Topal_subbed.qxp 30/3/09 09:10 Page 100
Measures to Establish a Safe Route for New and Existing Gas Pipelines
Between Turkey and Greece
a report by
Subsea & Pipelines
Tamer Topal and Muge Akin
Department of Geological Engineering, Middle East Technical University, Ankara
The Southern Europe Gas Ring Project has been developed to transport taken in six boreholes. Third, sieve and hydrometer analyses,
natural gas through Turkey and Greece from sources located in the Atterberg limits and soil classifications were carried out on disturbed
Caspian Basin, the Russian Federation, the Middle East, southern samples, and unit weight, water content, sieve and hydrometer
Mediterranean countries and other international sources, under the analysis and soil classifications were performed on undisturbed
auspices of the Interstate Oil and Gas Transport to Europe (INOGATE) samples. Additionally, consolidated drained (CD) triaxial tests were
of the EU Commission. The section of the Turkey–Greece natural gas carried out on undisturbed samples taken from a level corresponding
pipeline within Turkish territory starts at the existing Karacabey pig to the landslide failure surface. Lastly, borehole and trial pit logs, the
station and ends in Ipsala/Kipi. The line includes a 17km-long offshore results of laboratory tests and back analyses were all utilised to
section in the Marmara Sea and is approximately 300km long, of which perform a stability analysis and to suggest remedial measures in order
209km is in Turkey (see Figure 1). to solve the landslide problem in the area.
The construction work on the pipeline began in July 2005 and was Site Geology and Landslides
completed on 18 November 2007. The Turkey–Greece–Italy natural Claystone is the main rock type exposed in the study area above which
gas pipeline is the extension of the Turkey–Greece natural gas there is a soft–firm clayey level sliding down. Many landslides have
pipeline. Accordingly, the line would extend from Greece to Italy occurred in the study area. The landslides have a curved surface at
beneath the Adriatic Sea. The new natural gas pipeline – with a the crown. The movement type is rotational at the upper part of the
diameter of 0.90m – will carry 750 million cubic metres of natural gas landslide body, and becomes translational where the failure surface
in the first stage, which will rise to 11 billion cubic metres in 2012. reaches the claystone level. The toe parts of the landslides are near a
stream, so stream undercutting seems to play an important role in
The new pipeline route is next to an existing small-diameter pipeline triggering the movements. The landslides formed near the stream
near Karacabey (Bursa) (see Figure 1). However, the existing enlarge backwards, creating retrogressive movements.
pipeline was broken by a landslide on 20 February 2006 in the Keslik
(Karacabey) area. The landslide was 96m long and 48m wide (see Previous reports showed only the active landslides with well-defined
Figure 2). Although the existing pipeline was temporarily repaired, it crowns and flanks in the close vicinity of the pipeline. However, many of
was also deformed due to the small movement of the landslide.
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With the dormant landslides were not recognised due to the fact that erosion
this in mind, either the pipeline route needed to be relocated or the had partly removed the features indicating signs of movement. In this
landslide needed to be stabilised, as the pipeline system had to become context, the landslide damaging the old pipeline was an old landslide (see
re-operational within a short period of time. This was urgent due to the Figure 3) that was reactivated due to the rapid melting of snow and the
fact that the other parts of the pipeline had already been completed. human/anthropogenic effect. Relocation of the pipeline is not considered
to be feasible due to the existence of many landslides in the region.
In this article, lessons learned from previous geological studies
and suggestions to prevent the reactivation of the Karacabey Investigation and Analysis of the Landslide
landslide to establish a safe route for new and existing gas pipelines The investigation of the landslide included the opening of eight trial pits,
will be discussed. eight boreholes, sampling during SPT tests and use of a Shelby tube,
constant head permeability tests, inclinometer measurements and
A new site investigation programme was started with a review of laboratory tests. This investigation revealed that the landslide has a
the existing site investigation reports along the pipeline. A new thickness ranging between 1.90 and 12.40m (see Figure 3). The shear
geological and geotechnical campaign was initiated, including strength values of the landslide material were obtained from the back
field geological mapping, trial pitting, drilling with field tests, analyses and CD tests. The laboratory test results indicated that the
inclinometer measurements, laboratory testing and a limit equilibrium landslide material is mainly clay with high plasticity (CH). However,
analysis. As an alternative, the gathered data were used to suggest gravelly clay, low-plasticity clay, sandy clay, clayey sand, silt with low
remedial measures in order to prevent the reactivation of the plasticity and silty gravel also exist at some levels.
landslide. First, in order to accomplish this task, field geological
mapping was performed. In the landslide area, eight trial pits and A long-term stability analysis of the landslide was carried out for non-
eight boreholes were opened. Second, standard penetration tests circular slide using the Janbu method. Considering the site
(SPTs) were performed at 1m intervals, and undisturbed samples were characteristics, a seismic acceleration coefficient of 0.2g and a pore
taken with Shelby tubes. Constant head permeability tests pressure ratio of 0.2 were used. The long-term factor of safety of the
corresponding to three to seven different levels of each borehole landslide was found to be 0.67, which means that remedial measures
were conducted in all boreholes. Inclinometer measurements were should be taken into account.
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© TOUCH BRIEFINGS 2009
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