A model interface between Si and disordered SiO2 is obtained which incorporates the interface bonding pattern previously generated by first-principles molecular dynamics. The model is then characterized by comparing its properties with experimental data which provide an atomic-scale characterization of the interfacial region. The model is found to adequately reproduce the disordered nature of the oxide, the good coordination at the interface, the transition to stoichiometric SiO2, and the photoemission data. In particular, calculated Si 2p core-level shifts show a linear dependence on the number of nearest neighbor O atoms, confirming previous results obtained for interface models with ordered oxides. The comparisons with X-ray reflectivity and ion scattering experiments, which set constraints on the density in the oxide and on the size of the displacements in the upper part of the substrate, respectively, are also discussed.