DRAINING ADVICE FOR CONTAMINATED SOIL
Providing dewatering advice is a regular activity within GEO2 Engineering B.V.. This was also the case for the Langestraat project in Uithoorn, where the existing sewer system was to be expanded with an overflow tank connecting to the existing watercourse. The Langestraat in Uithoorn was built on a former waterway where a shipyard was present around the year 1900. In this shipyard, the ships were treated with, among other things, brown tar and coal tar, which resulted in a locally polluted soil.The extent of the contamination has been mapped out through environmental research, after which a drainage recommendation has been drawn up whereby the contamination will not spread as a result of the work. Taking into account the (possibly) steel-founded houses.
Using the finite element program MicroFEM, a non-stationary dewatering calculation has been made in which over time (over a period of a few days) it is possible to look at, among other things, the required extraction flow rates, the reduction in the groundwater level and the displacement of the contamination. A temporary sheet pile wall construction prevents the influx of water from the adjacent waterway and limits the movement of the contamination. As soon as drainage is carried out for the connecting sewerage, a screen will be created between the drainage and the contamination by means of return sources. This ensures that there will be no groundwater flow from the contamination towards the pumping station.
The following aspects have been developed as part of this project:
- Control cracking during excavation;
- Constructive test temporary sheet pile wall;
- Settlement influence on adjoining areas as a result of the temporary dewatering.
