A new natural gas pipeline is under construction to provide the gas interconnection between Turkey and Greece, as well as to create gas ring for southern Europe. The new pipeline 0.90 m in diameter will be constructed next to an existing small diameter pipeline. However, the existing pipeline was broken by a landslide occurred in February 2006 near Karacabey (Bursa). In order to investigate the causes of the landslide and suggest possible remedial measures, geological and geotechnical investigations including surface geological mapping, trial pitting, drilling with field tests, laboratory testing, and limit equilibrium analysis were carried out. Based on the gathered data, possible remedial measures are suggested to prevent the reactivation of the landslide.