Removing a tunnel step by step

Published 5/10 at 16:17

Experts from Fischer Weilheim GmbH developed a new, economical method for the removal of thick concrete tunnel lining in a tram tunnel in Stuttgart, Germany. To begin with, 1.6m deep concrete walls were reduced by cutting strips using a Kemroc rotary drum cutter. A Kemroc cutter wheel was then used to cut the wall into sections, and, finally, the sections were removed, broken down and processed.

Stuttgart, the capital of the southern German State of Baden-Wurttemberg, is constantly changing its appearance. As a part of the major railway construction project, Stuttgart 21, numerous tunnels have had to be excavated and several existing tunnels modified. This is the case in Schillerstrasse, where the passageway connecting the new Staatsgalerie tram stop and the Klettpassage (Hauptbahnhofstop) is being rebuilt. This involves modifying a 12m stretch of the existing tunnel, with work starting in early summer 2020 when the general contractor, Ed. Züblin AG, commissioned Fischer Weilheim GmbH to carry out the work using usual methods. 

The initial phase saw the gradual removing of the crown of the tunnel and the taking out of the lining at floor level while, at the same time, supporting the opening with the installation of ironwork. The demolition work proceeded by removing material from the top and the bottom of the tunnel which was done using a hydraulic excavator with breaker and shear cutter attachments. Work then progressed to the removal of the wall lining which was made more difficult than usual due to the presence of a bituminous sealing layer and brick work between the concrete lining and the outer soil. According to requirements of the recycling industry, these materials should be separated and sorted before processing or recycling.

Using the standard demolition method with excavator and breaker, it was impossible to avoid the three layers becoming mixed together. To prevent this from happening, the contractor Fischer and the Kemroc agent in Baden-Wurttemberg and Switzerland, Otmar Riester, developed an innovative method of demolishing the tunnel walls in segments. Demolition work was carried out using a rented Liebherr R950 tunnel excavator as the main piece of equipment together with a breaker, a shear cutter and two Kemroc cutting attachments. With these tools, the walls could be divided into single 4m to 6m wide sections which were then torn down and processed.

The first step saw the excavator operator use Kemroc KR 165 rotary drum cutter to grind a 1.5m wide vertical slot into the concrete wall. The wall was then narrowed to a thickness of 1m, which is exactly the cutting depth of a Kemroc DMW 220_1000 cutter wheel. The operator then switches to that tool and cuts through the wall just before ground slot. These two steps are then repeated for cutting horizontal slots dividing the tunnel lining into various segments. The next stage was to use a breaker to weaken the segment at the base of the wall before pulling it down using the excavator bucket which results in the tunnel lining wall falling to the floor. In this position, each layer of soil, bituminous material and soil can be removed separately leaving a solid piece of concrete which can be broken down using a breaker and shear cutter for removal from the job site.

Two months after the job began in June 2020, almost half of the tunnel lining had been removed. Christoph Fischer, fourth generation partner at Fischer Weilheim, is responsible for equipment and special solutions in the family company. He commented; “After a short time, it was clear that this was the most effective and economical method for the demolition and separation of material in the tunnel lining. We doubled the expected production rate compared to the single use of hydraulic hammers since it isn’t so easy to get full productivity from an excavator with breaker in the confined space of a tunnel.” 

According to Christoph Fischer, removing the tunnel lining in segments step by step was crucial to the increased productivity. “Once each segment was torn down to the tunnel base, it was much easier to break them down using the hydraulic breaker. We could also use several construction machines at the same time. Of course, the machinery effort is very high but the saving in time was much more important on this construction site.” Christoph Fischer concluded, “In addition, this is also a step forward in the demand for low emission demolition methods which is required so often these days”.

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