Highway cut made in a rock formation with precarious stability

S. Herrera, J.J. Schmitter, J. Colonia, V.H. Macedo, E.A. Reynoso

Dans les comptes rendus d’articles de la conférence: GEO2011: 64th Canadian Geotechnical Conference, 14th Pan-American Conference on Soil Mechanics and Geotechnical Engineering, 5th Pan-American Conference on Teaching and Learning of Geotechnical Engineering

Session: Mining and Rock Mechanics

ABSTRACT: The paper describes the peculiar deformational behavior observed in the vicinity of a 60 m tall highway cut, where the natural slope of the surrounding ground is of about 33% (18°). A description of the observed behavior and comments about its stabilization are included.

RÉSUMÉ: L´article décrit le particulier comportement deformationel observé dans le contour d´une coupe de route de plus de 60 m de haut, où l´inclinaison naturelle de la pente où fut excavé est de l´ordre de 33% (18°). On inclu la description du comportement observé et les commentaires en ce qui concerne son stabilisation. 1 BACKGROUND The transcendental mission of communication that since the beginning of the last century has been accomplished by the historic federal highway connecting the capital city of Mexico with the port of Tuxpan and the northern part of the state of Veracruz, crossing the states of México, Hidalgo, Puebla and Veracruz. This communication link is currently being upgraded through the construction of the new Mexico City-Tuxpan expressway road and once completed will be operated under the scheme of a concession granted in a bidding process by the Secretaría de Comunicaciones y Transportes, the highway branch of the federal government. Once in operation the improved highway will be reduced by 26 km to a total length of 300 km that presently have to be traveled to interconnect Mexico City with the port of Tuxpan, in the Gulf of Mexico. With the new toll road, whose concessionaire is the consortium known as AUNETI (Autovía Necaxa-Tihuatlán), transportation of passengers and freight will be expedited to alleviate the existing federal highway with only two traffic lanes accommodated in an extraordinarily winding topographic alignment with frequent encounters of rain and fog. After this new highway is completed, the traveling time between both extremes Mexico City and Tuxpan seaport, will be reduced from five hours to approximately two and a half. The execution of the final sections of this new toll road, namely Nuevo Necaxa-Ávila Camacho and Ávila Camacho-Tihuatlán, will be the responsibility of the contracting corporation CONNET (Constructora Nuevo Necaxa-Tihuatlán). In the first of these two stretches of the road, the so called Cut XV is located, in the vicinity of station km 845+250, whose behavior and stabilization constitute the main objective of the paper presented herein. 2 GEOLOGIC AND GEOTECHNICAL FRAMEWORKS 2.1 Regional geology The area where the highway project is being developed is located at the boundaries of the geologic provinces known as Eje Neovolcánico and Sierra Madre Oriental. Outcroppings are found of sedimentary rocks from Upper Jurassic, Lower and Upper Cretaceous and Tertiary (Paleocene) constituting what it is known as Anticlinorio de Villa Juárez. The sedimentary layers and the main structures of the folding present a general NW-SE orientation dipping toward the SW and forming in general terms recumbent structures of asymmetric type. The deposits from the Quaternary are associated to basaltic lave flows and to their pyroclastic components such as tuffs and breccias with the same composition. From the Recent age there exist talus and fluvial deposits appearing in low lying areas and occasionally covering important areas at hillsides whenever they have been produced by large landslides. The main feature of the area refers to the largest part of the area that evidences an advanced and deep degree of weathering due to the climatic conditions that have endured and that still prevail. At some cliff zones there are important outcrops where sedimentary and volcanic rocks have been exposed due to the intense erosion produced by the streams running across this region, particularly that of San Marcos River. Streams and gorges in the area develop a quite irregular drainage network that follows a direction sensibly parallel and perpendicular to the strike of the stratification planes. From a geotechnical point of view, it can be considered that the site being studied corresponds to the most difficult zone of the Mexican Republic to develop infrastructure works due to three main aspects: Type and lithological variety that is encountered in the area. Climate, including high rainfall rates.

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