Numerical analyses of tunnel collapse and slope stability assessment under different filling material loadings: a case s
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ORIGINAL PAPER
Numerical analyses of tunnel collapse and slope stability assessment under different filling material loadings: a case study Zeinab Aliabadian & Mansour Sharafisafa & Mohammad Nazemi & Alireza Rezazadeh Khamene
Received: 10 July 2013 / Accepted: 16 January 2014 # Saudi Society for Geosciences 2014
Abstract To transfer the excess water from Sabzkouh River in central Iran to cities beyond the river, a mechanized tunnel is being excavated. During construction and support installation in the first 100 m, tunnel roof collapse occurred and was followed by ground settlement, so that a cavity was developed in ground surface. The cavity had to be filled in a short time before rainy season, since the water flow through cavity could extend the collapse area in both tunnel roof and ground surface. In order to fill the cavity, some filling methods with different materials consist of in situ soil, lightweight concrete, and pumice aggregate lightweight concrete (PALWC) were suggested. To analyse the load distribution and minimize the costs, a three-dimensional analysis was carried out. Tunnel support system was simulated numerically to further evaluate loading state on support system under different material loadings. Mohr-Coulomb material model was used to allow material failure. The modelling procedure was based on actual construction procedure. Firstly, in situ model was modelled without any excavation and was run to establish pre-stresses and displacement, then slope was supported, the tunnel was excavated and support was installed and finally cavity was simulated. The numerical results show that filling the cavity with soil will result in over loading on the support system and leads to instability of the slope. Other two suggested filling materials have acceptable load on support system, but PALWC was selected as the best filling material having minimum loading and guarantees slope stability.
Z. Aliabadian : M. Sharafisafa (*) : M. Nazemi Department of Mining and Metallurgy Engineering, Amirkabir University of Technology, 424 Hafez Ave., Tehran, Iran e-mail: [email protected] A. R. Khamene Faculty of Mining Engineering, Azad Southern Branch University, Tehran, Iran
Keywords Tunnel roof collapse . Ground settlement . Filling materials . Support system . Numerical modelling
Introduction Tunnelling in difficult geological conditions represents a thrust to the development of innovative techniques, or to the improvement of existing ones, devised to allow for an efficient tunnel excavation whereby ensuring the stability. Many equipments and technical provisions have been first introduced to face difficult conditions met in particular tunnel projects and have been later adopted in other similar situations, often after specific improvements (Mair 2008; Singh and Goel 2006). A soft ground medium often leads to difficult conditions in tunnelling, due to its poor mechanical properties and great water bearing capacity. The stress release induced by the excavation causes weakening and possible localized failure
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