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 - AIR PERMEABILITY OF CRACKED CONCRETE PLATES
The object of this paper is the prediction of the air flow through a cracked concrete wall element. Experimental data from permeability tests on large cracked reinforced concrete plates is used. The variation of the flow with the crack opening is investigated. A new empirical expression is developed for the calculation of the friction coefficient for the flow of air through a concrete crack. It is based on the general formulation of a turbulent or laminar flow of a gas between two parallel surfaces. It is a function of the crack width and of the maximum aggregate size of the concrete aggregate. Background Several studies have been conducted in the past 30 years to investigate air and water flow through cracked concrete (E.g. [Buss 72] and [Mivellaz 96]). Much of this research work was conducted in North America and Japan on behalf of the nuclear industry. It is clear form the review of the literature that there are still disagreements on the topic of the calculation of the air flow rate through cracked concrete [Fellay and Badoux 2001]. This paper focuses on the use of new experimental data to develop an expression for the friction coefficient for air flow through a crack in a reinforced concrete plate. The research presented below was conducted in the context of a research program on the Swissmetro transportation system. Swissmetro is an innovative concept for a very high-speed underground passenger Maglev type transportation system. One of its features is that the tunnels are under permanent partial vacuum, thus requiring “air proof” tunnel liners. The first objective of the research project was the experimental investigation of the “air tightness” of reinforced concrete elements. Experimental program An experimental testing program in two phases was conducted to compare and quantify the air permeability of reinforced concrete elements which could be used for Swissmetro tunnel liners. The objective of the first phase was to assess the influence of the concrete mix design on the permeability to gas of uncracked concrete samples. The permeability of eighteen concrete mixes was tested for different humidity levels and under different pressure differentials.
Leakage of gas through concrete cracks
Abstract This paper aims at formulating the gas leakage rate through cracks in concrete walls. Leakage tests were carried out using eighteen specimens. Five specimens with a reinforcing bar and thirteen without were tested. The kind of fine aggregate and the size of the coarse aggregate were varied. Crushed gravel was used as the coarse aggregate. In order to examine the dispersion of the experimental results, four or five specimens with the same dimensions and of the same type of concrete were tested. The experimental results were formulated accurately by an isothermal compressible-flow equation for each identified crack. The two-dimensional Poiseuille-flow equation was also applied successfully for a small leakage rate. The dispersion of the test data from the same specimens, the influence of the aggregate and the effect of the reinforcing bar are discussed. It is concluded that the influence of the aggregate can be neglected and that the reinforcing bar reduces the leakage rate. Finally, the gas leakage rate through a concrete crack is presented.