Protection of hydraulic resources in the plain of Alsace by confinment of an industrial spoil heap.
The Ochsenfeld site is located in the southern part of the Plain of Alsace at the base of the Vosges. It extends over three rural districts between Thann and Cernay and represents a surface of 83 ha. Presently it belongs to Millenium Chemicals, which is a producer of Titanium dioxide.
In the spoil heap built in 1930 they have been stocking, in addition to the dioxide fabrication waste, various chemical products have been stockpiled and have generated a significant acid pollution of the ground water in the plain of Alsace. In order to upgrade this site to the requirered environmental legislation level, the Owner has requested a bid for the design and construction for which Sita / Soletanche Bachy joint venture was awarded.
The chosen solution has been subject to long simulation studies and different situations have been considered particularly whether the site should be covered or not.
The solution chosen includes a peripheral wall, a drainage system outside of the confinment wall to prevent the flow of the external ground water, and an pumping system inside the confinment the objective of which is to keep the internal water table always below the exterior one in order to maintain a gradient generating a positive flow.
The confinment wall
The geology of the site includes recent coarse alluvial deposits composed of sands and pebbles, sometimes cemented, overlying a substratum of hardened conglomerates and reddish argillaceous Oligocene silts.
Owing to the soil strength encountered and programme restraints Soletanche Bachy selected 3 rigs with KS2 clamshells working in 3 shifts. The anti-acid slurry was produced by a mud plant with a capacity of 50 m3/h. This slurry should be able to resist long term chemical attack on the site due to the presence of sulphates (up to 4 g/l) and with a pH near 3 in some places. The addition of fly ash and specific additives to the slurry was able to provide such protection.
Due to the innovation and the means engaged on this project, total completion was achieved in five month.
Groundwater is one of the most complex issues to be resolved in geotechnics. During the start phase of a project, the proper techniques have to be chosen for building any cut-off walls that might be required, pumping (wells, filter points, etc.) and monitoring (piezometers) resources.
Soletanche Bachy, and its subsidiary Solenvironment, provide solutions for pollution issues, involving, for example: inertisation of waste, rehabilitation and treatment of polluted sites, cleaning of discharge to required environmental control levels, construction of waste storage facilities, protection of groundwater.
Through his subsidiary Sol Environment, Soletanche Bachy provides solutions to various pollution problems: stabilisation of waste, rehabilitation and treatment of polluted sites, cleaning of discharge to required environmental control levels, construction of waste storage facilities, protection of the water table.
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