Dismantling a bridge using a large excavator and a Kemroc cutter wheelPublished 8/7 at 17:42
Based in southern Germany, demolition company Max Wild is involved in the demolition of the old Saar Bridge at the Saarlouis autobahn. The plan for demolishing the bridge consisted of breaking it down into sections that could be placed on pontoons and floated to a crushing facility on the riverbank. In order to disconnect the lateral cantilever arms and the concrete slab between the two hollow boxes, the company used one of their 40t excavators with a Kemroc cutter wheel attachment.
Demolition of the old bridge started after the four lanes of the new replacement bridge were completely opened in November 2020. The client, the western subsidiary of Autobahn GmbH, awarded the contract for the overall project to the consortium Schnorpfeil / SEH. The consortium sub contracted the difficult demolition work of the old concrete bridge to demolition specialists, Max Wild GmbH which is headquartered in Berkheim in Upper Swabia, operating from several locations all over southern Germany.
The company has a comprehensive fleet of modern machinery and has extensive experience in the demolition of buildings, industrial complexes and bridges. However, even for such a large company, demolition projects like the Saar Bridge do not come along every day. Naturally, motorway bridges spanning large rivers cannot be demolished from the ground. The first stage in the detailed plan for the demolition process involved lightening the hollow box section concrete beams spanning the bridge in both directions by removing all structurally non-essential items from the bridge deck. Once this was complete, the main structural components of the bridge could be lowered onto floating pontoons that would transport them to a crushing facility on the riverbank.
Cutting prestressed concrete
Structurally non-essential items on the bridge were removed following discussions with Kemroc’s application consultant, Marco Schön, using a DMW 220/1000/130 cutter wheel excavator attachment. This has 220kW rated power, with a cutting depth of between 500mm to 1,000mm and a cutting width of 130mm, and was mounted on one of the company’s 40t excavators. Mounted on the arms of hydraulic excavators, the DMW range of cutter wheel attachments are designed for tough applications. Equipped with two lateral hydraulic motors, they develop extremely high cutting forces which produce high production levels. They can even be used to cut through rock with a uniaxial compressive strength of 120MPa or through heavily reinforced concrete.
The attachment encountered heavy resistance on the bridge panel which crossed the Saar River, before two pontoons with a special framework had been located under the bridge panel in order to support the two hollow box elements and float them out later. In order to reduce the weight of the span being carried by the pontoons, the cantilever arms on both were removed as well as the concrete slab located between the two hollow box sections. Under normal circumstances, Max Wild specialists would have cut these structures into sections using a concrete saw, but due to the extremely angled nature of the whole construction the saw would have had to be reset numerous times. In addition, cutting depths as much as 650mm would have been necessary. This led to Max Fus, the site manager, and his team, deciding to make only the longitudinal cuts along the bridge axis with a concrete saw and use the Kemroc cutter wheel for the crosscuts. The concrete was cut into segments, each weighing between 6t and 10t. Each segment was lifted out with a crane and transported to a crushing plant on the riverbank.
The cutter wheel was used in weeks 6 and 7 of 2021. Work was protected by scaffolding suspended over the Saar River. The cutter wheel achieved a surprisingly fast cutting rate according to Max Fus. “The bridge was tensioned in a transverse direction and it was therefore structurally difficult to cut through. Nevertheless, I was surprised that the cutter wheel did not appear to perform differently when it was cutting through prestressed or non-stressed concrete. Working with a combination of diamond saw technology and the cutter wheel, we made relatively quick progress and achieved cutting speeds of around ten linear meters per hour. Even with the relatively high rate of wear on the tungsten carbide tipped consumables, this method has been proven to be the most economical solution due to the high production rates.”