Why the future of rock mass classification systems requires revisiting their empirical past

Despite recent efforts, digitisation in rock engineering still suffers from the difficulty in standardising and statistically analysing databases that are created by a process of quantification of qualitative assessments. Indeed, neither digitisation nor digitalisation have to date been used to drive changes to the principles upon which, for example, the geotechnical data collection process is founded, some of which have not changed in several decades. There is an empirical knowledge gap which cannot be bridged by the use of technology alone. In this context, this paper presents the results of what the authors call a rediscovery of rock mass classification systems, and a critical review of their definitions and limitations in helping engineers to integrate these methods and digital acquisition systems. This discussion has significant implications for the use of technology as a tool to directly determine rock mass classification ratings and for the application of machine learning to address rock engineering problems.

Estimating TBM Specific Energy by Employing the Rock Mass Strain Energy, A Case Study: Karaj – Tehran Water Conveyance Tunnel located in Iran

Recently energy costs are increasing so it is critical to master the challenge of energy efficiency. Energy consumption for drilling in tunnel Boring Machines (TBMs) is mainly determined by the specific energy. Specific energy is the amount of energy needed to excavate a unit volume of rock mass and is considered one of the important parameters used for performance prediction of TBMs. This study tries to apply the strain energy of a rock mass to develop a new method for foretelling specific energy for TBM. The area under complete stress–strain curve is known as strain energy which is pertinent to the rock mass behavior, pre and post failure properties, peak strain and post peak strain. In this study statistical analysis performed through collected actual data from Karaj Tehran Water Conveyance Tunnel revealed a new relationship between the specific energy used by TBM (SE) and the strain energy. For more detailed study the rock mass classification is performed with respect to the geological strength index and all geological units are then classified in three classes and the specific energy of TBM is predicted based on the strain energy of rock mass for each three classes. The results reveals that two parameters of the specific energy and the strain energy are in a direct relation whose correlation is increased with considering the rock mass classification based on the post peak behavior of rock mass.