Processing of excavated Tunnel Material to produce Aggregates according to the German Construction Products Directive

Challenge the practice is addressing: Authorities legally classified the excavated material from tunnelling as waste because it came from a construction site. Therefore, the local authority did not allow to discharge the process water of the plant back into the lake. The existing sand and gravel operation had to be expanded by a process water treating plant to process the tunnel material.

Concrete practice to achieve the expected goal: The processing of the tunnel material required that 100% of the process water is recycled. The existing sand gravel plant had to be expanded to include the process water and sludge treatment equipment. To process the material flocculants were added to a lamella clarifier to separate the fine components from the water. As the plant could not process the natural clay as sewage sludge, it had to be conditioned by adding lime and the dewatered in a chamber filter press.

Expected impact/goal of the practice: The aim of the project and the basic idea for its execution was to process all the excavated material produced in the course of tunnel boring into a qualified construction material. As a result, around 700,000 m³ of landfill volume could be saved, which conserved local raw material deposits and allowed the tunnel excavation mass to be recycled on site with the shortest possible transport distance. Additionally, a reduction of fresh water requirements for aggregates production by about 85% have been achieved through water recycling, as well as a reduction of CO2 emissions through the use of rail transport for the end product by choosing a processing location with rail connection.

Who is the target user group of the practice/intervention or implementing the practice/intervention? This practice is for companies in the extractive industry.