Wheels of change

German contractor AVG-Nord went for the use of rotary drum cutters when faced with the challenge of demolishing a World War II bunker on Hamburg’s Wielandstraße, with the company being contracted to remove the bunker’s ceiling, two walls and parts of the remaining two walls, With dimensions of 48 x 28 x 22 m (157 x 92 x 72 ft), the bunker was one of the largest of its kind and offered shelter to more than 2,000 people at a time during the war.

The first factor complicating the demolition was the physical nature of the structure, which featured a 3.5 m (11.5 ft) thick roof and walls of the same dimensions, which given the bunker’s nature also were very heavily reinforced with steel rebar. In addition, the bunker’s close proximity to other structures required that the demolition had no physical impact in terms of damage caused to these. Finally, very strict noise and vibration limits were in force for any work in the area, meaning careful selection of the demolition methodology was required.

AVG-Nord used two Erkat ER 1500 rotary drum cutters with each mounted on a 32 tonne carrier. Demolition started with the removal of the roof and then worked down the inside of the building. AVG did not remove the entire wall but left a thin section on the outside edge, removed at the end of the project, that helped to minimise external noise levels as well as retaining dust and debris that might have escaped from the interior.

Despite the presence of a substantial amount of rebar, some of it with diameter up to 20 mm (3/4 inch), the drum cutters worked their way through the concrete with each achieving an average production rate of between 5 to 6 cubic metres per hour (177 to 275 cubic feet per hour). Despite the heavy reinforcement, average pick consumption was less than half a pick for each cubic meter (measured in situ) of concrete cut. With minimal machine downtime causing delays, AVG began in May 2014 and completed the project on time in December with minimum disturbance to neighbours.