Abstract
This paper presents a method for studying the variation in shear strength of soil due to the air flow in compressed-air tunneling. The method is based on application of the shear strength theories of unsaturated soils in conjunction with a finite element model, developed by the authors, for analyzing the flow of the air through soils. The formulation of the problem, the numerical model, the design and modification of the triaxial cell and the laboratory testing program, and the results are presented and studied with particular reference to compressed-air tunneling. The results are presented and interpreted using the concepts and theory of shear strength for unsaturated soils. The results of the tests indicate the way in which the air pressure increases the stability of the ground, besides being an internal support, prior to the installation of the temporary or permanent lining. From the results of the tests, a three-dimensional failure envelope was plotted that can be used to predict the change in shear strength of the soil due to a change in the air pressure, in compressed-air tunneling. This information can be used to assess the risk of tunnel collapse and blow out. It also improves the current understanding of the interaction between the compressed-air tunneling method and the ground.Key words: compressed-air tunneling, air flow, unsaturated soils, shear strength.
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