Prediction of ground conditions for tunnelling

The knowledge of the ground condition plays an important role in selection of excavation method and designing a support system for underground openings. The ground condition is stable / elastic or falling / squeezing depending upon the insitu stress and the rock mass strength. Tunneling in elastic and the competent ground condition can face two situations—(1) where no supports are required— a self-supporting condition, and (2) where supports are required for stability; non-squeezing condition. The worldwide experience is that tunneling through the squeezing ground condition is a very slow and problematic process, because the rock mass around the opening loses its inherent strength under the influence of insitu stresses. Tunneling under the non-squeezing ground condition, on the other hand, is comparatively safe and easy because the inherent strength of the rock mass is maintained. Therefore, the important step is to assess whether a tunnel would experience a squeezing ground condition or a non-squeezing ground condition.