OTSA is a free online program for determining a circular tunnel deformation, based on the simplified method using Mohr-Coulomb failure criterion as discussed in Hoek (1999). The Ground Reaction Curve (GRC) will be constructed from the elasto-plastic solution of a circular tunnel subject to a uniform far field stress and uniform internal pressure. Multiple support types (i.e. Steel set, shotcrete and rock bolt) have been provided. You may combine more than one support type in the same model.