Ever since its development, the GSI-Index has attracted interest in the field of rock engineering. In spite of some uncertainties and inadequacies, the GSI-Index has found acceptance for characterizing various types of rock masses. In this study, firstly a quantitative approach was presented to determine the GSI-Index for weak rock masses. Secondly, empirical equations were developed for the estimation of rock-load height and support pressure. Thirdly, the results obtained from the proposed empirical approach were compared with those acquired from closed-form and numerical solutions and a reasonable agreement was obtained. Finally, a new empirical approach that can be used in rock reinforcement design of tunnels excavated in poor and very poor rock masses was briefly presented. The developed design method was applied to the Malatya No: 7 railroad tunnel excavated in squeezing rock condition, miss-aligned due to stress and water effect, as well as having poor support conditions.
To estimate the support pressure in extremely weak rock mass accurately, it is essential that such rock mass be quantitatively characterized. In the characterization of poor and very poor rock masses, the application of existing GSI indices is hindered by the fact that the use of the index for weak rock mass is to some extent subjective and requires long-term experience [1, 2, 3, 4, 5, and 6]. The method presented in this paper deals with overcoming such inconveniences and uncertainties present in previous methods. In order to better characterize a weak rock mass, two important indicators, namely Broken Structural Domain (BSTR) and Joint Condition Index (Ijc) from Ünal?s M-RMR classification system [7] have been added to the procedure.
Reliable prediction of tunnel support pressure (rock load) is a difficult task in the area of tunnel engineering and has been highly subjective and open to argument. Starting with Terzaghi?s rock load concept [8], several empirical approaches using rock mass classification systems have been developed for the estimation of tunnel support pressure [9,10,11,12,13,14,15,16]. Among them, Barton?s Q-dependent and Ünal?s RMR-dependent approaches have been widely used.
The proposed empirical approach briefly presented in this paper is a sophisticated version of Ünal?s RMR-dependent approach, taking into consideration almost all important factors affecting the amount of rock load. The main advantage of this new approach lies in the fact that it is applicable to overstressed and squeezing rock mass.
