When construction began in July 2024, it was necessary to excavate trenches for the new sewers, which had to go down to depths of 6m underground in places. Site investigation reports indicated difficult ground conditions were to be expected. Therefor the tender included the removal of an estimated 3,000 to 3,500m³ of rock, with an important condition that the excavation work in close proximity to residential and commercial buildings must be carried out with low noise and vibration.

Impressive performance 

The team of the contractor Peter Gross Bau decided to use a 75t and a 35t crawler excavator. In consultation with Kemroc sales consultant Otmar Riester, they chose to use a Kemroc EK 150 chain cutter (150kW) for the 35t excavator and a EKT 220 (220kW) rotary drum cutter for the larger excavator. Both machines were also equipped with hydraulic quick couplers so that they could switch quickly between milling the rock and excavating the milled material.

The chain cutter attachments have a circumferential cutter chain studded with carbide tipped picks between the two cutter drums. When working, the chain removes the rock that would have been left between the two rotating cutter drums. In solid rock formations, trenches can be excavated to a precisely defined width because there is no need for lateral movement of the drum cutter attachment. 

The 35t excavator with the EK 150 chain cutter was chosen to excavate the rainwater and wastewater trenches because the milled width corresponded exactly to the required width of the trench. The EKT 220 model on the 75t excavator  was used to excavate the large volume of rock in the centre of the site to install the cisterns. Here, the priority was not cutting accuracy, but rather sheer cutting performance.

It's the result that counts

The project manager for the scheme was asked several times about the choice of equipment, because a large 75t excavator is very unusual in urban infrastructure construction projects. However,  in Gärtringen there was a precisely defined deadline of 28 March  2025 for all work in the southern end of the site to be completed to allow for the subsequent stages in the construction process. As difficult ground conditions were expected, it was considered appropriate to have enough production capacity to ensure the deadline would be met. By early December 2024, the project manager believed that the works would be completed to schedule due to the use of the excavators and Kemroc attachments.