ABSTRACT
The Ventilation Test (VE) has been performed in a 10 m section of a 1.3 m diameter unlined microtunnel excavated in the Mont Terri underground laboratory (Figure 1).
The Mont Terri laboratory (Thury & Bossart 1999) has been excavated in Opalinus clay, a stiff overconsolidated clay of Lower Aalenian age (Middle Jurassic) found in the Jura mountains of Northern Switzerland. There are three slightly different facies containing different mineral proportions: a shaly facies in the lower part of the deposit, a 15 m thick sandy-silty facies in the centre and a sandy facies interstratified with shaly facies in the upper part. The content of clay minerals may range from 40% to 80%, depending on the facies. The clay was sedimented in marine conditions, it is very strongly bedded and its total thickness is about 160 m. In the location of the Mont Terri laboratory, overburden varies between 250 and 320 m. The laboratory is situated in an asymmetrical anticline formed during the folding of the Jura Mountains. As a result, the rock strata dip with an angle of 25°–45o to the southeast. Information on the properties of Opalinus clay has been reported in Bock (2001), Wileveau (2005), Gens (2012).
