Validation of Empirical Correlation for Squeezing Ground Conditions

A tunnel constructed within high in-situ stresses experiences either of the two phenomenon – Rock Burst or Squeezing Condition. Major concern while tunnel construction is to assess ground condition for the same. A tunnel experiences rock burst when the rock quality is very good without joints and overburden is greater than 800m, which is not very commonly encountered. While squeezing condition occurs in a rock mass having poor quality, which is generally experienced while tunnel construction. In this paper author have developed empirical correlation for assessing ground conditions (squeezing), tunnel deformation and support pressure with tunnel geometry, rock mass quality, in-situ stresses and support stiffness as input data. A data base comprising of about 14 tunnelling projects in squeezing was used in developing these correlations. In this paper a recently finished project has been considered in which tunnel deformations have been monitored and documented and the data has been used to validate the earlier developed correlations for assessing the ground conditions and tunnel deformations. In addition, numerical modelling has also been done using Phase² software (Rocscience Inc., Toranto, Canada) for the prediction of ground condition and tunnel deformation.