A COMPARISON OF 2D AND 3D NUMERICAL SIMULATION FOR TUNNEL EXCAVATION ACCOMPANIED BY MEASUREMENT RESULTS

Tunnel excavation leads to the redistribution of stress in rock mass. The primary support is not the structure that is to assume the load of the rock mass, but instead in interaction with the rock mass it represents part of the structural system. Deformation of the mass, caused by the progress of excavation, alters its primary stress state causing stress in the primary support. This compression, amongst other factors, depends on the stiffness of the mass and support work, including the shape and size of the tunnel cross section. The available computer methods in geotechnics, linear and non liner constitutional equations, as well as 2D and 3D models accompanied by the use of developed computer programs, are considerably more developed and sophisticated than what is posed by utilising a familiarity and description of geotechnical properties of materials that enter such a model. The calculation results are exceptionally dependent on the chosen model and the values of chosen geotechnical parameters. Intensive measuring during tunnel works in carbonate rock mass of a Croatian karst type have shown that the measured deformations are significantly greater than that obtained in calculations which utilise stiffness parameters gained from existing relationships with rock mass classifications and that the measured forms of deformation along the depth are significantly different than those calculated or anticipated in the design. Such measurements have allowed for the development of a new approach to determining the carbonate mass deformation modulus in Croatian karst. The paper presents a 2D and 3D numerical simulation for the Bobova Tunnel excavation on the D404 national roadway and their comparison with measurement results. In both simulations, a new approach is used to determine carbonate mass stiffness in Croatian karst which provides more reliable deformation forecasting of geotechnical structures.