MONITORING AND CONTROL SYSTEM IN AN AREA OF GEOTECHNICAL RISK UNSTABLE IN THE CAMISEA GAS TRANSPORT SYSTEM

摘要

The experience gained during the operation and maintenance activities on the Camisea Pipeline Gas Transport System (SDT) owned by TGP in Peru - which goes from the Amazon rainforest in the region of Cusco to the Pacific coast near Lima, along 729 Km - has led to the evolution and the optimization of the design, construction and maintenance processes regarding works focused on the stabilization of the slopes along the right of way of the pipeline carrying natural gas and natural gas liquid. This section of the right of way is 95 km long and crosses tropical mountains in the Amazon rainforest, in a transitional area between the Manugaly valley and the basin top boundary. It was noticed since 2005 that the right of way had being affected by a land slide consisting of a horizontal crack in the ground, between both pipelines and along them. So, after number of in-site inspections, the team concluded that the area was being affected by a large ground removal event. As a consequence, traces of geotechnical instability were found on the right side of the right of way, consisting of stress cracks, transverse settlements and leaks. All of those were affecting the stability conditions of the ground. From the annual in-site follow-up, monitoring and geotechnical testing, the team established that this process affecting the right of way was caused by a large mass removal process directly related to the increase of the imbalance rate of an old colluvial deposit below the entire area, triggered by the heavy rainfall in the area - ca. 3 500 mm a year, mainly between October and April. It is to be mentioned that the axis of the NG and NGL pipelines is located on the top of this colluvial deposit, which is susceptible to landslides. This is noticeable because of cracks present in the place. Local geomorphology and heavy deforestation - caused by locals- triggers an increase of the rainfall water filtration rate into the ground, thus speeding up the slide processes. Piezometers installed in the area showed high levels of the local water table. Movement readings are: top length: 70 m; length: 250 m; width: 150 m. Criteria for the construction of landslide mitigation structures in the pipeline area are being established based on a permanent land survey monitoring system - including inclinometers, piezometers and strain-gages - as this is a large regional movement. This control action allowed the operation to continue free of damages to the pipelines and under controlled costs.