Seismic Performance of Piled Raft Foundation at Al-Madinah City Center- Case Study

Ahmed Taha, M. Hesham El Naggar, Shehata E. Abdel Raheem

In the proceedings of: GeoOttawa 2017: 70th Canadian Geotechnical Conference; 12th joint with IAH-CNC

Session: Field Cases III

ABSTRACT: Al-Madinah City is the second holiest city in the Muslim world. Millions of visitors densely populate the city center around the Grand AlHaram Mosque most of the year. The recent seismic activity experienced near Al-Madinah city in 2009 triggered researchers and engineers to examine and improve building safety and structural seismic resistance. Owing to the seismic activities of the region and the geological nature of Al-Madinah, which comprises volcanic basaltic rocks surrounding clay rich agriculture land, piled-raft foundation was the design choice for many buildings including the Grand Mosque first extension project. The supporting piles extend deep into the basaltic stratum up to 50 m in some locations.The behavior of the piled raft foundation under earthquake loading would influence the seismic performance of the supported structure. Based on observations during past seismic events, it was suggested that the lateral inertial force of the building is supported by frictional resistance beneath the raft as well as piles shaft resistance. Moreover, the raft could potentially experience excessive settlement. As a result, the ratio of the load carried by the raft to the total structural load could increase after the earthquake event. The case study presented in this paper investigates the seismic performance of the piled raft foundation of a selected building in the city center. The seismic response of the piled raft foundation is analyzed using three-dimensional finite element model employing the computer program Plaxis 3D. The foundation response during the earthquakes is investigated. The result has shown that the piled raft configuration has better lateral resistance to the seismic loading than the piled cap configuration. ABSTRAIT La ville d'Al-Madinah est la deuxième ville la plus sainte du monde musulman. Des millions de visiteurs densément peuplent le centre-ville autour de la Grande mosquée (AlHaram) la plupart de l'année. L'activité sismique récente menée près de la ville d'Al-Madinah en 2009 a déclenché des chercheurs et des ingénieurs pour examiner et améliorer la sécurité des bâtiments et la résistance sismique structurale. En raison des activités sismiques de la région et de la nature géologique d'Al-Madinah, qui comprend des roches basaltiques volcaniques entourant une terre agricole riche en argile, la base de poteaux-radeaux a été choisie pour de nombreux bâtiments, y compris le projet de première extension de la Grande Mosquée. Les pieux de soutien s'étendent profondément dans la strate basaltique, jusqu'à 50 m dans certains endroits. Le comportement de la base de radeau empilée sous le chargement du tremblement de terre influencerait la performance sismique de la structure supportée. Sur la base des observations effectuées lors des événements sismiques passés, il a été suggéré que la force d'inertie latérale du bâtiment est soutenue par une résistance à la friction sous le radeau ainsi que la résistance de l'arbre des pieux. En outre, le radeau pourrait potentiellement avoir un règlement excessif. En conséquence, le rapport de la charge portée par le radeau à la charge structurelle totale pourrait augmenter après l'événement sismique. L'étude de cas présentée dans cet article étudie la performance sismique de la base de radeaux empilés d'un bâtiment sélectionné dans le centre-ville. La réponse sismique de la base de radeau empilée est analysée à l'aide d'un modèle à éléments finis tridimensionnels utilisant le programme informatique Plaxis 3D. La réponse de la fondation lors des tremblements de terre de conception est étudiée. Le résultat a montré que la configuration de radeau empilée a une meilleure résistance latérale au chargement sismique que la configuration de capuchon empilée. 1.1 Introduction The performance of piled raft foundation under seismic loads is an important subject when evaluating stability of structures, especially in highly active seismic regions. In general, the seismic design of a structure supported by a piled raft is conducted assuming fixed base condition. However, soil flexibility may result in significant changes in the response of the soil-pile-raft-structure system. Several pile foundations experienced significant damage during the1995 Kobe earthquake and 2005 Sumatra earthquake, which highlighted the importance of evaluating the seismic performance of piled foundations. Angelides et al. (1981) investigated the performance of piles under horizontal loads using finite element method. Their resultsdemonstrated that the stiffness of soil-pile decreased with increasing number of dynamic load cycles. The soil strength and the soil-pile interface resistance may degrade due the cyclic nature of the seismic loading, which can significantly reduce the lateral resistance of the foundation system. Chaudhary (2007) investigated the effectiveness of pile foundation in

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