GEO2 Engineering B.V. regularly provides advice on dewatering. This also relates to the project Langestraat in Uithoorn, where there is the wish to enhance the current sewage system with an overflow tank connected to the existing water drainage canal.
The Langestraat in Uithoorn has been constructed on top of a former canal where, in about 1900, a shipyard was active. In this shipyard at that time ships were treated with (among other things) brown tar and coal tar, which has resulted in locally polluted ground.
Using the results of environmental science research, the extent of pollution has been surveyed, leading to the preparation of advice on dewatering, according to which the pollution will not spread out as a result of construction activities. The houses built (possibly) on shallow foundations have been borne in mind.
Using the finite element programme MicroFEM, a non-steady-state calculation of dewatering has been made in which (relating to a period of several days) insights can be gained into such aspects as the necessary rates of extraction, the lowering of the level of ground water, and any displacement of the pollution.
Using a temporary construction of sheet pile walls, the flow of water out of the adjacent canal and the displacement of the pollution can be limited.
Should dewatering be necessary in relation to the connected sewage system, a screen/boundary will be created between the dewatering and the pollution, using return sources. This ensures that there will be no flow of ground water from the pollution in the direction of the dewatering.
The following aspects are worked out as a part of this project:
- Inspection/examination of breakthrough during excavation;
- Testing of the construction of the temporary sheet pile wall;
- Influence of ground settlement on adjacent buildings resulting from temporary dewatering.