Using intact rock brittleness for assessing TBM penetration

The paper reviews the history of the punch penetration test (PPT) as a laboratory method that is conducted on intact sample to measure the rock brittleness (BI). Further, the interaction of rock brittleness and penetration rate of tunnel boring machine (TBM) has been examined and some relationship was developed between the BI and TBM penetration. For this aim, four tunnel projects having various rock types were studied and then four different dataset is examined and discussed herein. It is stated that the test via BI can be perfectly utilized for assessing the boreability of rocks. In conclusion, it is found that there is a relationship between the BI and TBMs penetration with correlation coefficient (r) ranging from 0.34-0.81 for hard rocks condition; however this correlation is quite low (0.34) for weathered and very weak sedimentary rocks categorized as extremely low brittle. The obtained results can be accepted for hard rocks but it should be used with care for weathered weak rocks that does not show brittleness behavior under the indentor.