2015. A fully monitored excavation test on scale was performed for the Oosterweeltunnel in Antwerp, Belgium in order to assess soil behavior and specific techniques to be used in a later stage.
Part of the research project was to investigate how the glauconite sand and the Boom clay would react during the installation of long sheet piles during deep excavations. The Profound BAT-pore pressure sensors were among the monitoring instruments of this trial pit.
In order to relieve the busy traffic arteries of Antwerp (Belgium), the closing of the ring around Antwerp was put to study by BAM (Beheersmaatschappij Antwerpen Mobiel). The design of this construction requires detailed insight in the behaviour of the overconsolidated Boom clay layer during and after dewatering and removal of the covering soil layers. For this purpose a fully monitored excavation test was performed in order to assess soil behaviour and specific techniques to be used in anticipated projects in the Antwerp area. This paper specifically presents and evaluates the results regarding swell and pore pressures recorded in the Boom clay. From the monitoring results it can be derived that the Boom clay shows a quick response to a fluctuation in water level in the overlaying aquifer. The Boom clay also shows a severe pore pressure reduction as a result from loss on effective stress during excavation. These two effects should be considered separately. The underpressure is caused by swell hindered by a very low permeability of the Boom clay. Up to 50% of the effective stress reduction can be transferred into a pore pressure reduction. This condition results in a long term dissipation and swell process towards a gradient of approximately 25 kPa pressure increase per m depth increase. This effect intersects with the original hydraustatic pressure in the Boom clay.
Courtesy of the researchers of Witteveen + Bos you can read more about the specifics of the test here. This paper was the source for an article in the Dutch magazine Geotechniek number 5/December 2015, the Dutch magazine for geotechnical engineering.