Abstract
In tunnelling, rock mass support is designed based on the observed rock mass conditions. These conditions are determined by rock mass characterization. Measurement while drilling (MWD), one such characterization method, acquires drill parameter data during drilling. These data can be used to predict rock mass conditions ahead of the face. In this study, grout-hole MWD data are collected at one of the main tunnels in the large infrastructural project Stockholm bypass tunnels. The normalized and filtered MWD data are correlated to the rock mass characteristics using multilinear regression and the Levenberg-Marquardt method. Although a strong numerical correlation cannot be obtained, the results are promising. As a result, a holistic visual approach, which linked the MWD parameters with the rock mass classification and rock support requirements, was developed.
Highlights
In Scandinavian hard rock tunnelling, the preferred excavation method is conventional drill and blast excavation
The scaled penetration rate residuals of the blocks in the tunnel are displayed in Fig. 3; these residuals were calculated with Eq 1 and are dimensionless
The findings show the difficulty of numerically correlating Measurement while drilling (MWD) values with rock mass properties and rock support requirements
Summary
In Scandinavian hard rock tunnelling, the preferred excavation method is conventional drill and blast excavation. This method has the flexibility required to excavate varying tunnel cross-sections under changing rock mass conditions. The rock mass support is based on predefined rock support classes updated by observations during the tunnel excavation. These observations follow standardized rock mass characterization systems, such as Bieniawski's (1973) rock mass rating (RMR), Barton et al.’s (1974) quality system (Q-system) or Hoek and Brown’s (1997) geological strength index (GSI). The predicted rock mass quality is verified, and when required, the rock support is altered, according to the
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