The first general overhaul after almost 100 years of operation was therefore a top priority for Wacker - and posed enormous challenges for those involved in this major project.

Built between 1915 and 1922, the Alzkanal still supplies electricity, emergency power and cooling water to the main plant of the global chemicals group. To ensure that this remains the case in the future, the 16.7 kilometer long channel was extensively renewed in several sections and the structural substance of eleven structures and two tunnels renovated. Over 400 skilled workers and numerous special equipment were in continuous use to cope with the demanding infrastructure measures. In the course of the rehabilitation of 1.8 kilometres of channels, 0.9 kilometres of tunnels and three canal structures in lots 8-13, the client Wacker commissioned the rehabilitation specialists from Max Bögl in a joint venture.

Repair with state-of-the-art techniques

After preparatory measures had been taken in advance, the canal could be backed up as planned within three days, so that by the end of August 2016 there was "freedom to build" within the channel. In the now completely empty sewer, around 40,000 square metres of concrete were cleaned over the entire length of the stretch using high-pressure rinsing vehicles. After the subsequent inventory and damage survey, partly using the latest laser scanning technology, the rehabilitation work could begin. To this end, the joints, which had become old, were repaired over a total length of around 5,000 metres and sealed with a new grout. Local damage to the trapezoidal channel was repaired as required.

In the area of the structures, the old coating and the damaged concrete also had to be removed using high-pressure water jets or special attachment milling machines. These surfaces were then reprofiled with shotcrete/mortar and provided with a new coating. In addition to the surface repair, a large number of cracks, defects and joints had to be worked on. At peak times, up to 140 skilled workers, accommodated in a residential camp set up especially for the construction project, were employed 24 hours a day, seven days a week in multi-shift operation. The core measures were completed on schedule after a construction period of only seven weeks.

Cavity backfilling with low pressure injection

In the course of the 20th shutdown in the history of the canal, two tunnels, each 206 and 688 metres long, had to be rehabilitated near Burgkirchen. Both tunnels were built in Belgian style at the beginning of the 20th century. Over the decades, however, parts of the wooden formwork remaining in the mountain began to rot behind the tunnel wall. Numerous cavities were created, which now had to be filled. For this purpose, the damaged areas were localised with a georadar and corresponding boreholes were drilled. A cement slurry was then injected into the approximately 5,000 boreholes using a low-pressure injection process, thus permanently filling the cavities. In total, almost 1.6 million litres of cement bentonite suspension had to be injected into both tunnels with several injection pumps running in parallel.