36 NOVEMBER 2021 WorldWide Drilling Resource® Microtunnelling New Sewer System for Belgium’s Liège Airport Adapted from Information by VMT GmbH Liège Airport, also called Liège-Bierset, is located in the northwest of the city of Liège, in eastern Belgium. It is mainly used for freight operation but also serves more than 23 destinations for passengers. Liège Airport is Belgium’s largest cargo airport and the seventh largest cargo airport in Europe. When a new sewer system was needed, the decision was made to contract with Denys, a specialty contractor with experience in sewer construction, located in Gent, Belgium. The plan was to install over three miles of new sewers underneath the airport complex. Installation of around 3000 feet of 70inch-diameter pipe would be achieved using microtunnelling techniques. Denys engaged experienced microtunnelling contractor KBoringen to complete this part of the project. Microtunnelling works were completed with the contractor’s Herrenknecht microtunnelling machine utilizing a TUnIS Navigation MTGYRO guidance system from VMT, supplier of navigation systems in tunnelling worldwide. This operation was unusual since it was decided not to use a hydrostatic water level (HWL) system in conjunction with the gyro system to establish elevation for the boring machine. Simplifying operations during excavation, this decision is believed to be the first time such a pipe jacking project has been undertaken without the HWL. To maintain the required tolerances and in particular to not create a counter slope, control measurements were planned at intervals of approximately 196 feet, corresponding to a typical control measurement interval when using gyro navigation systems. These measurements were performed by the specialists from VMT, who were on-site during the entire course of the project to optimally support the new generation navigation system. Since the plan was to extend the control measurement intervals above the usual 196 feet, a tunnel laser was installed parallel to the gyro system, which was used to spot-check the determined position. Navigation with gyro compass without hydro level proved itself in the project, with the specified tolerances being adhered to at all times. Given the location of the new sewer under the high-speed double-track railways, the project also utilized a VMT modular system for automated deformation monitoring (MODUS) to monitor deformation of the rails, an application which is unusual for microtunnelling projects where bore diameters are relatively small and ground deformation is usually extremely limited. Commenting on the Liège project for K-Boringen, chief operating officer Wim Feyen said, “Working without the use of the hydrostatic water level simplified the handling of the drive considerably. Due to production requirements, the intervals of our check surveys to monitor the accuracy of the gyro guidance system were a little longer than we would have liked. However, despite this, the alternative calculation method for the vertical position reached the accuracies VMT had stated in advance, and the bore [was] completed within the required tolerances . . . This project has shown us that, with the right equipment and the right backup, we can achieve the necessary accuracy of the drive without a hydrostatic water level.” DIR
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