine on course in a straight drive, curved drives require guidance systems such as those used on longer bores. Curved alignments also help extend the drive length by avoiding obstacles and intermediate shafts.
Microtunneling has successfully completed horizontal as well as vertical curves. Horizontal curves allow pipeline projects to follow curved public rights-of-way without too many manholes, and short straight segments.
Correct Use of Guidance System
The guidance system including the camera is thoroughly checked, calibrated and set-up before launch as the guidance system camera is the primary reference for the MTBM operator. The target location is checked at the back end of the MTBM and the line and grade of the alignment are ascertained. The inclinometers and roll sensors are checked to confirm they are functioning well, and then calibrated. The theodolite is also checked for tilt offset and collimation, and the same is also done during the operation if the MTBM experiences a strong vibration, bump, or disturbance.