An Analytical model for calculation of invert up-lift pressure of tunnels in poor quality grounds

There are many researches and contributions on stress analysis of tunnel’s roof and wall. But there is not enough research on invert stress analysis, especially in soft grounds. In this paper it has been tried to introduce an analytical model for prediction and calculation of invert up-lift pressure in soil and very poor quality rock mass. Figure 1 shows the problem under tunnel’s structures. When the pressure is high tunnel designer must be considered an invert structure for control of instability under tunnel lining. The pressure can be occurred by swelling process in some rocks and soils with high value clay content when there is a variation in moisture. But this research has been focused on invert up-lift pressure just by field stress and geomechanics conditions. Stress concentration and pore pressure have been considered in the equilibrium limit analysis and Mohr-Columb failure criterion has been applied as a linear well-known formulation for soils and very jointed rock masses behavior.