Kemroc cutter wheel in Bad Cannstatt Rapid helps with long term drainage solutionPublished 24/2, 2020 at 13:27
During excavation of a tunnel on the regional railway line at Bad Cannstatt, Germany, a permanent drainage system had to be installed to protect ‘lenses’ of gypsum located in the clay from the possible ingress of groundwater. For this purpose, seven dam rings were installed as groundwater barriers, with control drainage channels at either side of them. The slots that were required were cut into the injected shotcrete using a Kemroc DMW 130 cutter wheel.
While excavating the railway tunnel at Bad Cannstatt as part of the Stuttgart 21 project, the contractors came across some unexpectedly difficult geological conditions. For about 1,000m of the 3.8km long tunnel, both tunnel tubes had to pass through two anhydrite lenses with a compressive strength of approx. 60 to 90MPa. Anhydrite can swell in contact with groundwater and cause severe long term structural damage to the tunnel. For this reason, protecting vulnerable areas against the ingress of water became a high priority.
The plan was to install seven dam rings (groundwater barriers) and 13 drainage channels to control the flow of water immediately before and after each ring. The installation of each ring required a slot, 600mm deep by 500mm wide, to be cut into the outer tunnel wall which was made of a grade C 35/45 shotcrete with double matting reinforcement type Q257A. Additional slots, 400mm to 600mm deep, were cut on either side of the central slot using a Liebherr R924 T tunnel excavator with a Kemroc DMW 130 cutter wheel.
Using the cutter wheel enabled the work to be carried out with extreme precision and in a cost effective manner. Plant manager, Mr. Peter Göbel, stated: “If we had used a conventional drum cutter, we would have had to excavate more material than necessary. By using the cutter wheel, we have broken out precisely the amount that was required which has major economic benefits since we do not get paid for any additional, unplanned work. In addition, we made savings on the extraction and disposal of excavated material as well as the shotcreting costs. Wear costs for the cutter wheel also acceptable.”