Abstract: A series of 1g physical model tests are carried out to investigate the tunnelling effects on existing pipelines. A tunnel is excavated directly underneath the existing pipeline. The tunneling-induced pipeline deformation mechanism and the stress field around the pipeline are studied. In addition, three-dimensional discrete element back-analyses (PFC^3D) are conducted to improve the understanding of soil-pipe interaction problem. Based on the measured and computed results, change of the tunneling-induced stress, displacement, shear strain and bending moment in the existing pipeline are analyzed. The findings in this study can give theoretical basis for the reinforcement design of pipelines.