An elasto-plastic three phase model for partially saturated soil for the finite element simulation of compressed air support in tunnelling

• Published in: International journal for numerical and analytical methods in geomechanics 2010-04, Vol.34 (6), p.605-625
• Main Authors: Nagel, F., Meschke, G.
• Format: Article
• Language: English
• Subjects: Applied sciences; Buildings. Public works; Compressed air; Computation methods. Tables. Charts; Computational fluid dynamics; Computer simulation; Exact sciences and technology; finite element method; Fluid flow; Geotechnics; Mathematical analysis; Mathematical models; partially saturated soil; Partially saturated soils; shield tunnelling; Soil investigations. Testing; Structural analysis. Stresses; theory of porous media; Tunnelling; Tunnels, galleries
• ISSN: 0363-9061; 1096-9853; 1096-9853
• DOI: 10.1002/nag.828

This paper presents a fully coupled finite element formulation for partially saturated soil as a triphasic porous material, which has been developed for the simulation of shield tunnelling with heading face support using compressed air. While for many numerical simulations in geotechnics use of a two‐phase soil model is sufficient, the simulation of compressed air support demands the use of a three‐phase model with the consideration of air as a separate phase. A multiphase model for soft soils is developed, in which the individual constituents of the soil—the soil skeleton, the fluid and the gaseous phase—and their interactions are considered. The triphasic model is formulated within the framework of the theory of porous media, based upon balance equations and constitutive relations for the soil constituents and their mixture. An elasto‐plastic, cam–clay type model is extended to partially saturated soil conditions by incorporating capillary pressure according to the Barcelona basic model. The hydraulic properties of the soil are described via DARCY's law and the soil–water characteristic curve after VAN GENUCHTEN. Water is modelled as an incompressible and air as a compressible phase. The model is validated by means of selected benchmark problems. The applicability of the model to geotechnical problems is demonstrated by results from the simulation of a compressed air intervention in shield tunnelling. Copyright © 2009 John Wiley & Sons, Ltd.