Monday, July 15, 2024

Trenchless in a world heritage site

Bodenbender - Resins for the special requirements of sewer rehabilitation

Covering an area of 2.4km2, Bergpark Wilhelmshöhe in Kassel (Germany) is the largest mountain park in Europe. In 2013, the park was declared a UNESCO World Heritage Site and the German National Tourist Board ranks it among the top 100 sights in Germany. Its famous water features including Wilhelmshöhe Palace, the Hercules statue and Kassel’s landmark, play a big part in attracting over 750,000 visitors a year.

There are 14 historic buildings in the lower Bergpark between the entrance and the castle plateau, some of which are now used for catering. All of the wastewater pipes and sewers here will be renovated in accordance with current regulations. This involves a total of around 1,200m of rainwater, wastewater and mixed water pipes with nominal diameters from DN 100 to DN 150 and around 2,650m of pipes from DN 100 to DN 600.

The project team

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The owner is the state of Hesse; the Museumslandschaft Hessen Kassel MHK acts as its representative and user. The client is the northern branch of the Landesbetrieb Bau und Immobilien Hessen (LBIH) in Kassel. Construction supervision is the responsibility of AGC – Aqua Geo Consult GmbH, Kassel; Hermanns HTI-Bau GmbH & Co KG, Kassel, is responsible for construction. The upgrading, renewal and renovation of the historical sewers, some of which are up to 250 years old and have a box section, is being carried out by Hermanns itself; Swietelsky-Faber Kanalsanierung GmbH, Blomberg, has been commissioned with the sections to be renovated without trenches. Hoses and resins were supplied by Bodenbender GmbH from Biedenkopf.

In order to protect the vegetation, especially the trees, some of which are centuries old, and not to disturb the visitors, the client and users set strict guidelines. These included as much trenchless refurbishment as possible and carrying out the construction work during the winter months when there are less visitors.

History: A refugee founds the Kassel canal network

Construction of Bergpark began in 1680: Landgrave Karl and his successors had a Baroque park laid out that was unique in a European garden design – Italian terraced gardens were smaller, French Baroque parks extended across the plain. Today’s design is based on English landscape parks, especially in the lower area.

In “Cassel”, as the town was called until 1927, underground drainage channels leading into the low-lying Fulda existed centuries ago. The canals, which were made of quarry stone and often only covered with slabs or completely unlined, were not connected.

Around the turn of the 18th century, the Huguenot master builder and engineer Paul du Ry (1640-1714), who had fled France, developed an interconnected sewer system for the Huguenot settlement in the Oberneustadt. He was also involved in the construction of the cascades in the new Bergpark.

Du Ry had previously acquired extensive knowledge of hydraulic engineering in Maastricht in the Netherlands. This was one of the reasons why Landgrave Charles, a devout Calvinist and one of the first to offer asylum to persecuted French Protestants, brought him to Kassel.

Some areas of the Bergpark were already canalised during construction, primarily for surface water. The entire canalisation took place from the beginning of the 20th century. This means that some of the canals that are not considered to be from the time of construction. These are now being renovated without trenches and are more than 100-year-old – “antiques” from before the First World War.

Bernd Schäfer, deputy manager of the Swietelsky Faber branch in Blomberg and the project manager, is delighted to be working on the landmark in his home town: “We’ve refurbished pretty much everything from airports to hospitals – but we haven’t yet worked on a World Heritage Site.”

Economic miracle without monument protection: patched up with mortar & co.

The camera inspections at the start of the project delivered some surprises: Some of the old plans were very accurate and only required a few corrections. Other pipes took detours that are no longer comprehensible today or deviated greatly from the old documentation or assumed routes.

The damage analysis for the implementation planning confirmed previous expectations: In leaking pipes, the lush vegetation had caused severe damage due to root ingrowth. The old joints were also no longer “sewage-proof”.

In addition, the renovators came across sections of pipe that had been “repaired” with mortar and the like in the 1950s and 60s without regard for the protection of historical monuments, but in an economically miraculous manner.

Where possible, historical renovation is now being carried out. The old sewer sections are still being used for surface water and supplemented with an additional pipe. For around 1,000m it was possible to dispense with replacing the pipes using the open trench method and to carry out trenchless renovation with pipe liners.

Bodenbender: Resins for the special requirements of sewer rehabilitation

Swietelsky-Faber utilised products from Bodenbender GmbH in Biedenkopf, Hesse, for the refurbishment: “We know the material, we know how it reacts at different temperatures – and if there are any difficulties, we can be sure that our partner will be on site immediately – even providing an alternative product if required.” Swietelsky-Faber has been working with Bodenbender for around 20 years: “We have always found Bodenbender to be extremely reliable and flexible,” says Schäfer.

Bodenbender is one of the pioneers in house connection rehabilitation with pipe liners. Originally a pipe and sewer cleaner itself, the company developed its own resins and liners together with Bayer AG in the early 1990s. The aim was to develop a resin for the special requirements of sewer rehabilitation. It had to adhere perfectly to various substrates, harden quickly and “spill-free” for immediate milling and be easy to process even with large temperature differences. Above all, it should be possible to correct errors so that the material does not have to be milled out if the inliner bulges after curing.

In 1991, the Point-Liner® was launched; this was followed in 1994 by the PL® Point-Liner system, which was supplied as a perfect fit; other products followed. Today, Bodenbender is active throughout Europe and Australia. The company also offers its customers and users comprehensive training at its in-house academy and on site. “We not only understand our customers’ business, we also master it ourselves,” says Jonas Bodenbender, Technical Director of the company.

The right liners and resins for every challenge

Bodenbender offers precisely tailored quantities and mixtures, but from here the customer takes over: “We first measure the pipe liners directly on site and adjust the resin accordingly,” explains Schäfer. This means that a product with a short curing time can be used for short pipe liners. For long liners, a longer pot life helps to work carefully and accurately. In Kassel, 1m to 50m long liners made of needle felt or polyester were used, depending on the condition, location, nominal width, dimensional jumps and bends of the sewer.

“We also coped well with special challenges such as jumps in nominal width, the wrinkle-free adaptation of the inliners to the old pipes, difficult bends, and the transitions of the pipes into the sections,” says Schäfer: “However, there is another reason why the work is going even better than planned, the mild winter with low temperature differences has actually made it easier for us.”

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