EXPERIMENTAL RESEARCH FOR THE LINERS OF THE SWISSMETRO TUNNELS
Swissmetro is an innovative concept for a very high-speed underground passenger transportation system. One of its features is that the small diameter tunnels are under permanent partial vacuum. This paper presents the results of an experimental research program conducted on the behavior of concrete liners subjected to service conditions of Swissmetro tunnels. In one series of tests air flow was measured through cracked concrete subjected to a differential of air pressure. In a second series of tests, concrete elements were subjected to a large number of cycles of pressure variations under partial vacuum conditions to investigate possible degradation of the concrete surface properties.
Swissmetro - Tests on Air Permeability of Concrete
Air-tightness of the concrete lining is a critical factor for a railway tunnel to be operated under partial vacuum. The testing described in this article investigates the influence on air permeability of aggregate composition (sand content, maximum grain size), type of cement, addition of steel fibers, degree of saturation of the concrete, and use of a curing compound. Laboratory testing was performed on samples taken from 18 concrete wall elements representing a range of pumped concrete mixtures. Fresh-concrete properties, compressive strength, and porosity were also measured. This report handles the first 12 concrete mixtures. Evaluation of the remaining testing is still in progress.
Comparison of Binaural Release from Forward Masking in Animals and Humans. Electrophysiological Studies
Evoked potentials in the inferior colliculus and auditory areas of the cortex were studied in anesthetized guinea pigs and long-latency auditory evoked potentials (LAEP) were studied in waking humans using sequential binaural presentation of pairs of clicks – the masker and the masked signal – with a variable interval between them, to provide the conditions needed for the psychophysical phenomenon of direct forward masking. Introduction of phase differences between the masker and the masked signal led to decreases in suppression of responses to the masked signal and to faster recovery of the reaction types recorded. The greatest relative differences between response magnitudes to antiphase and synphase masked signals were seen at the beginning of the recovery process, and were 1.6, 1.5, and 1.4 respectively for responses from the inferior colliculus, auditory area of the cortex, and LAEP at stimulus intensities of 50–65 dB sound pressure level, differences subsequently decreasing to zero. There was a positive correlation between this measure and the stimulus intensity. The greatest differences between the time at which the recovery process ended for responses to antiphase and synphase masked signals were 4, 250, and about 2000 msec respectively for the inferior colliculus, auditory area of the cortex, and LAEP.