Germany has far too little landfill capacity in relation to the volumes of waste expected in the future. New landfill sites are also rare. Especially as new construction takes a long time because, among other things, the approval processes are lengthy and the requirements are high. The solution: In order to guarantee disposal safety, the available capacities should be used as effectively as possible. This is made possible by maximum compaction. This is made possible by innovative compaction methods, which the geotechnical engineering team at HTWK Leipzig has tested together with AGR Abfallentsorgungs-Gesellschaft Ruhrgebiet mbH at the Datteln central landfill site in North Rhine-Westphalia.



Soil-like waste that can no longer be used anywhere due to pollutant contamination or a lack of recycling routes is often deposited in landfills of classes DK-I and DK-II, such as the Datteln central landfill. Such mineral construction waste, including excavated soil - i.e. soil and stone - was once again the largest waste group in Germany in 2021, at around 221 million tons. As the last storage locations, they push landfills to their capacity limits.



Civil engineering compaction methods applied to waste disposal



As the capacity limit for DK-I waste at the Datteln central landfill had almost been reached, the remaining volumes were to be reused as far as technically possible. To this end, the waste already deposited in the landfill was compacted using impulse compaction in order to create more space and thus new landfill space.



"In the field of research, we have been working on dynamic soil compaction for many years. Together with the landfill management of AGR Abfallentsorgungs-Gesellschaft Ruhrgebiet mbH, we have analyzed the current compaction system at the Datteln central landfill site and developed optimization options," says Ralf Thiele, geotechnics professor at HTWK Leipzig.



The HTWK team carried out extensive investigations at two AGR landfill sites back in 2022. Their aim was to find out how great the potential for post-compaction is and how much additional landfill volume can be gained as a result. Both dynamic intensive compaction (DYNIV) and impulse compaction (IMPV) were used in the tests on smaller test fields. Although these compaction methods are frequently used in specialist civil engineering, their use in the context of waste disposal is new.



"We were surprised when we discovered that around ten percent compression was still possible in the effective depth range. This corresponds to a volume gain of around 0.5 cubic meters per square meter. This would make significantly longer running times possible on the huge landfill areas," says Thiele.



Background: Impulse compaction (IMPV)



In impulse compaction, a 9-tonne drop weight is dropped from a height of around 1.2 meters onto a compaction foot. The compaction foot is in constant contact with the soil so that the subsoil is compacted each time the drop weight hits the ground. The depth effect depends on the type of soil and the layer structure. Under favorable conditions, compaction depths of up to seven meters are possible.



Renewed trials with impulse compaction



In November 2023, the researchers carried out further tests with impulse compaction at the Datteln central landfill site - this time on much larger areas: Felix Oertel and Enrico Wendt from the Geotechnics department at HTWK Leipzig specialize in measurement campaigns like this. "We determined the settlement of the ground surface using photogrammetric measurements. To do this, we took images with a drone and generated digital surface models from them. This allowed us to compare the before and after states and determine the settlement volume from the difference," explains Oertel. They also used dynamic probing, a subsoil exploration method, to determine the effective depth and the depth-related compression.



The HTWK researchers have now evaluated the results: "The initial results already indicate that the successes achieved on the test fields will be exceeded in this large-scale application. The additional impulse compaction thus leads to maximum capacity utilization due to the denser storage of the already installed waste," says Wendt.



Procedure offers exemplary character



According to the HTWK team, this approach serves as a model for landfills throughout Germany. Together with AGR, they therefore published the results from 2022 at the 33rd Karlsruhe Landfill and Contaminated Sites Seminar in 2023, where they met with a great response. At the 20th Leipzig Landfill Conference on March 12 and 13, 2024 at the HTWK Leipzig, they presented the latest results to an expert audience.



"More efficient utilization of the landfill volume can improve the overall disposal situation. The collaboration between AGR Abfallentsorgungs-Gesellschaft Ruhrgebiet mbH and the Geotechnics department at HTWK Leipzig is thus making an important contribution to waste disposal security in Germany," says Detlef Löwe, AGR Head of Landfill Management.



Background: The Datteln central landfill site



Until 1999, AGR Abfallentsorgungs-Gesellschaft Ruhrgebiet mbH deposited class II municipal waste on an area of 20 hectares at the Datteln central landfill site. Inert waste such as soil and building rubble continued to be deposited until 2007. The landfill was closed in 2008. In view of the future lack of landfill capacity in the Ruhr metropolitan region, the Münster district government approved the continued use of the landfill for landfill operations from 2018. With the "landfill on landfill" solution, a good 300,000 tons of additional contaminated soil material could be deposited. Landfill operations at the Datteln central landfill site were finally discontinued at the end of 2023.



Geosciences at the HTWK Leipzig



Geosciences at HTWK Leipzig is an interdisciplinary team from the fields of civil engineering, mechanical engineering, geography and geology. It deals with topics relating to the macro- and micromechanics of soils and transfers its findings to practical construction processes and currently relevant cross-cutting topics such as digitalization and sustainability in geotechnics.



Geosciences is also a member of the Saxony⁵ transfer network of the five Saxon universities of applied sciences. In the "Sustainable construction" sub-project, research results are validated on a large scale at the GeoTechnikum - an experimental and demonstration space with outdoor test areas and a soil mechanics research laboratory - and demonstrated for partners from practice and science.



The article first appeared on the website of the Leipzig University of Applied Sciences.



published on 04.04.2024, by Dr. Franziska Böhl