The design and construction of the chinipas slope pipeline crossing

SAIPEM has been awarded the engineering, procurement and construction of "El Encino - Topolobampo" Natural Gas Pipeline Project in Mexico. The 30" pipeline begins in El Encino, in the state of Chihuahua, and terminates in Topolobampo, in the state of Sinaloa. It runs in a West-South West direction perpendicularly crossing the "Sierra Madre Occidental", a mountain range characterized by uneven morphology with deep and narrow valleys and steep slopes. Near the village of Santa Matilde, before reaching the Chinipas River, the pipeline route has to overcome a 150 meters high steep slope on the left side of the valley of Chinipas. This slope features a sub vertical rocky cliff with a 55 meters drop in the upper section. A trenchless crossing of the slope was designed and executed to safely cross the steep slope by means of raise borer and tunnel. Since the area was nearly inaccessible, SAIPEM, for the first time in the design of a trenchless crossing of slopes, has performed the geomechanical study using a remote sensing process based on the Structure from Motion (SfM) technique for a three-dimensional reconstruction of the outcrop of the cliff. The activity has been carried out in collaboration with the Department of Earth, Life and Environmental Science of the University of Urbino. The results of the study led to the optimization of the trenchless geometry maintaining the raise bore into the competent rock avoiding frequent lithological variations critical during the drilling and identifying a suitable tunnel entrance location.