Rock mass classification for rock mass in tunnelling and underground excavation - Development, limitation and way forward

In the last few decades, rock mass classification had been used intensively in engineering design. The concern arises for the potential occurrence of localized or global rock mass failure due to geological (such as discontinuities, water, weathering) and non-geological (such as construction load, vibration) factors should be taken into consideration. The ability of a classification system to represent the rock mass condition in a straightforward and effective way can assist in engineering works. Two classification systems can be applied in underground construction such as tunneling and mining. In tunnel construction, the Rock Mass Rating (RMR), Q System, Japanese Highway (JH) Method, Geological Strength Index (GSI) and Rock Mass Quality Rating (RMQR) are commonly used. However, these systems cannot be applied for rock mass covered by shotcrete due to difficulty in observing the discontinuity planes. Therefore, a new investigation method and rock mass classification for rock mass covered by shotcrete is vital to overcome this limitation.