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Microtunnelling technology

Application

It is applied for installation of pipes with diameter from ø 250mm to ø 2500mm, when keeping inclination with high precision is necessary. Installation at a curvilinear path is also possible. The technology is similar to the one which is used for the construction of the tunnels of the metro by means of a tunneling shield, but at a reduced scale. 

 

Technology advantages

Keeping the direction and inclination of the drilling with a very high precision

Allows installation of pipes at a curvilinear path

Possibility for direct installation of fiberglass, polymer concrete and steel work pipes.

Suitable pipes

Polymer concrete, fiberglass and steel pipes

 

Technological process:

The microtunnelling machine, consisting of boring head, pushing hydraulic press and laser system for drilling control and guiding is installed in the preliminary built start shaft. The pipe installation is implemented through construction of a tunnel of pipes by means of the microtunnelling machine, as the work process is as follows: 

A hydraulic press in the start shaft pushes forward the boring head, followed by the joining sections of the pipe. The boring head is equipped with a rotary cutting shield, which crushes the soil and forms a tunnel from the start shaft to the reception shaft. The soil is transported through the head and the pipes to the start shaft, from where it is taken to the surface. After the first pipe is installed, the hydraulic press retracts and a new pipe is lowered at the free space. After that the hydraulic press starts pushing again the row of pipes and the boring head. The process is repeated until the boring head reaches the reception shaft. Drilling is facilitated by a drilling fluid, consisting of water solution of bentonite and additives which is fed through nozzles before the cutting shield. The drilling fluid facilitates soil cutting and helps reducing the mechanical friction during drilling, protects the pipe against damages and stabilizes the tunnel. The operator runs the microtunnelling machine by means of a laser guide system. The laser is located in the start shaft and its beam indicates the exact direction which should be followed during the implementation of the drilling. An electronic “target”, installed in the boring head, shows its actual position and the necessity for a correction of the direction. Occurred deviations are corrected by changing the position of the boring head.

 

 

 

Construction of a culvert (ф2400mm) under a ring road in Plovdiv and Sofia-Burgas railway
Microtunnelling for the first time in Bulgaria