The 600m Trimberg Tunnel is just one of numerous construction projects that were required when building the new A44 autobahn. After breaking through in each of the twin tunnels, work commenced on the interior lining and supporting the steep, shotcreted portal walls with a cladding. Strabag was subcontracted to clad both portal walls, each about 500m long and up to 10m high with blocks of Jurassic limestone. Each of the 900mm x 1,800mm long and 500mm x 900mm high limestone blocks were delivered to site by truck and then trimmed to precisely the correct length. This was the only way that the contractor could meet the joint dimensions specified.

When work began on the east portal of the tunnel in April 2021, a rotary drum cutter mounted on a wheeled excavator was used to trim individual limestone blocks to size. Shortly afterwards, Enrico Trender, the application consultant from Kemroc, visited the site. He suggested doing a trial to compare the performance of an ES 60 HD with a drum and rotation unit with the current attachment. Strabag agreed to the trial, with both the excavator operator and his foreman, Simon Cox, being impressed with the speed and precision of the new attachment.

Fast and Accurate

The ES range of universal cutter attachments were designed for use on excavators with operating weights from 1t to 40t. When fitted with a cutter wheel, they can be used as slot cutting attachments for concrete, asphalt or rock; when fitted with a cutter drum they can be used to accurately profile horizontal and vertical surfaces. For the Trimberg Tunnel, Enrico Trender suggested the ES 60 HD as based on his years of experience, he knew that according to the weight and hydraulic power of the Liebherr A920 wheeled excavator, this model together with the optional rotation module would provide the optimum performance. Based on the successful results of the trial, the Strabag site manager, Andre Hatwig, rented the equipment.

The 9,000 blocks had to be sized before they could be used at the portals of the Trimberg Tunnel. The sizing process in detail consisted of placing the block with one end up against other blocks with wooden wedges underneath so that the face to be milled was facing up at an angle. A petrol powered cut off grinder was then used to cut the outline of the required surface to size so that the finished product would have sharp, straight edges. Using a full hydraulic quick coupler, the operator was able to change over to a universal cutter and milled the front face of the block in a vertical cutting motion up and down the face. After another change – to a grapple as was used originally - the block is transported and placed in position on the portal wall.

By the end of May, at the eastern portal, where the limestone clad wall reached almost 8.5m in height, about half the wall had been completed. According to Andre Hatwig, the Kemroc attachment proved to be a flexible pacemaker for the entire process. He explained, “According to the excavator operator, working with the Kemroc universal cutter was more accurate, faster and quieter than with the standard drum cutter being used previously. Enrico Trender from Kemroc, brought the ideal excavator attachment combination on site and set the hydraulics on the wheeled excavator to the correct values. Now the operator saves an enormous amount of time and fuel while trimming these blocks.” Meanwhile, another Kemroc ES 60 HD universal cutter has been delivered to the western portal of the tunnel to do the same job.