Unusual application for Kemroc cutter wheelPublished 10/10 at 15:49
Demolition of the Düte Bridge was made more difficult for demolition specialists, UPEK GmbH, due to the very unusual method used to construct the bridge.
Built in 1968, the four lane motorway bridge on the A1 near Osnabrück, had eight pairs of supports holding up a single slab of concrete which was 280m long and 3m wide, made originally from one long, continuous pour. For this reason, the principal contractor for demolition, groundworks and construction, PORR Deutschland GmbH, had to build a steel structure to support the old bridge before it could start cutting into the concrete deck.
The intention was to cut the deck longitudinally into two halves so that one half could be removed and replaced with a new section, before the second half was removed, and construction of the second half of the new bridge could be completed. Passing under the old 300m long and 18m high bridge is not only the river Düte, but also a high speed railway line, so certain demolition works could only be completed during operational breaks in the railway schedule. The countryside near the bridge is also part of a nature reserve, meaning that the use of a long reach excavator to demolish the bridge from ground level was also not possible.
The subcontractor, UPEK from Steinfeld (Lower Saxony), was responsible for the demolition of the eastern half of the bridge over the high speed railway line. The company chose to use a Kemroc cutter wheel Erwetor DMW 220 mounted on a 50t excavator for the delicate demolition work. The procedure was to locate the excavator on the 15m wide half of the bridge deck to be demolished, and to cut out segments of the deck approximately 1m2 in size. After each segment was cut, the excavator bucket was used to pull the segment backwards onto the uncut bridge deck, where it was reduced in size using a breaker or a shearer. As the concrete segment was supported on the bridge deck rather than being suspended in the air, the blow energy of the breaker was very effective in breaking the segments down into smaller pieces. Reducing using shearers was also very effective since the steel reinforcement had been cut by the wheel.
By the end of May 2018, demolition of the bridge section that passed over the high speed railway line was completed, and demolition of the superstructure using conventional methods had started. However, it was also planned to use the excavator with the Erwetor cutter wheel to demolish the remaining 1,150mm thick bridge heads and abutments. In his interim report, the general manager, Mr Johannes Prues commented, “While cutting the 650mm thick concrete road we achieved a cutting speed of 30 meters per hour which translated into one meter of road demolished per hour. Naturally, tool wear while cutting the heavily re-enforced concrete with contained 32mm diameter tension bars, was enormous. However, we achieved the desired production rate for the difficult task in the very short time frame available due to the high speed railway operating times.”
For the demolition of the bridge heads and 800-1,200mm abutments, using the Kemroc cutter wheels had some very important benefits. “The ability of the wheel to cut down to 1m depths made the demolition of some structures much easier than would have been possible with traditional cutting and sawing techniques. In addition, using the cutter wheel on the bridge heads and abutments solved another problem. These structures were also formed from a single pour of concrete, and it was only the cutter wheel that made it possible to demolish the eastern half of the bridge without damaging the western half which remained operational. This would have been very difficult using hammers and shearers.”