The infinitesimal deformation analysis of the rate-independent Sekiguchi-Ohta model is formulated to include a class of two-invariant stored energy function considering initial state of stress. Elastic shear modulus is assumed to depend on pre-consolidation pressure and increase exponentially with strain-hardening parameter after yielding by taking damage effect on energy conservation into account. The principle of maximum plastic dissipation is connected to the associated flow rule while hardening/softening law is described by the hardening potential function defined to suit the model. The implicit integrative scheme is return mapping algorithm based on the Closest Point Projection method. The nonlinear analyses for stress-strain-strength under UU and CU tests were carried out to test the performance. It was found that the method is proven to robust, stable and accurate even in very large strain increments.