This paper deals with the development and the verification of a soil model for tunneling under compressed air. The model is based on mixture theory treating the soil as a three-phase medium with the constituents: deformable soil skeleton, water and air. In the current coupled approach, the interactions between the individual phases are taken into account in a physically consistent manner, i.e. the flow of water and compressed air and the deformations of the soil skeleton are treated simultaneously. The incorporation of the model into a finite element code is verified using results from the literature as well as from laboratory tests particularly performed to this end.
For tunneling below the groundwater table deformations of the ground and surface settlements are caused by dewatering the soil and by the advance of the tunnel face. Application of compressed air as a means for dewatering of the soil in the vicinity of the tunnel face is motivated by the objective to get smaller ground settlements than by lowering the groundwater table by means of pumping wells and driving the tunnel under atmospheric conditions. In the first one, an uncoupled numerical approach, the flow of water and compressed air and the deformations of the soil are treated in two consecutive steps. Consequently, interactions between the fluid flow in the soil and the deformations of the soil are neglected. The second one, a coupled solution procedure, permits consideration of the intrinsic coupling of the process of dewatering with the Figure 1: Tunneling under compressed air deformations of the soil. Only the latter approach, which will be applied in this paper, allows to properly take into account the interactions of the flow of water and compressed air in the soil with the deformations of the soil skeleton in a physically consistent manner.
