DETERMINATION OF OPTIMUM BOLTLENGTH IN UNDERGROUND OPENING

Abstract

This work deals with preliminary design of underground openings by means of Block Theory. The design method is based on identifying all the blocks of rock medium that can be formed at the excavation boundary The analytical methods through theories of elasticity and elasto plasticity do not offer directly the required support pressure for the design of underground openings. These theories require input parameters of mechanical characteristics, which do not match with field values. The geological information of joint sets is not at all input for the analysis. On the other hand the Block Theory through this geological input provides a suitable solution so as to offer support pressure. Support design is made on the basis of tatistical analysis of block height values for wedges forming with three joints, four joints, and five joints. The results of Block theory have been compared with Barton's theory and Elasto-plastic theory for bolt length and support pressure. Support pressure value has also been compared with the immediate and ultimate support pressure values of Barton's empirical approach. Determination of correlation factor for the results obtained from block theory for the values of bolt length and support pressure have been made corresponding to the Czech criterion and Elasto-plastic theory.