The face heading stability of underground constructions remains quite difficult to assess, especially when groundwater is present. To investigate this, an experimental microtunnel was excavated at shallow depth in soft ground, below the water table. In agreement with field measurements of the piezometric level changes, a three-dimensional finite element analysis of groundwater flow shows that the head losses are concentrated in the close vicinity of the tunnel face. Both numerical equilibrium analysis and field measurements were used to show that the resulting seepage forces substantially increase the supporting pressure required to ensure face stability.
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Pellet et al. (1993) studied this question.