GPR has the proven ability to inspect invisible underground infrastructures such as utility tunnels and water pipelines. Simulation plays a critical role in interpreting GPR data while model reconstruction remains a big challenge, particularly for complicated scenarios. To ease the modelling complexity, this study proposed a workflow to improve the interoperability between the graphical design application, the geotechnical analyser, and the electromagnetic (EM) simulator. Taking water pipe leakage detection as an example, the geometric model was generated in Rhino and shared with FLAC3D for permeability simulation. Afterwards, coupling the graphical information using a Grasshopper plug-in with the saturation results via the Complex Refractive Index Model (CRIM), a detailed dielectric model got reconstructed in gprMax for FDTD simulations.