This paper analyses the electromagnetic (EM) wave scattering from an object buried between two random rough interfaces. We present a rigorous numerical EM model based on the boundary integral equation method that separates the different sensed media, which is discretized by the method of moments. The resulting linear system is resolved by a fast method called GPILE (Generalized Propagation Inside Layer Expansion), which makes it possible to reduce the complexity of the inversion of the impedance matrix and to isolate the different contributions to the overall scattering process. This method is then applied to a roadway sensed by GPR, with a view to calculating its time-domain response. The practical objective of this analysis is to study the impact of an embedded object inside a complex multilayered medium on the GPR signal.