Optimization of Rock Bolt and Concrete Lining Combination in case of Awash-Kombolcha-Haragebeya Railway Tunnel Project

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Date

2017-07

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AAU

Abstract

Tunnels are crucial infrastructures used for passage of humans, cars, trains or utility lines. Among this, tunnels used for road or rail purpose needs a great attention. The tunnel to serve its intended function, rock bolt and concrete lining are provided based on the ground condition. These two support systems are worthy and need great consideration as their impact remain on tunnel cost and convergence. Thus the optimum uses of these support systems are a challenge which demands the best design solution. Consequently, the study on tunnel rock bolt and concrete lining combination optimization which need study and improving, worth researching a lot. In this paper which is a case study, based on the design of data for optimization, the most influential support elements are selected. For different parameter combinations, the finite element methods have been performed followed by forming displacement parameter correlation. Likewise, the cost is represented by using polynomial model. Considering displacement and cost functions, the optimum combination of rock bolt and concrete lining has been found. The result show that the optimum combination is found if the number of rock bolt is 15 and concrete lining thickness 25 cm with in the constraint bolts [7,23] and lining thickness [10cm,40cm]. The optimized combination is modeled using numerical model and analysis along with the verification. The finite element analysis result gives total displacement of 6.34cm. But the observed total displacement inside the tunnel is about 60mm which is less than the predicted displacement of optimum combination using numerical analysis. The induced shear on concrete lining is 96.85 KN/m which is lower than the shear capacity of concrete lining. The total cost of rock bolt & concrete lining accounted for the optimum combination is $30,700 per 34 m2 tunnel rock bolt and concrete lining construction. Parametric study performed on pre stress rock bolt shows that increasing number of rock bolt would slightly increase stress and strain. Conversely, the convergence of tunnel is reduced. Similarly the plastic points are greatly reduced because of the pre stress rock bolt.

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Keywords

Rock Bolt, Concrete Lining, Optimization, Combination, Equation

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