ORIGINAL ARTICLE Geotechnical assessment of a landslide along a natural gas pipeline for possible remediations (Karacabey-Turkey) Tamer Topal Æ Muge Akin Received: 7 November 2007 / Accepted: 4 April 2008 / Published online: 6 May 2008 Ó Springer-Verlag 2008 Abstract A new natural gas pipeline with a 0.90-m diameter is under construction to provide a gas connection between Turkey and Greece as well as to create a gas ring for southern Europe. The new pipeline route lies next to an existing small diameter gas pipeline broken by a landslide that occurred in February 2006 near Karacabey (Bursa). Although the existing pipeline has been temporarily repaired, either the pipeline route should be relocated or the landslide should be stabilized. The geological survey conducted in the study area reveals that relocation is not feasible due to the existence of other landslides in close vicinity to the site. In order to investigate the causes of the landslide and to suggest possible remedial measures, geo- technical investigations including surface geological mapping, trial pitting, drilling with field tests, inclinometer measurements, laboratory testing, and limit equilibrium analyses were conducted. The investigation revealed that the unconsolidated clayey soil slid on claystone along a non-circular failure surface. Based on the gathered data, possible remedial measures including partial removal of landslide material and construction of toe buttresses, slope flattening, lowering the pipeline, and surface drainage systems were evaluated. These are suggested to prevent the reactivation of the landslide, and thus to establish a safe route for both the existing and the new pipelines. Keywords Landslide Á Non-circular failure Á Remedial measure Á Pipeline Á Karacabey Á Turkey Introduction A new natural gas pipeline with a diameter of 0.90 m is under construction to provide a gas connection between Turkey and Greece, as well as to create a gas ring for southern Europe (Fig. 1). The pipeline system will carry 750 million m 3 natural gas in the first stage, and it is estimated that this will rise to 11 billion m 3 in 2012. The new pipeline route is next to an existing small diameter pipeline near Karacabey (Bursa). However, the existing pipeline was broken by a landslide that occurred on Feb- ruary 20, 2006 in the Keslik (Karacabey) area (Fig. 2). The landslide has a length of 96 m and a width of 48 m. Although the existing pipeline has been temporarily repaired, it has been deformed by the landslide. The new pipeline system is completed except in the problematic landslide zone, and the system should start to work within a very short period of time. Therefore, either the pipeline route should be relocated or the landslide should be sta- bilized, and this is urgent due to the fact that the other parts of the pipeline have already been completed and the system should start work immediately after solving the landslide problem. In this study, a geological survey is conducted in the close vicinity of the landslide for site appraisal related to other existing landslides and possible relocation of the pipeline route if feasible. In order to investigate the causes of the landslide and suggest possible remedial measures, geotechnical investigations including geological mapping, trial pitting, drilling with field tests, inclinometer mea- surements, laboratory testing, and a limit equilibrium analysis were conducted. On the basis of the data obtained, possible alternative remedial measures are suggested. In order to accomplish this task, firstly field geological mapping was performed. In the landslide area, eight trial T. Topal (&) Á M. Akin Department of Geological Engineering, Middle East Technical University (METU), 06531 Ankara, Turkey e-mail: topal@metu.edu.tr 123 Environ Geol (2009) 57:611–620 DOI 10.1007/s00254-008-1330-0