The effect of shallow depth tunnelling on aboveground constructions
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ORIGINAL PAPER
The effect of shallow depth tunnelling on aboveground constructions Mete Kun
Received: 9 December 2013 / Accepted: 11 June 2014 # Saudi Society for Geosciences 2014
Abstract The investigation of the effect of resultant stress and stress distributions on the tunnel itself and the aboveground constructions due to underground mining activities (tunnelling, gallery excavation, etc.) in shallow depths (less than 50 m) and weak rock zones near residential areas is a significant and essential procedure. The poses of risk in aboveground constructions due to the tunnel construction in shallow depths and weak rock zones are emphasized in this study. The data calculated by empirical methods (subsidence, number of stability, angular distortion, etc.) are compared to the results of measurements and observations to be evaluated. Besides, the results of calculations and laboratory studies are evaluated on a numerical model by creating what-if scenarios and solutions. The necessity of careful observation of aboveground constructions, inspection of the projects simultaneously with empirical, analytical and numerical methods is revealed as the result of the study. Keywords Shallow tunnel . Aboveground constructions . Weak rock
Introduction The undisturbed state of stress (virgin) at shallow depth is much more sensitive to factors like weathering, irregular topography, residual stresses, erosion and melting of land ice than at greater depth. At shallow depth, irregular topography may alter both the stress directions and the stress magnitude, weathering may reduce the already low stresses, geological structures may create large destressed blocks and zones and residual stresses can create large anomalies in the state of stress (Töyrä 2006). M. Kun (*) Department of Mining Engineering, Dokuz Eylül University, Buca 35160, İzmir, Turkey e-mail: [email protected]
The role of virgin stress zone on the stability of underground openings is a well-determined fact. The overstress around an underground opening due to a secondary stress or failure zone depends on primary stress zone, geometry of the opening and the mechanical specifications of the wall rock. The determination of the most suitable choice for the primary stress zone is a reliving situation for both designers and operators if there are no restrictions for design parameters including the shape and location of the opening (Kun and Onargan 2013). Depending on many measurements of virgin stresses in different locations all around the world, variation of the main components of the virgin stress such as horizontal-vertical alignment, taking different values and differentiating in magnitude is a common situation (Amadei and Stephansson 1997). The virgin stress zone may be the highest, medium or lowest primal stress if it is depending on directions (such as anisotropic). According to Hoek and Brown (1980a), the determination of the geometry of an underground opening (axis ratio) should be done by selecting the most suitable one for the existing virgin stress zone in en
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