In this study, numerical analyses on interaction between a high density polyethylene (HDPE) pipeline and a loose and dense sand reinforced with a geogrid layer was performed in PLAXIS 2D, a software program run by finite element method (FEM). The diameter and thickness of the pipeline were chosen as 400 mm and 12 mm respectively. The pipeline was constructed in a trench with fill material in sandy soil. The center of the pipeline was located 1.40 m below the ground surface. The pipeline was analyzed under the effect of Kobe earthquake, which could be assumed as a real damaging seismic hazard. Vertical and horizontal displacement and strain values of the pipeline were compared for two different cases. For the first case, the pipeline was placed in sand without any geogrid reinforcement; for the second case, a geogrid layer was placed 20 cm above the pipeline crown. According to the results of the numerical analyses, the displacements obtained on the pipeline were lowered by placing geogrid above the pipeline. However, significant displacements which could give destructive damage to the pipeline were obtained in both dense and loose sand. Although geogrid reinforcement lowered the displacements, the pipeline could still be damaged. Maximum vertical displacement was measured higher than maximum horizontal displacement in loose sand whereas maximum horizontal displacement was higher than maximum vertical displacement in dense sand. Furthermore, vertical strain caused compression on the pipeline with geogrid reinforcement but extension without geogrid reinforcement.