FAILURE MECHANISMS OF UNDERGROUND STRUCTURES DURING EARTHQUAKE: AN OVERVIEW

Ahmed Mahmoud, Mahmoud Hussien, Mourad Karray, Mohamed Chekired, C. Bessette, L. Jinga

Dans les comptes rendus d’articles de la conférence: GeoQuébec 2015: 68th Canadian Geotechnical Conference & 7th Canadian Permafrost Conference

Session: Earthquakes and Geohazards II / Séismes et géoaléas II

ABSTRACT: Geotechnical structures buried near the ground surface have a wide range of applications, from small-scale pipelines such as means of gas transmission, telecommunications, water supply, and sewerage pipelines, to large-scale structures including tunnels for various transportation systems. This paper provides an overview of the current understanding of the failure mechanisms of these structures due to earthquake loadings. Based on post-earthquake investigations, experimental laboratory data as well as numerical simulations of underground structures conducted in the current study by means of computer code, FLAC, it was found that movement of ground at seismic load may cause serious damage to those infrastructures. These serious damage is represented in two main types of failure has been occurred. First, stress-strain failure of the underground structure due to extra-stress and extra-deformation which as a result of soil movement at seismic. Second, state the stress failure of soil which lead to an uplift of underground structures and collapse of surround soil then disconnection of pipe joints between buried structure and tubes.

RÉSUMÉ: Les structures enfouies près de la surface du sol ont un large éventail d'applications, allant de tuyaux pour le transport de gaz, de télécommunications, d'approvisionnement en eau, et de canalisations d'assainissement domestique, à des structures à grande échelle, incluant les tunnels qui servent comme systèmes de transport. Cet article donne un aperçu sur les mécanismes de défaillance de ces types de structures lorsque soumises à des charges sismiques. Basé sur des observations post-séisme, des données de laboratoire ainsi que des simulations numériques d™une structure souterraine menées à l™aide du code informatique, FLAC, il a été constaté que le mouvement du sol sous chargement sismique peut causer d™importants dommages aux infrastructures souterraines. Ces dommages sont représentés sous deux types principaux de défaillance. Tout d'abord, l™augmentation excessif des contraintes dans la structure souterraine provoqué par les mouvements du sol durant le séisme et à l'interaction sol-structure. Deuxièmement, l™augmentation des pressions interstitielles et la perte de capacité du sol qui conduisent à un soulèvement de ces structures et à l'effondrement du sol qui les entoure suivie de la rupture ou la déconnexion des raccords de tuyaux entre la structure enterrée et les tubes. 1 0BINTRODUCTION Buried geotechnical structures are becoming more and more prevalent in the modern world because of the decreasing availability of ground space due to fast growing population (Yue and Li (2007). Underground infrastructure, serving for transport (e.g., highway tunnels and subway metro), utility (e.g., gas and water pipelines) and storage purposes (e.g., fuel storage and water tanks) has been a widespread alternative in redeveloping urban spaces to ease land congestion pressures. However, in the event of an earthquake, the functionality of these lifelines could be put in to risk especially in the liquefied soils (Chian, and Tokimatsu 2012). Many earthquakes (e.g. 2004 Niigata Chuetsu, 2007 Noto Hanto and 2007 Niigata Chuetsu-oki) caused serious damage to buried structures such as uplift of manholes and settlement of pavement above backfill soil for pipes (Yoshida et al. 2008). Haiti 2010 Earthquake resulted in severe destruction of essential systems (e.g. transportation and lifeline systems). One of losses is a lost 60% of the nation™s infrastructure (DesRoches et al. 2011). In fact, Public infrastructure in Canada appears highly vulnerable following decades of underinvestment, and may be severely challenged by a large earthquake. Because of the losses experienced, significant investments are required to retrofit these ageing systems to a better level of performance (Kovacs 2010). The majority of Canada™s public underground structures included no modern seismic engineering knowledge during the design and construction because almost 60 percent of Canada™s underground structures was put in place before 1960 (CSCE 2003). To study the mechanism of failure of underground structure, a series of tests to underground structures have been modeled. e.g., small-scale model tests was conducted with centrifugal test (Zhou et al. 2015; Kang 2010) and another models was solved by numerical analyses (Jung et al. 2013; Liu 2012; Xia et al. 2010; Liu and Song 2006; Liu and Song 2005). This model tests resulted an enormous failure to the ground (e.g. uplift of soil with the structure and settlement of surround soil) and/or the underground structures (e.g. deformation and extra stresses for the underground structure). In this paper, examples of underground structures damaging under earthquake loadings including uplift and/or collapse of the buried geotechnical structures will be presented first to be followed with method of physical and numerical modeling of infrastructures. Then, the failure mechanisms of underground structures due to earthquake loadings will be reviewed and discussed. Among failure mechanisms presented and detailed discussed in this paper, we can mention: 1) Shear failure of soil which occurs when the pore water pressure

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