PREMETRO TUNNEL UNDER THE RIVER SCHELDT, ANTWERP - GEOTECHNICAL SITE INVESTIGATION AND INSTRUMENTATION . TUNNEL CONSTRUCTION 90. PAPERS PRESENTED AT THE TUNNEL CONSTRUCTION 90 CONFERENCE, ORGANIZED BY THE INSTITUTION OF MINING AND METALLURGY, LONDON, 3-4 APRIL, 1990

This paper presents details of (a) the geotechnical site investigation undertaken prior to the construction of the Premetro tunnel under the river Scheldt in Antwerp; and (b) the instrumentation programme during construction. The site investigation included: cone penetration tests, pressuremeter tests, borings and seismic surveys in the river and on both river banks. Geotechnical parameters were determined in laboratory tests on undisturbed samples taken in the borings. The tunnel was built using a hydroshield tunnel boring machine and a segmental concrete lining. On the right river bank the tunnel passes underneath a renovated existing quaywall and some historically valuable buildings. An extensive instrumentation programme was applied. Pressure cells were installed on the tunnel lining. On the right river bank extensometers and inclinometers were installed to measure the vertical and horizontal displacements of the quaywall, the soil movements around the tunnel and the settlements near the historic buildings. Based on the measurements of the total pressure cells an approximate correlation with the calculated values was noticed. The measurements on the extensometers and the inclinometers showed soil movements around the tunnel of maximum 5 mm. During the tunnelling works only small settlements at ground level were recorded. The chosen construction techniques resulted in differential settlements which are well below the criterion of 1/500 for the angular distortion at which damage to the classified houses could occur. For the covering abstract of the conference see IRRD 828810.