This paper shows an application of the SPH software DualSPHysics coupled with ProjectChrono to debris flow modelling. To achieve a rigorous modelling of such flows, a validation of the method is conducted for viscous flows and mixtures. Velocity profiles, free surface shape and velocity of viscous surges are validated against well documented experimental data. It is, to the best of our knowledge, one of the few validations of the SPH approach for very viscous flows near the creeping threshold (Re~1). Mixtures of viscous fluid and granular elements are studied against a semi-empirical formula. The method is then applied to 2D debris flow surges with field like features. Surges are composed of a viscous Newtonian fluid and poly-disperse boulders. The flow of surges of different concentrations is studied and Froude numbers of real field measurements are retrieved. Such complex models are shown to be relevant to the study of debris flow dynamics.