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An inventory for evaluating hazard and risk assessment of cut slopes in weak rocks along highways

  • Al-Homoud A. S. 
  • Tubeileh T. 
Article

Abstract

Several cases of instability of cut slopes along major highways in Jordan were reviewed in this study, in some detail. Emphasis was placed on the Amman-Irbid highway with the aim of establishing a wider data base of case studies and examining all possible mechanisms and factors influencing stability.

The study showed that major cut slope failures were caused by the presence of weak cohesive layers (mainly clayey marl) interbedded within other, mostly stronger, formations, in addition to the steep cutting angles and unfavourable dip of strata combined with relatively high piezometric surface brought about by poor surface and subsurface drainage.

The study also showed that sections II and III of Amman-Irbid highway suffer from an alarmingly high level of instability in cut slopes with more than 50 % of the entire route length was found to have high level of instability. No remedial measures were carried out so far to improve the overall situation of critical slopes. The amount of excavations required to render the cut slopes stable by satisfying acceptable standards of safety, was determined to be approximately 2.8 million cubic meters with an estimated cost of 10 million JD’s.

To investigate the influence of various parameters on slope stability, several analyses were performed in addition to back analyses to determine shear strength parameters. Data were obtained from previous in vestigations by local and international firms, screened and modified where needed, before being used in stability analyses. Considerable difference between back analysis and test result values for shear strength parameters were observed in many cases.

A classification system was developed for factors influencing landslides, bases on the case studies considered; a stability grading scheme was also introduced; the system was applied to several existing cases along Amman-Irbid highway, the resulting assessments were in agreement with the observed stability conditions.

Keywords

Rock Mass Safety Factor Slope Stability Back Analysis Shear Strength Parameter 

Glissements de terrain dans des déblais routiers réalisés dans des roches tendres en Jordanie

Résumé

L’article présente plusieurs cas d’instabilités de déblais le long de routes importantes de Jordanie. L’accent est mis sur la route Amman-Irbid, le but étant de mettre en place une base de données plus large et d’examiner tous les mécanismes et facteurs qui influencent l’instabilité.

L’étude a montré que la plupart des ruptures étaient dues à la présence de niveaux tendres (surtout des marnes argileuses) intercalés dans des formations en général plus résistantes, ainsi qu’aux pentes des talus, très raides, au pendage défavorable des couches, et à une surface piézométrique relativement élevée, le draînage de surface et de subsurface étant insuffisant.

L’étude a aussi mis en évidence que les sections II et III de la route Amman-Irbid souffrent d’un niveau beaucoup trop élevé d’instabilité des talus, plus de 50 % de la longueur étant instable. Aucune confortation n’a été entreprise jusqu’à présent. Le total des terrassements qu’il faudrait réaliser pour amener les talus à un état de stabilité satisfaisant les normes de sécurité a été estimé à environ 2,8 millions de mètres cubes.

Pour apprécier l’influence des différents paramètres sur la stabilité des pentes de talus, plusieurs analyses ont été faites pour définir les paramètres de résistance au cisaillement. Des données ont pu aussi être extraites d’études réalisées précédemment par des sociétés jordaniennes et étrangères. Dans de nombreux cas, on a constaté des différences considérables entre les données antérieures et les essais réalisés.

Un essai de classification des facteurs influençant les glissements, basé sur les exemples observés, a été proposé. Appliquées à plusieurs exemples le long de la route Amman-Irbid, les prévisions se sont avérés conformes aux observations faites.

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Copyright information

© International Assocaition of Engineering eology 1997

Authors and Affiliations

  • Al-Homoud A. S. 
    • 1
  • Tubeileh T. 
  1. 1.Civil Engineering Department Jordan University of Science and TechnologyIrbidJordan

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