In this paper, a failure compensation scheme is designed for affine nonlinear systems prone to actuator stuck failures unknown in time, magnitude and pattern. The design scheme utilizes an adaptive second order sliding mode control developed in a backstepping framework exploiting the advantages of both the methodologies. An adaptive law is used to estimate the unknown upper bounds of uncertainties introduced due to the occurrence of actuator failures and guarantees a globally bounded estimation. The proposed failure compensation scheme ensures effective failure accommodation while providing excellent transient and steady state performances compared to the basic scheme based on backstepping, with chattering free control inputs. Stability and asymptotic tracking in presence of unknown actuator failures at unknown time instants is proved for the proposed control scheme using Lyapunov criterion. Simulation results illustrate the effectiveness of the proposed methodology.