De Wielingen Development nv
23 June 2017
A sensitive environment
For the excavation and construction of two underground levels for of a retirement home in De Panne, AGT created the dewatering concept and investigated the environmental impact of dewatering. The project was challenging because of the sensitive environmental conditions. The construction site was situated in a protected dune area characterised by highly permeable dune sand. Additionally the site was surrounded by a Natura 2000 protected area, dune pans, tidal activity and characterized by a freshwater-saltwater balance in the groundwater. Because of the special location of the construction site, the environmental impact of dewatering had to be investigated in detail.
Field measurements
During a drilling campaign, a strong clay-containing zone was discovered at a depth of 15 m with a thickness of ca. 5 m. The groundwater level above and underneath the clay layer was measured using piezometers. The measurements showed a 1,25 m difference in water levels above and underneath the clay layer indicating that the clay layer represents a hydraulic barrier.
In order to perform reinjection of the groundwater, the salt content of the groundwater has been measured. EM measurements were performed in boreholes and indicated the presence of fresh water. A groundwater model was created in order to simulate the different dewatering scenarios and to investigate their environmental impact.
The dewatering concept
In order to minimize the environmental impact of dewatering, water-retaining walls were implemented until (and crossing) the clay layer. This created a hydraulically sealed excavation pit which resulted in a negligible change in the groundwater level in the neighbouring protected areas. The drainage water was reinjected along the northern coastline and the southern Natura 2000 protected area. In this way, the groundwater level in the protected areas was almost not affected by the construction dewatering. Both the groundwater level and the quality of the drainage water were monitored during the works.
Protection of the environment
This study is a good example of cooperation between the consultancy company providing the dewatering concept and the construction team to execute a technically challenging project with maximum protection of the surrounding environment. The dewatering studies of AGT are always in line with the new dewatering guidelines.
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Dewatering needs to be carried out in in an area with restrictions (i.e. in a Natura 2000 area or in a polluted area…)?
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