In engineering practice, pipeline trenching has been adopted as one of effective protection options. Most previous studies mainly focused on the prediction of the seabed response around a single pipeline, although two tandem pipelines have been used in engineering practice for transporting hydrocarbons. This study aimed to investigate the wave–current induced liquefaction around two tandem pipes in a trench. A series of simulations were performed to explore the effect of the horizontal gap ratio of dual pipes in a shared trench on the seabed response, and the results were compared with a single trenched pipe. In the numerical model, we used an integrated two-dimensional model that was developed based on the Finite Volume Method (FVM) in OpenFOAM®. In terms of the flow field, VARANS (Volume-Averaged Reynolds Averaged Navier–Stokes) was applied to simulate the fluid motion, while Biot's consolidation equation was used to govern the seabed model. The numerical examples indicate that twin pipelines semi-buried in close proximity within the same trench significantly impact the flow patterns and seabed response around them. Furthermore, the self-weight of dual pipes, ocean currents and trench configuration have a considerable influence on the evaluation of the liquefaction distribution around two tandem pipelines in a trench.