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Real time estimation for soil-tool interaction is a key method for the development of an autonomous excavation strategy. This paper presents a method for identifying the unknown soil parameters in real-time using a novel hybrid soil model. The hybrid models consist of the Mohr-Coulomb soil model and the Chen and Liu Upper Bound soil model. A switching mode is utilized to select a more accurate soil model to compute the failure force depending on the position of the excavator bucket. The Newton Raphson method is proposed to identify the soil parameters by minimizing the error between the experimental forces and the forces computed by the hybrid soil model. The results demonstrate that the proposed estimation scheme is accurate when comparing to the measured soil parameters and the experimental data. In addition, the high speed estimation time shows that the proposed method has a real time estimation capability. A very high robustness is achieved when compared to the least square method. The proposed method is very promising and highly suitable for the soil-tool interaction identification of an autonomous excavator in an unpredictable, dynamical and potentially hazardous environment.