ABSTRACT
Prediction of rock mass behavior is one of the most difficult problems of rock engineering in spite of rapid strides made in the recent years in the field of geomechanics. The most promising way to overcome these difficulties seems to be by back analysis of the deformations observed in the tunnel during excavation. Field measurements are a very powerful tool not only for monitoring the stability of underground media, but also for designing structures. An Indian case history was selected for analysis to assess the rock mass behavior using the back analysis approach. The monitored deformations in the tunnel, which were of the order of 8.9% the tunnel diameter, were back analysed. The results of the analysis estimated shear strains upto 15.32% which is much greater than the estimated critical shear strain of 2.9%, indicating severe instability due to excavation. Also the comparison between calculated and measured displacements show good agreement.
