Seismic protection of buildings using the innovative concept of Geotechnical Seismic Isolation (GSI) has emerged as a sustainable and economical alternative to the conventional base isolation system. The GSI system comprises horizontal layers of high damping, adequate stiffness, energy-absorbing material sandwiched between the natural soil and foundation. The present study aims to numerically investigate the performance of a 5-storeyed framed structure placed on a well-designed GSI system comprising sand-rubber mixtures, using finite element code Plaxis 3D. The structural elements of the superstructure were modelled as linear elastic using beam and plate elements. The maximum mesh size was made less than one-tenth of the wavelength of the frequency content of the input wave according to Kuhlemeyer and Lysmer criteria. Lateral boundaries were assigned viscous boundary conditions to simulate the behaviour of the infinite soil medium. The bottom surface is given a compliant base condition which could be able to simulate seismic excitations. The hardening soil model with the small-strain stiffness model is used to simulate SRM. This model can incorporate hysteretic material damping when subjected to dynamic loadings. The seismic response of the framed structure is considered for two cases of base conditions: (1) pure sand; (2) GSI layer; subjected to sinusoidal input motions. The acceleration and displacement response of the structure at each floor are computed. It is found that the acceleration and the lateral displacement of the structure resting on the GSI layer is substantially less than the structure resting on natural soil.