Metaheuristic based backcalculation of rock mass parameters around tunnels

Thesis Type: Postgraduate

Institution Of The Thesis: Orta Doğu Teknik Üniversitesi, Faculty of Engineering, Department of Civil Engineering, Turkey

Approval Date: 2018


Supervisor: ONUR PEKCAN


Due to uncertainities in the ground conditions and the complexity of soil-structure interactions, the determination of accurate ground parameters, which are not only used in tunnel construction but in the design of all underground structures, have a great significance in having structures that are cost-efficient. Backcalculation methods which rely not only on laborotory and field tests but also on field monitoring and field data provide real structure conditions and therefore it is gaining popularity in geotechnical engineering. In this sense, when compared to the conventional methods, backcalculation methods are able to attain accurate geomechanical parameters of materials surrounding the tunnels with the help of deformation data that is observed in tunnel constuctions. Tunnels are especially significant as they compose a great part of all underground structures. Obtaining these parameters in a fast manner is important in terms of the calibration of the parameters that are gathered during the construction. In this study, a finite element based backcalculation is developed by using Simulated Annealing and Particle Swarm Optimization methods. On the developed platform, the metaheuristic based algorithms, which are embedded into the back analysis platform as an intelligent parameter selection method which provide data for the finite element method. The response of the tunnel structure is obtained via twodimensional finite element analyses. The developed back analysis platform is tested by using the deformation data which is gathered from the T26 tunnel construction within the scope of Ankara-Istanbul Highspeed railway project. The tunnel is opened with the New Austrian Tunnel Method and therefore, not only the rock mass parameters of the graphite-schist surrounding the tunnel but also the in-situ stress around the tunnel are backcalculated. Verifications is done by comparing the ground parameters that are gathered through the calculations with the laboratory results. It is observed that the success of the results is due to the optimization algorithm that has been used and the sensitivity of the measured values. The documented parameters can be used to better undertstand the rock mass behavior and to create more realistic models for the underground structures that have the same rock mass conditions. This study enabled to obtain the correct parameters in a fast and accurate manner by using optimization algorithms and finite element method for tunnels where backcalculation methods are used.