Determining parameters, including geomechanical characteristics of rocks or rock mass, initial stress state, underground water conditions, permeability, etc., with high accuracy is difficult and expensive due to the complexity of the geological conditions. On the other hand, analyzing the stability of tunnels and determining the behavioral characteristics of the rock mass with numerical methods has limitations in terms of the validity of the input and output data. One of the practical methods to solve these problems is the use of monitoring system in underground space, which aims to measure displacements and can give an estimate of the stability of structures and rock mass. One possible way to validate or determine parameters on site is the use of precision instruments and perform back analysis on the resulting deformation data. In this research, different back analysis methods are investigated to validate rock masses parameters in tunnels.
In the last decade, various numerical methods such as finite element method (FEM), boundary element method (BEM) and discrete element method (DEM) have been widely used in the field of rock mechanics to design structures such as e.g. tunnels, large underground spaces, dam foundations, etc. The mechanical behavior of such structures is extremely difficult to predict with sufficient accuracy due to a lack of knowledge of the rock mass properties. In other words, the validity of the predictions depends on the accuracy of the input data and chosen constitutive model and how closely they reflect actual rock mass behavior. Therefore, despite the use of accurate geological surveys and complex computer analysis, it is not surprising that the actual behavior of the structures differs from the predicted behavior.
To assess this problem, field measurements are performed on a regular basis during and after construction, which, in addition to get an idea of the stability of the structure, serves to re-evaluate geological prognoses and geomechanical input parameters. Usually it is aimed at minimizing the difference between the measured and the calculated deformation of the structure.
