Geotechnical characterization using geophysical tests in areas of high geological complexity and landslides for horizontal directional drilling design

Abstract

In August 2021, landslides occurred on the slope of the Cortinas sector over an area of more than three kilometers, which affected electrical towers, a national vehicle highway, an oil pipeline and a gas pipeline. Currently, these infrastructures have limitations in their operation, generating significant economic losses and therefore, in the case of the gas pipeline, the construction of a HDD of two thousand meters in length at depths of up to one hundred meters is proposed, with the purpose of being able to bypass the zones unstable and restore transportation to normal conditions. The design and construction of said work constitutes a challenge, since the project area has very special geological conditions, since the hillside deposits are very susceptible to failure and there is apparently a stress tensor of an active fault that directly affects the stability of the area. The projected HDD crosses a ravine and a slope with steep topography with difficult access, as well as different layers of sedimentary rock with intercalations, which are folded and highly fractured and saturated with water. These special conditions generated difficulties and opposed the completion of several attempts by other HDDs, but taking into account that this alternative constitutes basically the only solution from a technical point of view, it was necessary to carry out some borehole and multiple seismic geophysical tests and geoelectrical that would allow defining a detailed stratigraphic profile to be able to analyze the constructive feasibility and, in such case, the most appropriate method, as well as the geomechanically characterization of the rocks, since according to the numerical modeling they indicate that the stability of the drilling may be affected due to plasticization at its limits, with detachments of rock fragments and jamming of the tools necessary for its construction.

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