Building on an old dump
The communities Giesen and Harsum along with the City of Hildesheim, Germany jointly planned the construction of a commerce park covering an area of 240ha.
The section of the premises on which buildings were to be erected encompassed an area of 50ha. The only access road passed over a former garbage and building-trash landfill. Dumping in this area was still taking place until the end of the 60s. Overburden was placed in the lower 1.5 - 4m, over this there was building trash in the southern area and household/commercial garbage in the northern area.
The entire landfill was covered over with about 1.30 m of silty, fine-sand dirt. Since no other access route was available, an economically feasible, technically sound solution had to be found for this route. Earth replacement in the entrance area was rejected alone due to the high cost of moving the material into another landfill and the emission problems associated with this type of solution.
Therefore vibration concrete columns with a load distribution layer was proposed to improve the load-bearing capacity of the subsoil. A total of 920 mortared vibration concrete columns made of 2/32mm crushed grain with blast furnace slag cement were produced. The columns extend 0.5 - 1.0m into the primary ground. The geogrid reinforced load-distribution layer consists of two 30cm thick layers of incinerated household garbage slag and two layers of Secugrid 400/40 R6 geogrid. This geogrid, made of monolithic polyester flat bars with welded nodes, was laid out once in the longitudinal direction and once in the traverse direction. The entire load-bearing structure then received a 29m wide additional seal with a synthetic sealing liner, both sides protected with geotextiles.
An 8m x 10m test bed with two horizontal inclinometer paths was built to test the functionality and, in particular the settling behaviour, of the chosen construction. This test bed was later integrated into the final project. Once both geogrid layers and the load-distribution layers were installed, the load-bearing capacity was tested at various points with loading plate pressure experiments. All measured Ev2 values were over the required minimum value of 45 MN/m². The inclinometer measurements in the test bed revealed settling from 0 mm over the columns to 2mm between columns. The permissible sag of 155mm, which would have fully extended the geogrid to its tolerance limit of 4 %, was therefore markedly undershot.
The chosen construction with Secugrid 400/40 R6 exceeded by far the prescribed requirements.
Year of construction: 2002
City / Country: Giesen-Harsum, Hildesheim, Germany
Secugrid 400/40 R6 11.000sqm
Commerce Park Giesen-Harsum-Hildesheim case study
Building on an old dump