SUMMARY

An unusual road has been designed and constructed in rugged topographic conditions of a deep canyon with vertical or subvertical sides. The road requires rock cuts up to 300 feet high which were excavated in competent sedimentary rocks which have three distinct sets of dividing planes: horizontal bedding and two sets of vertical joints, perpendicular to each other. The rock cuts were designed so that:

1) The cuts are stable;

2) Problem of rockfall is eliminated or reduced to a minimum;

3) Blasting produces a fairly clean face.

The finite element method, both without and with "joint elements", was applied with the aim to define the zones of tensile stresses in cliffs, both in the natural state, and after the cut excavation has been completed.

RESUME

Une route insolite a été projetée et^construite dansjes conditions topographiques ardues d'un canyon profond aux parois verticales fort excarpées. La route nécessite des talus dans la roche d'une élévation atteignant 300 pieds (91 m). Ces talus furent effectués dans la roche sédimentaire présentant trois caractéristiques distinctes de division: la stratification horizontale et deux séries de fissures verticales, perpendiculaires l'une à l'autre. Les talus de la roche furent établis de sorte que:

1) Les talus sont stables;

2) Le problème de chute de pierres est éliminé ou réduit;

3) L'explosion produit une surface relativement unie.

La méthode des éléments finis avec ou sans les "éléments de fissure" a été utilisée dans le but d'établir les zones de tension dans les falaises naturelles et après l'excavation des talus.

ZUSAMMENFASSUNG

Eine ausserordentliche Strasse wurde geplant und unter unebenen topografischen Verhältnissen in einer tiefen Schlucht mit senkrechten oder beinahe senkrechten Seiten gebaut. Es war notwendig die Felsbö- schungen bis zu 300 FUSS (91 Meter) tief auszuheben. Sie wurden ausgehoben in festem sedimentären Gestein, welches drei unterschiedliche Gruppen von Trennungsflächen hat: Horizontale Schichtung und zwei Systeme von Kluften die rechtwinkelig zueinander stehen. Die Felsböschungen wurden geplant so dass:

1) Die Böschungen stabil sind;

2) Das Steinschlagproblem beseitigt oder zu einem Minimum reduziert ist;

3) Sprengungen eine ziemlich saubere BöschungsoberflSche produzieren.

Die Finite-Elemente-Methode, ohne und ebenfalls mit Schichtfugen wurde benützt mit der Absicht die Zonen der Zugspannungen in natürlichen Felsen und nach dem Bbschungsaushub zu bestimmen.

INTRODUCTION

During 1973-1974, Atlantic Richfield Company, Operator of the Colony Development Operation, initiated the design and first stage construction of the United States' first commercial size shale oil plant near Grand Valley, Colorado. Although con- struction of the project was indefinitely deferred late in 1974 due to uncertainties, regarding national energy policy and the state of the economy, the work completed to date has required the application of modern design criteria to very unusual conditions. The shale oil complex was to be constructed on the Roan Plateau (elevation 8100 feet - 2469 m) on the drainage of Parachute Creek, a tributary to the Colorado River. A plant at this location required construction of a high quality access road beginning in the Parachute Creek Valley at about elevation 6450 feet (1966 m), and was complicated by right of way restrictions and the rugged topography in the canyon. The deep canyon is characterized by extensive talus slopes standing at or near their natural angle of repose, about 38°, with vertical or subvertical walls of considerable height above. A typical cross section of the canyon is shown in Figure 1. deals with the design of that portion of the road located within the vertical to subvertical cliff sections.

GEOTECHNICAL CONDITIONS

The Roan Plateau region is a conspicuous high- land located in the central portions of a large intermontane basin and is typical of an arid, maturely dissected plateau. It is cut by both intermittent and perennial streams of dendritic patterns which have cut narrow, steep-sided valleys or deep canyons with precipitous walls in the sedi- mentary rocks. Hanging valleys and box canyons are characteristic of the area. The stratigraphy of the region is dominated by the Green River Formation, a lacustrine deposit of the Eocene (Tertiary) Age which occupies the large structural basin of Piceance Creek. The rocks are essentially horizontally layered. As can be seen on Figure 1, two members of the Green River Formation outcrop in the canyon - the upper The road crosses these formations at a nearly continuous grade of 8 percent. Embankments were not economically feasible in most areas, particularly in the cliff sections, and the road was designed as a cut section with a total excavated width of about 60 feet. In the cliff formations this resulted in rock cuts of several hundred feet deep. This paper usually thin-layered, deeply weathered and tend to weather into rolling hills with slope angles of 25 to 38 degrees. Parachute Creek rocks consist primarily of competent and hard marl stones and shales, with no appreciable weathering.

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