Guidance System SLS-G

The SLS-G Gyro based guidance system uses a self-leveling, north-seeking gyro compass for the determination of the horizontal position and azimuth of the TBM. The calculations of this system are based on the principle of the dead reckoning which means that it is assumed that the TBM will move exactly along the direction which is defined by its axis. The difference between the direction along which the TBM is moving and the axis of the TBM is called the drift. This drift will influence the calculations of the SLS-G. Check measurements for the calibration of the system must therefore be carried out every 40 minutes in order to determine the TBM drift and reduce its influence to a minimum by pre-setting this value for further calculations. The height will be precisely determined by the integrated electronic hose leveling system. When properly handled it is not necessary to do check measurements for the hose level. The accuracy of this system is independent from the driven length. It is the same every time. The horizontal position of the TBM will be updated after each gyro measurement while the vertical position is updated continuously. During the gyro measurements (every 1 min., duration approx. 4 min.) the advance must be stopped.

Guidance System SLS-RV Plus

The operating principle of the software module SLS-RV Plus is more or less identical to the SLS-RV with the difference, that for the precise and refraction-free determination of the height of the TBM an electronic hose leveling system is integrated. A reference module with integrated height sensor will be mounted inside the start shaft. Another height sensor will be mounted inside the tunnel next to the bracket on which the Laser Theodolite is mounted. Both sensors are connected by a hose line which is filled with a special liquid. The height sensors are pressure sensors which are measuring the pressure of the liquid. The different pressures which are indicated at the two sensors are a precise measure for the height difference between the sensors. The integration of the electronic hose leveling system in combination with the SLS-RV is used whenever there are special demands on the precision of the determination of the height or when the principle of the invariance is not given (i.e. buoying of the pipeline).